Merge pull request #20585 from ClickHouse/persistent_nukeeper_log_storage

Persistent coordination log storage

contrib/NuRaft

@@ -1 +1 @@
-Subproject commit 7adf7ae33e7d5c307342431b577c8ab1025ee793
+Subproject commit 9a0d78de4b90546368d954b6434f0e9a823e8d80

docker/test/fasttest/run.sh

@@ -70,6 +70,7 @@ function start_server
         --path "$FASTTEST_DATA"
         --user_files_path "$FASTTEST_DATA/user_files"
         --top_level_domains_path "$FASTTEST_DATA/top_level_domains"
+        --test_keeper_server.log_storage_path "$FASTTEST_DATA/coordination"
     )
     clickhouse-server "${opts[@]}" &>> "$FASTTEST_OUTPUT/server.log" &
     server_pid=$!
@@ -375,7 +376,7 @@ function run_tests
         stop_server ||:
 
         # Clean the data so that there is no interference from the previous test run.
-        rm -rf "$FASTTEST_DATA"/{{meta,}data,user_files} ||:
+        rm -rf "$FASTTEST_DATA"/{{meta,}data,user_files,coordination} ||:
 
         start_server
 

src/Coordination/Changelog.cpp

@@ -0,0 +1,557 @@
+#include <Coordination/Changelog.h>
+#include <IO/WriteHelpers.h>
+#include <IO/ReadHelpers.h>
+#include <IO/ReadBufferFromFile.h>
+#include <filesystem>
+#include <boost/algorithm/string/split.hpp>
+#include <boost/algorithm/string/join.hpp>
+#include <boost/algorithm/string/trim.hpp>
+#include <Common/Exception.h>
+#include <Common/SipHash.h>
+#include <common/logger_useful.h>
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int CHECKSUM_DOESNT_MATCH;
+    extern const int CORRUPTED_DATA;
+    extern const int UNKNOWN_FORMAT_VERSION;
+    extern const int LOGICAL_ERROR;
+}
+
+namespace
+{
+
+constexpr auto DEFAULT_PREFIX = "changelog";
+
+std::string formatChangelogPath(const std::string & prefix, const ChangelogFileDescription & name)
+{
+    std::filesystem::path path(prefix);
+    path /= std::filesystem::path(name.prefix + "_" + std::to_string(name.from_log_index) + "_" + std::to_string(name.to_log_index) + ".bin");
+    return path;
+}
+
+ChangelogFileDescription getChangelogFileDescription(const std::string & path_str)
+{
+    std::filesystem::path path(path_str);
+    std::string filename = path.stem();
+    Strings filename_parts;
+    boost::split(filename_parts, filename, boost::is_any_of("_"));
+    if (filename_parts.size() < 3)
+        throw Exception(ErrorCodes::CORRUPTED_DATA, "Invalid changelog {}", path_str);
+
+    ChangelogFileDescription result;
+    result.prefix = filename_parts[0];
+    result.from_log_index = parse<size_t>(filename_parts[1]);
+    result.to_log_index = parse<size_t>(filename_parts[2]);
+    result.path = path_str;
+    return result;
+}
+
+LogEntryPtr makeClone(const LogEntryPtr & entry)
+{
+    return cs_new<nuraft::log_entry>(entry->get_term(), nuraft::buffer::clone(entry->get_buf()), entry->get_val_type());
+}
+
+Checksum computeRecordChecksum(const ChangelogRecord & record)
+{
+    SipHash hash;
+    hash.update(record.header.version);
+    hash.update(record.header.index);
+    hash.update(record.header.term);
+    hash.update(record.header.value_type);
+    hash.update(record.header.blob_size);
+    if (record.header.blob_size != 0)
+        hash.update(reinterpret_cast<char *>(record.blob->data_begin()), record.blob->size());
+    return hash.get64();
+}
+
+}
+
+class ChangelogWriter
+{
+public:
+    ChangelogWriter(const std::string & filepath_, WriteMode mode, size_t start_index_)
+        : filepath(filepath_)
+        , plain_buf(filepath, DBMS_DEFAULT_BUFFER_SIZE, mode == WriteMode::Rewrite ? -1 : (O_APPEND | O_CREAT | O_WRONLY))
+        , start_index(start_index_)
+    {}
+
+
+    off_t appendRecord(ChangelogRecord && record, bool sync)
+    {
+        off_t result = plain_buf.count();
+        writeIntBinary(computeRecordChecksum(record), plain_buf);
+
+        writeIntBinary(record.header.version, plain_buf);
+        writeIntBinary(record.header.index, plain_buf);
+        writeIntBinary(record.header.term, plain_buf);
+        writeIntBinary(record.header.value_type, plain_buf);
+        writeIntBinary(record.header.blob_size, plain_buf);
+
+        if (record.header.blob_size != 0)
+            plain_buf.write(reinterpret_cast<char *>(record.blob->data_begin()), record.blob->size());
+
+        entries_written++;
+
+        if (sync)
+            plain_buf.sync();
+        return result;
+    }
+
+    void truncateToLength(off_t new_length)
+    {
+        flush();
+        plain_buf.truncate(new_length);
+        plain_buf.seek(new_length, SEEK_SET);
+    }
+
+    void flush()
+    {
+        plain_buf.sync();
+    }
+
+    size_t getEntriesWritten() const
+    {
+        return entries_written;
+    }
+
+    void setEntriesWritten(size_t entries_written_)
+    {
+        entries_written = entries_written_;
+    }
+
+    size_t getStartIndex() const
+    {
+        return start_index;
+    }
+
+    void setStartIndex(size_t start_index_)
+    {
+        start_index = start_index_;
+    }
+
+private:
+    std::string filepath;
+    WriteBufferFromFile plain_buf;
+    size_t entries_written = 0;
+    size_t start_index;
+};
+
+struct ChangelogReadResult
+{
+    size_t entries_read;
+    off_t last_position;
+    bool error;
+};
+
+class ChangelogReader
+{
+public:
+    explicit ChangelogReader(const std::string & filepath_)
+        : filepath(filepath_)
+        , read_buf(filepath)
+    {}
+
+    ChangelogReadResult readChangelog(IndexToLogEntry & logs, size_t start_log_index, IndexToOffset & index_to_offset, Poco::Logger * log)
+    {
+        size_t previous_index = 0;
+        ChangelogReadResult result{};
+        try
+        {
+            while (!read_buf.eof())
+            {
+                result.last_position = read_buf.count();
+                Checksum record_checksum;
+                readIntBinary(record_checksum, read_buf);
+
+                /// Initialization is required, otherwise checksums may fail
+                ChangelogRecord record;
+                readIntBinary(record.header.version, read_buf);
+                readIntBinary(record.header.index, read_buf);
+                readIntBinary(record.header.term, read_buf);
+                readIntBinary(record.header.value_type, read_buf);
+                readIntBinary(record.header.blob_size, read_buf);
+
+                if (record.header.version > CURRENT_CHANGELOG_VERSION)
+                    throw Exception(ErrorCodes::UNKNOWN_FORMAT_VERSION, "Unsupported changelog version {} on path {}", record.header.version, filepath);
+
+                if (record.header.blob_size != 0)
+                {
+                    auto buffer = nuraft::buffer::alloc(record.header.blob_size);
+                    auto * buffer_begin = reinterpret_cast<char *>(buffer->data_begin());
+                    read_buf.readStrict(buffer_begin, record.header.blob_size);
+                    record.blob = buffer;
+                }
+                else
+                    record.blob = nullptr;
+
+                if (previous_index != 0 && previous_index + 1 != record.header.index)
+                    throw Exception(ErrorCodes::CORRUPTED_DATA, "Previous log entry {}, next log entry {}, seems like some entries skipped", previous_index, record.header.index);
+
+                previous_index = record.header.index;
+
+                Checksum checksum = computeRecordChecksum(record);
+                if (checksum != record_checksum)
+                {
+                    throw Exception(ErrorCodes::CHECKSUM_DOESNT_MATCH,
+                                    "Checksums doesn't match for log {} (version {}), index {}, blob_size {}",
+                                    filepath, record.header.version, record.header.index, record.header.blob_size);
+                }
+
+                if (logs.count(record.header.index) != 0)
+                    throw Exception(ErrorCodes::CORRUPTED_DATA, "Duplicated index id {} in log {}", record.header.index, filepath);
+
+                result.entries_read += 1;
+
+                if (record.header.index < start_log_index)
+                    continue;
+
+                auto log_entry = nuraft::cs_new<nuraft::log_entry>(record.header.term, record.blob, record.header.value_type);
+
+                logs.emplace(record.header.index, log_entry);
+                index_to_offset[record.header.index] = result.last_position;
+                if (result.entries_read % 50000 == 0)
+                    LOG_TRACE(log, "Reading changelog from path {}, entries {}", filepath, result.entries_read);
+            }
+        }
+        catch (const Exception & ex)
+        {
+            if (ex.code() == ErrorCodes::UNKNOWN_FORMAT_VERSION)
+                throw ex;
+
+            result.error = true;
+            LOG_WARNING(log, "Cannot completely read changelog on path {}, error: {}", filepath, ex.message());
+        }
+        catch (...)
+        {
+            result.error = true;
+            tryLogCurrentException(log);
+        }
+        LOG_TRACE(log, "Totally read from changelog {} {} entries", filepath, result.entries_read);
+
+        return result;
+    }
+
+private:
+    std::string filepath;
+    ReadBufferFromFile read_buf;
+};
+
+Changelog::Changelog(const std::string & changelogs_dir_, size_t rotate_interval_, Poco::Logger * log_)
+    : changelogs_dir(changelogs_dir_)
+    , rotate_interval(rotate_interval_)
+    , log(log_)
+{
+    namespace fs = std::filesystem;
+    if (!fs::exists(changelogs_dir))
+        fs::create_directories(changelogs_dir);
+
+    for (const auto & p : fs::directory_iterator(changelogs_dir))
+    {
+        auto file_description = getChangelogFileDescription(p.path());
+        existing_changelogs[file_description.from_log_index] = file_description;
+    }
+}
+
+void Changelog::readChangelogAndInitWriter(size_t from_log_index)
+{
+    start_index = from_log_index == 0 ? 1 : from_log_index;
+    size_t total_read = 0;
+    size_t entries_in_last = 0;
+    size_t incomplete_log_index = 0;
+    ChangelogReadResult result{};
+
+    bool started = false;
+    for (const auto & [changelog_start_index, changelog_description] : existing_changelogs)
+    {
+        entries_in_last = changelog_description.to_log_index - changelog_description.from_log_index + 1;
+
+        if (changelog_description.to_log_index >= from_log_index)
+        {
+            if (!started)
+            {
+                if (changelog_description.from_log_index > start_index)
+                    throw Exception(ErrorCodes::CORRUPTED_DATA, "Cannot read changelog from index {}, smallest available index {}", start_index, changelog_description.from_log_index);
+                started = true;
+            }
+
+            ChangelogReader reader(changelog_description.path);
+            result = reader.readChangelog(logs, from_log_index, index_to_start_pos, log);
+            total_read += result.entries_read;
+
+            /// May happen after truncate, crash or simply unfinished log
+            if (result.entries_read < entries_in_last)
+            {
+                incomplete_log_index = changelog_start_index;
+                break;
+            }
+        }
+    }
+
+    if (!started && start_index != 1)
+        throw Exception(ErrorCodes::CORRUPTED_DATA, "Required to read data from {}, but we don't have any active changelogs", from_log_index);
+
+    if (incomplete_log_index != 0)
+    {
+        /// All subsequent logs shouldn't exist. But they may exist if we crashed after writeAt started. Remove them.
+        for (auto itr = existing_changelogs.upper_bound(incomplete_log_index); itr != existing_changelogs.end();)
+        {
+            LOG_WARNING(log, "Removing changelog {}, because it's goes after broken changelog entry", itr->second.path);
+            std::filesystem::remove(itr->second.path);
+            itr = existing_changelogs.erase(itr);
+        }
+
+        /// Continue to write into existing log
+        if (!existing_changelogs.empty())
+        {
+            auto description = existing_changelogs.rbegin()->second;
+            LOG_TRACE(log, "Continue to write into {}", description.path);
+            current_writer = std::make_unique<ChangelogWriter>(description.path, WriteMode::Append, description.from_log_index);
+            current_writer->setEntriesWritten(result.entries_read);
+
+            /// Truncate all broken entries from log
+            if (result.error)
+            {
+                LOG_WARNING(log, "Read finished with error, truncating all broken log entries");
+                current_writer->truncateToLength(result.last_position);
+            }
+        }
+    }
+
+    /// Start new log if we don't initialize writer from previous log
+    if (!current_writer)
+        rotate(start_index + total_read);
+}
+
+void Changelog::rotate(size_t new_start_log_index)
+{
+    //// doesn't exist on init
+    if (current_writer)
+        current_writer->flush();
+
+    ChangelogFileDescription new_description;
+    new_description.prefix = DEFAULT_PREFIX;
+    new_description.from_log_index = new_start_log_index;
+    new_description.to_log_index = new_start_log_index + rotate_interval - 1;
+
+    new_description.path = formatChangelogPath(changelogs_dir, new_description);
+
+    LOG_TRACE(log, "Starting new changelog {}", new_description.path);
+    existing_changelogs[new_start_log_index] = new_description;
+    current_writer = std::make_unique<ChangelogWriter>(new_description.path, WriteMode::Rewrite, new_start_log_index);
+}
+
+ChangelogRecord Changelog::buildRecord(size_t index, const LogEntryPtr & log_entry)
+{
+    ChangelogRecord record;
+    record.header.version = ChangelogVersion::V0;
+    record.header.index = index;
+    record.header.term = log_entry->get_term();
+    record.header.value_type = log_entry->get_val_type();
+    auto buffer = log_entry->get_buf_ptr();
+    if (buffer)
+        record.header.blob_size = buffer->size();
+    else
+        record.header.blob_size = 0;
+
+    record.blob = buffer;
+
+    return record;
+}
+
+void Changelog::appendEntry(size_t index, const LogEntryPtr & log_entry, bool force_sync)
+{
+    if (!current_writer)
+        throw Exception(ErrorCodes::LOGICAL_ERROR, "Changelog must be initialized before appending records");
+
+    if (logs.empty())
+        start_index = index;
+
+    if (current_writer->getEntriesWritten() == rotate_interval)
+        rotate(index);
+
+    auto offset = current_writer->appendRecord(buildRecord(index, log_entry), force_sync);
+    if (!index_to_start_pos.try_emplace(index, offset).second)
+        throw Exception(ErrorCodes::LOGICAL_ERROR, "Record with index {} already exists", index);
+
+    logs[index] = makeClone(log_entry);
+}
+
+void Changelog::writeAt(size_t index, const LogEntryPtr & log_entry, bool force_sync)
+{
+    if (index_to_start_pos.count(index) == 0)
+        throw Exception(ErrorCodes::LOGICAL_ERROR, "Cannot write at index {} because changelog doesn't contain it", index);
+
+    bool go_to_previous_file = index < current_writer->getStartIndex();
+    if (go_to_previous_file)
+    {
+        auto index_changelog = existing_changelogs.lower_bound(index);
+        ChangelogFileDescription description;
+        if (index_changelog->first == index)
+            description = index_changelog->second;
+        else
+            description = std::prev(index_changelog)->second;
+
+        current_writer = std::make_unique<ChangelogWriter>(description.path, WriteMode::Append, index_changelog->first);
+        current_writer->setEntriesWritten(description.to_log_index - description.from_log_index + 1);
+    }
+
+    auto entries_written = current_writer->getEntriesWritten();
+    current_writer->truncateToLength(index_to_start_pos[index]);
+
+    if (go_to_previous_file)
+    {
+        /// Remove all subsequent files
+        auto to_remove_itr = existing_changelogs.upper_bound(index);
+        for (auto itr = to_remove_itr; itr != existing_changelogs.end();)
+        {
+            std::filesystem::remove(itr->second.path);
+            itr = existing_changelogs.erase(itr);
+        }
+    }
+
+    /// Remove redundant logs from memory
+    for (size_t i = index; ; ++i)
+    {
+        auto log_itr = logs.find(i);
+        if (log_itr == logs.end())
+            break;
+        logs.erase(log_itr);
+        index_to_start_pos.erase(i);
+        entries_written--;
+    }
+
+    current_writer->setEntriesWritten(entries_written);
+
+    appendEntry(index, log_entry, force_sync);
+}
+
+void Changelog::compact(size_t up_to_log_index)
+{
+    for (auto itr = existing_changelogs.begin(); itr != existing_changelogs.end();)
+    {
+        /// Remove all completely outdated changelog files
+        if (itr->second.to_log_index <= up_to_log_index)
+        {
+
+            LOG_INFO(log, "Removing changelog {} because of compaction", itr->second.path);
+            std::erase_if(index_to_start_pos, [right_index = itr->second.to_log_index] (const auto & item) { return item.first <= right_index; });
+            std::filesystem::remove(itr->second.path);
+            itr = existing_changelogs.erase(itr);
+        }
+        else /// Files are ordered, so all subsequent should exist
+            break;
+    }
+    start_index = up_to_log_index + 1;
+    std::erase_if(logs, [up_to_log_index] (const auto & item) { return item.first <= up_to_log_index; });
+}
+
+LogEntryPtr Changelog::getLastEntry() const
+{
+    static LogEntryPtr fake_entry = nuraft::cs_new<nuraft::log_entry>(0, nuraft::buffer::alloc(sizeof(size_t)));
+
+    size_t next_index = getNextEntryIndex() - 1;
+    auto entry = logs.find(next_index);
+    if (entry == logs.end())
+        return fake_entry;
+
+    return entry->second;
+}
+
+LogEntriesPtr Changelog::getLogEntriesBetween(size_t start, size_t end)
+{
+    LogEntriesPtr ret = nuraft::cs_new<std::vector<nuraft::ptr<nuraft::log_entry>>>();
+
+    ret->resize(end - start);
+    size_t result_pos = 0;
+    for (size_t i = start; i < end; ++i)
+    {
+        (*ret)[result_pos] = entryAt(i);
+        result_pos++;
+    }
+    return ret;
+}
+
+LogEntryPtr Changelog::entryAt(size_t index)
+{
+    nuraft::ptr<nuraft::log_entry> src = nullptr;
+    auto entry = logs.find(index);
+    if (entry == logs.end())
+        return nullptr;
+
+    src = entry->second;
+    return src;
+}
+
+nuraft::ptr<nuraft::buffer> Changelog::serializeEntriesToBuffer(size_t index, int32_t count)
+{
+    std::vector<nuraft::ptr<nuraft::buffer>> returned_logs;
+
+    size_t size_total = 0;
+    for (size_t i = index; i < index + count; ++i)
+    {
+        auto entry = logs.find(i);
+        if (entry == logs.end())
+            throw Exception(ErrorCodes::LOGICAL_ERROR, "Don't have log entry {}", i);
+
+        nuraft::ptr<nuraft::buffer> buf = entry->second->serialize();
+        size_total += buf->size();
+        returned_logs.push_back(buf);
+    }
+
+    nuraft::ptr<nuraft::buffer> buf_out = nuraft::buffer::alloc(sizeof(int32_t) + count * sizeof(int32_t) + size_total);
+    buf_out->pos(0);
+    buf_out->put(static_cast<int32_t>(count));
+
+    for (auto & entry : returned_logs)
+    {
+        nuraft::ptr<nuraft::buffer> & bb = entry;
+        buf_out->put(static_cast<int32_t>(bb->size()));
+        buf_out->put(*bb);
+    }
+    return buf_out;
+}
+
+void Changelog::applyEntriesFromBuffer(size_t index, nuraft::buffer & buffer, bool force_sync)
+{
+    buffer.pos(0);
+    int num_logs = buffer.get_int();
+
+    for (int i = 0; i < num_logs; ++i)
+    {
+        size_t cur_index = index + i;
+        int buf_size = buffer.get_int();
+
+        nuraft::ptr<nuraft::buffer> buf_local = nuraft::buffer::alloc(buf_size);
+        buffer.get(buf_local);
+
+        LogEntryPtr log_entry = nuraft::log_entry::deserialize(*buf_local);
+        if (i == 0 && logs.count(cur_index))
+            writeAt(cur_index, log_entry, force_sync);
+        else
+            appendEntry(cur_index, log_entry, force_sync);
+    }
+}
+
+void Changelog::flush()
+{
+    current_writer->flush();
+}
+
+Changelog::~Changelog()
+{
+    try
+    {
+        if (current_writer)
+            current_writer->flush();
+    }
+    catch (...)
+    {
+        tryLogCurrentException(__PRETTY_FUNCTION__);
+    }
+}
+
+}

src/Coordination/Changelog.h

@@ -0,0 +1,136 @@
+#pragma once
+
+#include <libnuraft/nuraft.hxx> // Y_IGNORE
+#include <city.h>
+#include <IO/WriteBufferFromFile.h>
+#include <IO/HashingWriteBuffer.h>
+#include <Compression/CompressedWriteBuffer.h>
+#include <Disks/IDisk.h>
+
+namespace DB
+{
+
+using Checksum = UInt64;
+
+using LogEntryPtr = nuraft::ptr<nuraft::log_entry>;
+using LogEntries = std::vector<LogEntryPtr>;
+using LogEntriesPtr = nuraft::ptr<LogEntries>;
+using BufferPtr = nuraft::ptr<nuraft::buffer>;
+
+using IndexToOffset = std::unordered_map<size_t, off_t>;
+using IndexToLogEntry = std::unordered_map<size_t, LogEntryPtr>;
+
+enum class ChangelogVersion : uint8_t
+{
+    V0 = 0,
+};
+
+static constexpr auto CURRENT_CHANGELOG_VERSION = ChangelogVersion::V0;
+
+struct ChangelogRecordHeader
+{
+    ChangelogVersion version = CURRENT_CHANGELOG_VERSION;
+    size_t index; /// entry log number
+    size_t term;
+    nuraft::log_val_type value_type;
+    size_t blob_size;
+};
+
+/// Changelog record on disk
+struct ChangelogRecord
+{
+    ChangelogRecordHeader header;
+    nuraft::ptr<nuraft::buffer> blob;
+};
+
+/// changelog_fromindex_toindex.bin
+/// [fromindex, toindex] <- inclusive
+struct ChangelogFileDescription
+{
+    std::string prefix;
+    size_t from_log_index;
+    size_t to_log_index;
+
+    std::string path;
+};
+
+class ChangelogWriter;
+
+/// Simplest changelog with files rotation.
+/// No compression, no metadata, just entries with headers one by one
+/// Able to read broken files/entries and discard them.
+class Changelog
+{
+
+public:
+    Changelog(const std::string & changelogs_dir_, size_t rotate_interval_, Poco::Logger * log_);
+
+    /// Read changelog from files on changelogs_dir_ skipping all entries before from_log_index
+    /// Truncate broken entries, remove files after broken entries.
+    void readChangelogAndInitWriter(size_t from_log_index);
+
+    /// Add entry to log with index. Call fsync if force_sync true.
+    void appendEntry(size_t index, const LogEntryPtr & log_entry, bool force_sync);
+
+    /// Write entry at index and truncate all subsequent entries.
+    void writeAt(size_t index, const LogEntryPtr & log_entry, bool force_sync);
+
+    /// Remove log files with to_log_index <= up_to_log_index.
+    void compact(size_t up_to_log_index);
+
+    size_t getNextEntryIndex() const
+    {
+        return start_index + logs.size();
+    }
+
+    size_t getStartIndex() const
+    {
+        return start_index;
+    }
+
+    /// Last entry in log, or fake entry with term 0 if log is empty
+    LogEntryPtr getLastEntry() const;
+
+    /// Return log entries between [start, end)
+    LogEntriesPtr getLogEntriesBetween(size_t start_index, size_t end_index);
+
+    /// Return entry at position index
+    LogEntryPtr entryAt(size_t index);
+
+    /// Serialize entries from index into buffer
+    BufferPtr serializeEntriesToBuffer(size_t index, int32_t count);
+
+    /// Apply entries from buffer overriding existing entries
+    void applyEntriesFromBuffer(size_t index, nuraft::buffer & buffer, bool force_sync);
+
+    /// Fsync log to disk
+    void flush();
+
+    size_t size() const
+    {
+        return logs.size();
+    }
+
+    /// Fsync log to disk
+    ~Changelog();
+
+private:
+    /// Pack log_entry into changelog record
+    static ChangelogRecord buildRecord(size_t index, const LogEntryPtr & log_entry);
+
+    /// Starts new file [new_start_log_index, new_start_log_index + rotate_interval]
+    void rotate(size_t new_start_log_index);
+
+private:
+    const std::string changelogs_dir;
+    const size_t rotate_interval;
+    Poco::Logger * log;
+
+    std::map<size_t, ChangelogFileDescription> existing_changelogs;
+    std::unique_ptr<ChangelogWriter> current_writer;
+    IndexToOffset index_to_start_pos;
+    IndexToLogEntry logs;
+    size_t start_index = 0;
+};
+
+}

src/Coordination/CoordinationSettings.h

@@ -22,13 +22,15 @@ struct Settings;
     M(Milliseconds, heart_beat_interval_ms, 500, "Heartbeat interval between quorum nodes", 0) \
     M(Milliseconds, election_timeout_lower_bound_ms, 1000, "Lower bound of election timer (avoid too often leader elections)", 0) \
     M(Milliseconds, election_timeout_upper_bound_ms, 2000, "Lower bound of election timer (avoid too often leader elections)", 0) \
-    M(UInt64, reserved_log_items, 5000, "How many log items to store (don't remove during compaction)", 0) \
-    M(UInt64, snapshot_distance, 5000, "How many log items we have to collect to write new snapshot", 0) \
+    M(UInt64, reserved_log_items, 50000, "How many log items to store (don't remove during compaction)", 0) \
+    M(UInt64, snapshot_distance, 100000, "How many log items we have to collect to write new snapshot", 0) \
     M(UInt64, max_stored_snapshots, 3, "How many snapshots we want to store", 0) \
     M(Bool, auto_forwarding, true, "Allow to forward write requests from followers to leader", 0) \
     M(Milliseconds, shutdown_timeout, 5000, "How many time we will until RAFT shutdown", 0) \
     M(Milliseconds, startup_timeout, 30000, "How many time we will until RAFT to start", 0) \
-    M(LogsLevel, raft_logs_level, LogsLevel::information, "Log internal RAFT logs into main server log level. Valid values: 'trace', 'debug', 'information', 'warning', 'error', 'fatal', 'none'", 0)
+    M(LogsLevel, raft_logs_level, LogsLevel::information, "Log internal RAFT logs into main server log level. Valid values: 'trace', 'debug', 'information', 'warning', 'error', 'fatal', 'none'", 0) \
+    M(UInt64, rotate_log_storage_interval, 100000, "How many records will be stored in one log storage file", 0) \
+    M(Bool, force_sync, true, " Call fsync on each change in RAFT changelog", 0)
 
 DECLARE_SETTINGS_TRAITS(CoordinationSettingsTraits, LIST_OF_COORDINATION_SETTINGS)
 

src/Coordination/InMemoryLogStore.cpp

@@ -72,12 +72,12 @@ nuraft::ptr<std::vector<nuraft::ptr<nuraft::log_entry>>> InMemoryLogStore::log_e
 
     ret->resize(end - start);
     size_t cc = 0;
-    for (size_t ii = start; ii < end; ++ii)
+    for (size_t i = start; i < end; ++i)
     {
         nuraft::ptr<nuraft::log_entry> src = nullptr;
         {
             std::lock_guard<std::mutex> l(logs_lock);
-            auto entry = logs.find(ii);
+            auto entry = logs.find(i);
             if (entry == logs.end())
             {
                 entry = logs.find(0);
@@ -152,9 +152,9 @@ void InMemoryLogStore::apply_pack(size_t index, nuraft::buffer & pack)
     pack.pos(0);
     Int32 num_logs = pack.get_int();
 
-    for (Int32 ii = 0; ii < num_logs; ++ii)
+    for (Int32 i = 0; i < num_logs; ++i)
     {
-        size_t cur_idx = index + ii;
+        size_t cur_idx = index + i;
         Int32 buf_size = pack.get_int();
 
         nuraft::ptr<nuraft::buffer> buf_local = nuraft::buffer::alloc(buf_size);

src/Coordination/LoggerWrapper.h

@@ -9,12 +9,26 @@ namespace DB
 
 class LoggerWrapper : public nuraft::logger
 {
+private:
+
+    static inline const std::unordered_map<LogsLevel, Poco::Message::Priority> LEVELS =
+    {
+        {LogsLevel::trace, Poco::Message::Priority::PRIO_TRACE},
+        {LogsLevel::debug, Poco::Message::Priority::PRIO_DEBUG},
+        {LogsLevel::information, Poco::Message::PRIO_INFORMATION},
+        {LogsLevel::warning, Poco::Message::PRIO_WARNING},
+        {LogsLevel::error, Poco::Message::PRIO_ERROR},
+        {LogsLevel::fatal, Poco::Message::PRIO_FATAL}
+    };
+    static inline const int LEVEL_MAX = static_cast<int>(LogsLevel::trace);
+    static inline const int LEVEL_MIN = static_cast<int>(LogsLevel::none);
+
 public:
     LoggerWrapper(const std::string & name, LogsLevel level_)
         : log(&Poco::Logger::get(name))
-        , level(static_cast<int>(level_))
+        , level(level_)
     {
-        log->setLevel(level);
+        log->setLevel(static_cast<int>(LEVELS.at(level)));
     }
 
     void put_details(
@@ -24,24 +38,26 @@ public:
         size_t /* line_number */,
         const std::string & msg) override
     {
-        LOG_IMPL(log, static_cast<DB::LogsLevel>(level_), static_cast<Poco::Message::Priority>(level_), msg);
+        LogsLevel db_level = static_cast<LogsLevel>(level_);
+        LOG_IMPL(log, db_level, LEVELS.at(db_level), msg);
     }
 
     void set_level(int level_) override
     {
-        level_ = std::min(6, std::max(1, level_));
-        log->setLevel(level_);
-        level = level_;
+        level_ = std::min(LEVEL_MAX, std::max(LEVEL_MIN, level_));
+        level = static_cast<LogsLevel>(level_);
+        log->setLevel(static_cast<int>(LEVELS.at(level)));
     }
 
     int get_level() override
     {
-        return level;
+        LogsLevel lvl = level;
+        return static_cast<int>(lvl);
     }
 
 private:
     Poco::Logger * log;
-    std::atomic<int> level;
+    std::atomic<LogsLevel> level;
 };
 
 }

src/Coordination/NuKeeperLogStore.cpp

@@ -0,0 +1,105 @@
+#include <Coordination/NuKeeperLogStore.h>
+
+namespace DB
+{
+
+NuKeeperLogStore::NuKeeperLogStore(const std::string & changelogs_path, size_t rotate_interval_, bool force_sync_)
+    : log(&Poco::Logger::get("NuKeeperLogStore"))
+    , changelog(changelogs_path, rotate_interval_, log)
+    , force_sync(force_sync_)
+{
+}
+
+size_t NuKeeperLogStore::start_index() const
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.getStartIndex();
+}
+
+void NuKeeperLogStore::init(size_t from_log_idx)
+{
+    std::lock_guard lock(changelog_lock);
+    changelog.readChangelogAndInitWriter(from_log_idx);
+}
+
+size_t NuKeeperLogStore::next_slot() const
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.getNextEntryIndex();
+}
+
+nuraft::ptr<nuraft::log_entry> NuKeeperLogStore::last_entry() const
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.getLastEntry();
+}
+
+size_t NuKeeperLogStore::append(nuraft::ptr<nuraft::log_entry> & entry)
+{
+    std::lock_guard lock(changelog_lock);
+    size_t idx = changelog.getNextEntryIndex();
+    changelog.appendEntry(idx, entry, force_sync);
+    return idx;
+}
+
+
+void NuKeeperLogStore::write_at(size_t index, nuraft::ptr<nuraft::log_entry> & entry)
+{
+    std::lock_guard lock(changelog_lock);
+    changelog.writeAt(index, entry, force_sync);
+}
+
+nuraft::ptr<std::vector<nuraft::ptr<nuraft::log_entry>>> NuKeeperLogStore::log_entries(size_t start, size_t end)
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.getLogEntriesBetween(start, end);
+}
+
+nuraft::ptr<nuraft::log_entry> NuKeeperLogStore::entry_at(size_t index)
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.entryAt(index);
+}
+
+size_t NuKeeperLogStore::term_at(size_t index)
+{
+    std::lock_guard lock(changelog_lock);
+    auto entry = changelog.entryAt(index);
+    if (entry)
+        return entry->get_term();
+    return 0;
+}
+
+nuraft::ptr<nuraft::buffer> NuKeeperLogStore::pack(size_t index, int32_t cnt)
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.serializeEntriesToBuffer(index, cnt);
+}
+
+bool NuKeeperLogStore::compact(size_t last_log_index)
+{
+    std::lock_guard lock(changelog_lock);
+    changelog.compact(last_log_index);
+    return true;
+}
+
+bool NuKeeperLogStore::flush()
+{
+    std::lock_guard lock(changelog_lock);
+    changelog.flush();
+    return true;
+}
+
+void NuKeeperLogStore::apply_pack(size_t index, nuraft::buffer & pack)
+{
+    std::lock_guard lock(changelog_lock);
+    changelog.applyEntriesFromBuffer(index, pack, force_sync);
+}
+
+size_t NuKeeperLogStore::size() const
+{
+    std::lock_guard lock(changelog_lock);
+    return changelog.size();
+}
+
+}

src/Coordination/NuKeeperLogStore.h

@@ -0,0 +1,52 @@
+#pragma once
+#include <libnuraft/log_store.hxx> // Y_IGNORE
+#include <map>
+#include <mutex>
+#include <Core/Types.h>
+#include <Coordination/Changelog.h>
+#include <common/logger_useful.h>
+
+namespace DB
+{
+
+class NuKeeperLogStore : public nuraft::log_store
+{
+public:
+    NuKeeperLogStore(const std::string & changelogs_path, size_t rotate_interval_, bool force_sync_);
+
+    void init(size_t from_log_idx);
+
+    size_t start_index() const override;
+
+    size_t next_slot() const override;
+
+    nuraft::ptr<nuraft::log_entry> last_entry() const override;
+
+    size_t append(nuraft::ptr<nuraft::log_entry> & entry) override;
+
+    void write_at(size_t index, nuraft::ptr<nuraft::log_entry> & entry) override;
+
+    nuraft::ptr<std::vector<nuraft::ptr<nuraft::log_entry>>> log_entries(size_t start, size_t end) override;
+
+    nuraft::ptr<nuraft::log_entry> entry_at(size_t index) override;
+
+    size_t term_at(size_t index) override;
+
+    nuraft::ptr<nuraft::buffer> pack(size_t index, int32_t cnt) override;
+
+    void apply_pack(size_t index, nuraft::buffer & pack) override;
+
+    bool compact(size_t last_log_index) override;
+
+    bool flush() override;
+
+    size_t size() const;
+
+private:
+    mutable std::mutex changelog_lock;
+    Poco::Logger * log;
+    Changelog changelog;
+    bool force_sync;
+};
+
+}

src/Coordination/NuKeeperServer.cpp

@@ -1,7 +1,7 @@
 #include <Coordination/NuKeeperServer.h>
 #include <Coordination/LoggerWrapper.h>
 #include <Coordination/NuKeeperStateMachine.h>
-#include <Coordination/InMemoryStateManager.h>
+#include <Coordination/NuKeeperStateManager.h>
 #include <Coordination/WriteBufferFromNuraftBuffer.h>
 #include <Coordination/ReadBufferFromNuraftBuffer.h>
 #include <IO/ReadHelpers.h>
@@ -26,13 +26,16 @@ NuKeeperServer::NuKeeperServer(
     : server_id(server_id_)
     , coordination_settings(coordination_settings_)
     , state_machine(nuraft::cs_new<NuKeeperStateMachine>(responses_queue_, coordination_settings))
-    , state_manager(nuraft::cs_new<InMemoryStateManager>(server_id, "test_keeper_server.raft_configuration", config))
+    , state_manager(nuraft::cs_new<NuKeeperStateManager>(server_id, "test_keeper_server", config, coordination_settings))
     , responses_queue(responses_queue_)
 {
 }
 
 void NuKeeperServer::startup()
 {
+
+    state_manager->loadLogStore(state_machine->last_commit_index());
+
     nuraft::raft_params params;
     params.heart_beat_interval_ = coordination_settings->heart_beat_interval_ms.totalMilliseconds();
     params.election_timeout_lower_bound_ = coordination_settings->election_timeout_lower_bound_ms.totalMilliseconds();
@@ -64,6 +67,7 @@ void NuKeeperServer::startup()
 void NuKeeperServer::shutdown()
 {
     state_machine->shutdownStorage();
+    state_manager->flushLogStore();
     if (!launcher.shutdown(coordination_settings->shutdown_timeout.totalSeconds()))
         LOG_WARNING(&Poco::Logger::get("NuKeeperServer"), "Failed to shutdown RAFT server in {} seconds", 5);
 }
@@ -157,7 +161,7 @@ bool NuKeeperServer::isLeaderAlive() const
 
 nuraft::cb_func::ReturnCode NuKeeperServer::callbackFunc(nuraft::cb_func::Type type, nuraft::cb_func::Param * /* param */)
 {
-    if (type == nuraft::cb_func::Type::BecomeFresh || type == nuraft::cb_func::Type::BecomeLeader)
+    if ((type == nuraft::cb_func::InitialBatchCommited && isLeader()) || type == nuraft::cb_func::BecomeFresh)
     {
         std::unique_lock lock(initialized_mutex);
         initialized_flag = true;

src/Coordination/NuKeeperServer.h

@@ -2,7 +2,7 @@
 
 #include <libnuraft/nuraft.hxx> // Y_IGNORE
 #include <Coordination/InMemoryLogStore.h>
-#include <Coordination/InMemoryStateManager.h>
+#include <Coordination/NuKeeperStateManager.h>
 #include <Coordination/NuKeeperStateMachine.h>
 #include <Coordination/NuKeeperStorage.h>
 #include <Coordination/CoordinationSettings.h>
@@ -20,7 +20,7 @@ private:
 
     nuraft::ptr<NuKeeperStateMachine> state_machine;
 
-    nuraft::ptr<InMemoryStateManager> state_manager;
+    nuraft::ptr<NuKeeperStateManager> state_manager;
 
     nuraft::raft_launcher launcher;
 

src/Coordination/NuKeeperStateMachine.cpp

@@ -46,7 +46,7 @@ NuKeeperStateMachine::NuKeeperStateMachine(ResponsesQueue & responses_queue_, co
     , storage(coordination_settings->dead_session_check_period_ms.totalMilliseconds())
     , responses_queue(responses_queue_)
     , last_committed_idx(0)
-    , log(&Poco::Logger::get("NuRaftStateMachine"))
+    , log(&Poco::Logger::get("NuKeeperStateMachine"))
 {
     LOG_DEBUG(log, "Created nukeeper state machine");
 }

src/Coordination/NuKeeperStateManager.cpp

@@ -1,4 +1,4 @@
-#include <Coordination/InMemoryStateManager.h>
+#include <Coordination/NuKeeperStateManager.h>
 #include <Common/Exception.h>
 
 namespace DB
@@ -9,30 +9,34 @@ namespace ErrorCodes
     extern const int RAFT_ERROR;
 }
 
-InMemoryStateManager::InMemoryStateManager(int server_id_, const std::string & host, int port)
+NuKeeperStateManager::NuKeeperStateManager(int server_id_, const std::string & host, int port, const std::string & logs_path)
     : my_server_id(server_id_)
     , my_port(port)
-    , log_store(nuraft::cs_new<InMemoryLogStore>())
+    , log_store(nuraft::cs_new<NuKeeperLogStore>(logs_path, 5000, false))
     , cluster_config(nuraft::cs_new<nuraft::cluster_config>())
 {
     auto peer_config = nuraft::cs_new<nuraft::srv_config>(my_server_id, host + ":" + std::to_string(port));
     cluster_config->get_servers().push_back(peer_config);
 }
 
-InMemoryStateManager::InMemoryStateManager(
+NuKeeperStateManager::NuKeeperStateManager(
     int my_server_id_,
     const std::string & config_prefix,
-    const Poco::Util::AbstractConfiguration & config)
+    const Poco::Util::AbstractConfiguration & config,
+    const CoordinationSettingsPtr & coordination_settings)
     : my_server_id(my_server_id_)
-    , log_store(nuraft::cs_new<InMemoryLogStore>())
+    , log_store(nuraft::cs_new<NuKeeperLogStore>(
+                    config.getString(config_prefix + ".log_storage_path"),
+                    coordination_settings->rotate_log_storage_interval, coordination_settings->force_sync))
     , cluster_config(nuraft::cs_new<nuraft::cluster_config>())
 {
+
     Poco::Util::AbstractConfiguration::Keys keys;
-    config.keys(config_prefix, keys);
+    config.keys(config_prefix + ".raft_configuration", keys);
 
     for (const auto & server_key : keys)
     {
-        std::string full_prefix = config_prefix + "." + server_key;
+        std::string full_prefix = config_prefix + ".raft_configuration." + server_key;
         int server_id = config.getInt(full_prefix + ".id");
         std::string hostname = config.getString(full_prefix + ".hostname");
         int port = config.getInt(full_prefix + ".port");
@@ -53,13 +57,23 @@ InMemoryStateManager::InMemoryStateManager(
         cluster_config->get_servers().push_back(peer_config);
     }
     if (!my_server_config)
-        throw Exception(ErrorCodes::RAFT_ERROR, "Our server id {} not found in raft_configuration section");
+        throw Exception(ErrorCodes::RAFT_ERROR, "Our server id {} not found in raft_configuration section", my_server_id);
 
     if (start_as_follower_servers.size() == cluster_config->get_servers().size())
         throw Exception(ErrorCodes::RAFT_ERROR, "At least one of servers should be able to start as leader (without <start_as_follower>)");
 }
 
-void InMemoryStateManager::save_config(const nuraft::cluster_config & config)
+void NuKeeperStateManager::loadLogStore(size_t start_log_index)
+{
+    log_store->init(start_log_index);
+}
+
+void NuKeeperStateManager::flushLogStore()
+{
+    log_store->flush();
+}
+
+void NuKeeperStateManager::save_config(const nuraft::cluster_config & config)
 {
     // Just keep in memory in this example.
     // Need to write to disk here, if want to make it durable.
@@ -67,7 +81,7 @@ void InMemoryStateManager::save_config(const nuraft::cluster_config & config)
     cluster_config = nuraft::cluster_config::deserialize(*buf);
 }
 
-void InMemoryStateManager::save_state(const nuraft::srv_state & state)
+void NuKeeperStateManager::save_state(const nuraft::srv_state & state)
 {
      // Just keep in memory in this example.
      // Need to write to disk here, if want to make it durable.

src/Coordination/NuKeeperStateManager.h

@@ -2,25 +2,32 @@
 
 #include <Core/Types.h>
 #include <string>
-#include <Coordination/InMemoryLogStore.h>
+#include <Coordination/NuKeeperLogStore.h>
+#include <Coordination/CoordinationSettings.h>
 #include <libnuraft/nuraft.hxx> // Y_IGNORE
 #include <Poco/Util/AbstractConfiguration.h>
 
 namespace DB
 {
 
-class InMemoryStateManager : public nuraft::state_mgr
+class NuKeeperStateManager : public nuraft::state_mgr
 {
 public:
-    InMemoryStateManager(
+    NuKeeperStateManager(
         int server_id_,
         const std::string & config_prefix,
-        const Poco::Util::AbstractConfiguration & config);
+        const Poco::Util::AbstractConfiguration & config,
+        const CoordinationSettingsPtr & coordination_settings);
 
-    InMemoryStateManager(
+    NuKeeperStateManager(
         int server_id_,
         const std::string & host,
-        int port);
+        int port,
+        const std::string & logs_path);
+
+    void loadLogStore(size_t start_log_index);
+
+    void flushLogStore();
 
     nuraft::ptr<nuraft::cluster_config> load_config() override { return cluster_config; }
 
@@ -49,7 +56,7 @@ private:
     int my_server_id;
     int my_port;
     std::unordered_set<int> start_as_follower_servers;
-    nuraft::ptr<InMemoryLogStore> log_store;
+    nuraft::ptr<NuKeeperLogStore> log_store;
     nuraft::ptr<nuraft::srv_config> my_server_config;
     nuraft::ptr<nuraft::cluster_config> cluster_config;
     nuraft::ptr<nuraft::srv_state> server_state;

src/Coordination/NuKeeperStorage.cpp

@@ -25,10 +25,10 @@ static String parentPath(const String & path)
     return "/";
 }
 
-static String baseName(const String & path)
+static std::string getBaseName(const String & path)
 {
-    auto rslash_pos = path.rfind('/');
-    return path.substr(rslash_pos + 1);
+    size_t basename_start = path.rfind('/');
+    return std::string{&path[basename_start + 1], path.length() - basename_start - 1};
 }
 
 static NuKeeperStorage::ResponsesForSessions processWatchesImpl(const String & path, NuKeeperStorage::Watches & watches, NuKeeperStorage::Watches & list_watches, Coordination::Event event_type)
@@ -167,14 +167,17 @@ struct NuKeeperStorageCreateRequest final : public NuKeeperStorageRequest
 
                 /// Increment sequential number even if node is not sequential
                 ++it->second.seq_num;
-
                 response.path_created = path_created;
+
                 container.emplace(path_created, std::move(created_node));
 
+                auto child_path = getBaseName(path_created);
+                it->second.children.insert(child_path);
+
                 if (request.is_ephemeral)
                     ephemerals[session_id].emplace(path_created);
 
-                undo = [&container, &ephemerals, session_id, path_created, is_ephemeral = request.is_ephemeral, parent_path = it->first]
+                undo = [&container, &ephemerals, session_id, path_created, is_ephemeral = request.is_ephemeral, parent_path = it->first, child_path]
                 {
                     container.erase(path_created);
                     if (is_ephemeral)
@@ -183,6 +186,7 @@ struct NuKeeperStorageCreateRequest final : public NuKeeperStorageRequest
                     --undo_parent.stat.cversion;
                     --undo_parent.stat.numChildren;
                     --undo_parent.seq_num;
+                    undo_parent.children.erase(child_path);
                 };
 
                 ++it->second.stat.cversion;
@@ -250,13 +254,16 @@ struct NuKeeperStorageRemoveRequest final : public NuKeeperStorageRequest
             if (prev_node.is_ephemeral)
                 ephemerals[session_id].erase(request.path);
 
-            container.erase(it);
+            auto child_basename = getBaseName(it->first);
             auto & parent = container.at(parentPath(request.path));
             --parent.stat.numChildren;
             ++parent.stat.cversion;
+            parent.children.erase(child_basename);
             response.error = Coordination::Error::ZOK;
 
-            undo = [prev_node, &container, &ephemerals, session_id, path = request.path]
+            container.erase(it);
+
+            undo = [prev_node, &container, &ephemerals, session_id, path = request.path, child_basename]
             {
                 if (prev_node.is_ephemeral)
                     ephemerals[session_id].emplace(path);
@@ -265,6 +272,7 @@ struct NuKeeperStorageRemoveRequest final : public NuKeeperStorageRequest
                 auto & undo_parent = container.at(parentPath(path));
                 ++undo_parent.stat.numChildren;
                 --undo_parent.stat.cversion;
+                undo_parent.children.insert(child_basename);
             };
         }
 
@@ -370,17 +378,9 @@ struct NuKeeperStorageListRequest final : public NuKeeperStorageRequest
             if (path_prefix.empty())
                 throw DB::Exception("Logical error: path cannot be empty", ErrorCodes::LOGICAL_ERROR);
 
-            if (path_prefix.back() != '/')
-                path_prefix += '/';
+            response.names.insert(response.names.end(), it->second.children.begin(), it->second.children.end());
 
-            /// Fairly inefficient.
-            for (auto child_it = container.upper_bound(path_prefix);
-                 child_it != container.end() && startsWith(child_it->first, path_prefix);
-                ++child_it)
-            {
-                if (parentPath(child_it->first) == request.path)
-                    response.names.emplace_back(baseName(child_it->first));
-            }
+            std::sort(response.names.begin(), response.names.end());
 
             response.stat = it->second.stat;
             response.error = Coordination::Error::ZOK;

src/Coordination/NuKeeperStorage.h

@@ -16,6 +16,7 @@ using namespace DB;
 struct NuKeeperStorageRequest;
 using NuKeeperStorageRequestPtr = std::shared_ptr<NuKeeperStorageRequest>;
 using ResponseCallback = std::function<void(const Coordination::ZooKeeperResponsePtr &)>;
+using ChildrenSet = std::unordered_set<std::string>;
 
 class NuKeeperStorage
 {
@@ -30,6 +31,7 @@ public:
         bool is_sequental = false;
         Coordination::Stat stat{};
         int32_t seq_num = 0;
+        ChildrenSet children{};
     };
 
     struct ResponseForSession
@@ -48,9 +50,9 @@ public:
 
     using RequestsForSessions = std::vector<RequestForSession>;
 
-    using Container = std::map<std::string, Node>;
-    using Ephemerals = std::unordered_map<int64_t, std::unordered_set<String>>;
-    using SessionAndWatcher = std::unordered_map<int64_t, std::unordered_set<String>>;
+    using Container = std::unordered_map<std::string, Node>;
+    using Ephemerals = std::unordered_map<int64_t, std::unordered_set<std::string>>;
+    using SessionAndWatcher = std::unordered_map<int64_t, std::unordered_set<std::string>>;
     using SessionAndTimeout = std::unordered_map<int64_t, long>;
     using SessionIDs = std::vector<int64_t>;
 

src/Coordination/NuKeeperStorageSerializer.cpp

@@ -59,13 +59,16 @@ void NuKeeperStorageSerializer::deserialize(NuKeeperStorage & storage, ReadBuffe
 
     size_t container_size;
     Coordination::read(container_size, in);
-    while (storage.container.size() < container_size)
+
+    size_t current_size = 0;
+    while (current_size < container_size)
     {
         std::string path;
         Coordination::read(path, in);
         NuKeeperStorage::Node node;
         readNode(node, in);
         storage.container[path] = node;
+        current_size++;
     }
     size_t ephemerals_size;
     Coordination::read(ephemerals_size, in);

src/Coordination/tests/gtest_for_build.cpp

@@ -6,9 +6,10 @@
 #endif
 
 #if USE_NURAFT
-
+#include <Poco/ConsoleChannel.h>
+#include <Poco/Logger.h>
 #include <Coordination/InMemoryLogStore.h>
-#include <Coordination/InMemoryStateManager.h>
+#include <Coordination/NuKeeperStateManager.h>
 #include <Coordination/NuKeeperStorageSerializer.h>
 #include <Coordination/SummingStateMachine.h>
 #include <Coordination/NuKeeperStateMachine.h>
@@ -20,9 +21,35 @@
 #include <Common/ZooKeeper/ZooKeeperCommon.h>
 #include <Common/ZooKeeper/ZooKeeperIO.h>
 #include <Common/Exception.h>
+#include <common/logger_useful.h>
 #include <libnuraft/nuraft.hxx> // Y_IGNORE
 #include <thread>
+#include <Coordination/NuKeeperLogStore.h>
+#include <Coordination/Changelog.h>
+#include <filesystem>
 
+namespace fs = std::filesystem;
+struct ChangelogDirTest
+{
+    std::string path;
+    bool drop;
+    explicit ChangelogDirTest(std::string path_, bool drop_ = true)
+        : path(path_)
+        , drop(drop_)
+    {
+        if (fs::exists(path))
+        {
+            EXPECT_TRUE(false) << "Path " << path << " already exists, remove it to run test";
+        }
+        fs::create_directory(path);
+    }
+
+    ~ChangelogDirTest()
+    {
+        if (fs::exists(path) && drop)
+            fs::remove_all(path);
+    }
+};
 
 TEST(CoordinationTest, BuildTest)
 {
@@ -67,14 +94,15 @@ TEST(CoordinationTest, BufferSerde)
 template <typename StateMachine>
 struct SimpliestRaftServer
 {
-    SimpliestRaftServer(int server_id_, const std::string & hostname_, int port_)
+    SimpliestRaftServer(int server_id_, const std::string & hostname_, int port_, const std::string & logs_path)
         : server_id(server_id_)
         , hostname(hostname_)
         , port(port_)
         , endpoint(hostname + ":" + std::to_string(port))
         , state_machine(nuraft::cs_new<StateMachine>())
-        , state_manager(nuraft::cs_new<DB::InMemoryStateManager>(server_id, hostname, port))
+        , state_manager(nuraft::cs_new<DB::NuKeeperStateManager>(server_id, hostname, port, logs_path))
     {
+        state_manager->loadLogStore(1);
         nuraft::raft_params params;
         params.heart_beat_interval_ = 100;
         params.election_timeout_lower_bound_ = 200;
@@ -90,10 +118,10 @@ struct SimpliestRaftServer
 
         if (!raft_instance)
         {
-            std::cerr << "Failed to initialize launcher (see the message "
-                         "in the log file)." << std::endl;
+            std::cerr << "Failed to initialize launcher" << std::endl;
             exit(-1);
         }
+
         std::cout << "init Raft instance " << server_id;
         for (size_t ii = 0; ii < 20; ++ii)
         {
@@ -123,7 +151,7 @@ struct SimpliestRaftServer
     nuraft::ptr<StateMachine> state_machine;
 
     // State manager.
-    nuraft::ptr<nuraft::state_mgr> state_manager;
+    nuraft::ptr<DB::NuKeeperStateManager> state_manager;
 
     // Raft launcher.
     nuraft::raft_launcher launcher;
@@ -134,11 +162,10 @@ struct SimpliestRaftServer
 
 using SummingRaftServer = SimpliestRaftServer<DB::SummingStateMachine>;
 
-nuraft::ptr<nuraft::buffer> getLogEntry(int64_t number)
+nuraft::ptr<nuraft::buffer> getBuffer(int64_t number)
 {
     nuraft::ptr<nuraft::buffer> ret = nuraft::buffer::alloc(sizeof(number));
     nuraft::buffer_serializer bs(ret);
-    // WARNING: We don't consider endian-safety in this example.
     bs.put_raw(&number, sizeof(number));
     return ret;
 }
@@ -146,12 +173,13 @@ nuraft::ptr<nuraft::buffer> getLogEntry(int64_t number)
 
 TEST(CoordinationTest, TestSummingRaft1)
 {
-    SummingRaftServer s1(1, "localhost", 44444);
+    ChangelogDirTest test("./logs");
+    SummingRaftServer s1(1, "localhost", 44444, "./logs");
 
     /// Single node is leader
     EXPECT_EQ(s1.raft_instance->get_leader(), 1);
 
-    auto entry1 = getLogEntry(143);
+    auto entry1 = getBuffer(143);
     auto ret = s1.raft_instance->append_entries({entry1});
     EXPECT_TRUE(ret->get_accepted()) << "failed to replicate: entry 1" << ret->get_result_code();
     EXPECT_EQ(ret->get_result_code(), nuraft::cmd_result_code::OK) << "failed to replicate: entry 1" << ret->get_result_code();
@@ -169,17 +197,23 @@ TEST(CoordinationTest, TestSummingRaft1)
 
 TEST(CoordinationTest, TestSummingRaft3)
 {
-    SummingRaftServer s1(1, "localhost", 44444);
-    SummingRaftServer s2(2, "localhost", 44445);
-    SummingRaftServer s3(3, "localhost", 44446);
+    ChangelogDirTest test1("./logs1");
+    SummingRaftServer s1(1, "localhost", 44444, "./logs1");
+    ChangelogDirTest test2("./logs2");
+    SummingRaftServer s2(2, "localhost", 44445, "./logs2");
+    ChangelogDirTest test3("./logs3");
+    SummingRaftServer s3(3, "localhost", 44446, "./logs3");
 
-    nuraft::srv_config first_config(1, "localhost:44444");
+    nuraft::srv_config first_config(1, 0, "localhost:44444", "", false, 0);
     auto ret1 = s2.raft_instance->add_srv(first_config);
-    if (!ret1->get_accepted())
+    while (!ret1->get_accepted())
     {
+
         std::cout << "failed to add server: "
                   << ret1->get_result_str() << std::endl;
-        EXPECT_TRUE(false);
+
+        std::this_thread::sleep_for(std::chrono::milliseconds(100));
+        ret1 = s2.raft_instance->add_srv(first_config);
     }
 
     while (s1.raft_instance->get_leader() != 2)
@@ -188,13 +222,15 @@ TEST(CoordinationTest, TestSummingRaft3)
         std::this_thread::sleep_for(std::chrono::milliseconds(100));
     }
 
-    nuraft::srv_config third_config(3, "localhost:44446");
+    nuraft::srv_config third_config(3, 0, "localhost:44446", "", false, 0);
     auto ret3 = s2.raft_instance->add_srv(third_config);
     if (!ret3->get_accepted())
     {
         std::cout << "failed to add server: "
                   << ret3->get_result_str() << std::endl;
-        EXPECT_TRUE(false);
+
+        std::this_thread::sleep_for(std::chrono::milliseconds(100));
+        ret3 = s2.raft_instance->add_srv(third_config);
     }
 
     while (s3.raft_instance->get_leader() != 2)
@@ -209,10 +245,13 @@ TEST(CoordinationTest, TestSummingRaft3)
     EXPECT_EQ(s3.raft_instance->get_leader(), 2);
 
     std::cerr << "Starting to add entries\n";
-    auto entry = getLogEntry(1);
+    auto entry = getBuffer(1);
     auto ret = s2.raft_instance->append_entries({entry});
-    EXPECT_TRUE(ret->get_accepted()) << "failed to replicate: entry 1" << ret->get_result_code();
-    EXPECT_EQ(ret->get_result_code(), nuraft::cmd_result_code::OK) << "failed to replicate: entry 1" << ret->get_result_code();
+    while (!ret->get_accepted() || ret->get_result_code() != nuraft::cmd_result_code::OK)
+    {
+        std::cerr <<  ret->get_accepted() << "failed to replicate: entry 1" << ret->get_result_code() << std::endl;
+        ret = s2.raft_instance->append_entries({entry});
+    }
 
     while (s1.state_machine->getValue() != 1)
     {
@@ -236,7 +275,7 @@ TEST(CoordinationTest, TestSummingRaft3)
     EXPECT_EQ(s2.state_machine->getValue(), 1);
     EXPECT_EQ(s3.state_machine->getValue(), 1);
 
-    auto non_leader_entry = getLogEntry(3);
+    auto non_leader_entry = getBuffer(3);
     auto ret_non_leader1 = s1.raft_instance->append_entries({non_leader_entry});
 
     EXPECT_FALSE(ret_non_leader1->get_accepted());
@@ -245,10 +284,13 @@ TEST(CoordinationTest, TestSummingRaft3)
 
     EXPECT_FALSE(ret_non_leader3->get_accepted());
 
-    auto leader_entry = getLogEntry(77);
+    auto leader_entry = getBuffer(77);
     auto ret_leader = s2.raft_instance->append_entries({leader_entry});
-    EXPECT_TRUE(ret_leader->get_accepted()) << "failed to replicate: entry 78" << ret_leader->get_result_code();
-    EXPECT_EQ(ret_leader->get_result_code(), nuraft::cmd_result_code::OK) << "failed to replicate: entry 78" << ret_leader->get_result_code();
+    while (!ret_leader->get_accepted() || ret_leader->get_result_code() != nuraft::cmd_result_code::OK)
+    {
+        std::cerr << "failed to replicate: entry 78" << ret_leader->get_result_code() << std::endl;
+        ret_leader = s2.raft_instance->append_entries({leader_entry});
+    }
 
     while (s1.state_machine->getValue() != 78)
     {
@@ -333,4 +375,586 @@ TEST(CoordinationTest, TestStorageSerialization)
     EXPECT_EQ(new_storage.ephemerals[1].size(), 1);
 }
 
+DB::LogEntryPtr getLogEntry(const std::string & s, size_t term)
+{
+    DB::WriteBufferFromNuraftBuffer bufwriter;
+    writeText(s, bufwriter);
+    return nuraft::cs_new<nuraft::log_entry>(term, bufwriter.getBuffer());
+}
+
+TEST(CoordinationTest, ChangelogTestSimple)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+    auto entry = getLogEntry("hello world", 77);
+    changelog.append(entry);
+    EXPECT_EQ(changelog.next_slot(), 2);
+    EXPECT_EQ(changelog.start_index(), 1);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 77);
+    EXPECT_EQ(changelog.entry_at(1)->get_term(), 77);
+    EXPECT_EQ(changelog.log_entries(1, 2)->size(), 1);
+}
+
+TEST(CoordinationTest, ChangelogTestFile)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+    auto entry = getLogEntry("hello world", 77);
+    changelog.append(entry);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    for (const auto & p : fs::directory_iterator("./logs"))
+        EXPECT_EQ(p.path(), "./logs/changelog_1_5.bin");
+
+    changelog.append(entry);
+    changelog.append(entry);
+    changelog.append(entry);
+    changelog.append(entry);
+    changelog.append(entry);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+}
+
+TEST(CoordinationTest, ChangelogReadWrite)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 1000, true);
+    changelog.init(1);
+    for (size_t i = 0; i < 10; ++i)
+    {
+        auto entry = getLogEntry("hello world", i * 10);
+        changelog.append(entry);
+    }
+    EXPECT_EQ(changelog.size(), 10);
+    DB::NuKeeperLogStore changelog_reader("./logs", 1000, true);
+    changelog_reader.init(1);
+    EXPECT_EQ(changelog_reader.size(), 10);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), changelog.last_entry()->get_term());
+    EXPECT_EQ(changelog_reader.start_index(), changelog.start_index());
+    EXPECT_EQ(changelog_reader.next_slot(), changelog.next_slot());
+
+    for (size_t i = 0; i < 10; ++i)
+        EXPECT_EQ(changelog_reader.entry_at(i + 1)->get_term(), changelog.entry_at(i + 1)->get_term());
+
+    auto entries_from_range_read = changelog_reader.log_entries(1, 11);
+    auto entries_from_range = changelog.log_entries(1, 11);
+    EXPECT_EQ(entries_from_range_read->size(), entries_from_range->size());
+    EXPECT_EQ(10, entries_from_range->size());
+}
+
+TEST(CoordinationTest, ChangelogWriteAt)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 1000, true);
+    changelog.init(1);
+    for (size_t i = 0; i < 10; ++i)
+    {
+        auto entry = getLogEntry("hello world", i * 10);
+        changelog.append(entry);
+    }
+    EXPECT_EQ(changelog.size(), 10);
+
+    auto entry = getLogEntry("writer", 77);
+    changelog.write_at(7, entry);
+    EXPECT_EQ(changelog.size(), 7);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 77);
+    EXPECT_EQ(changelog.entry_at(7)->get_term(), 77);
+    EXPECT_EQ(changelog.next_slot(), 8);
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 1000, true);
+    changelog_reader.init(1);
+
+    EXPECT_EQ(changelog_reader.size(), changelog.size());
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), changelog.last_entry()->get_term());
+    EXPECT_EQ(changelog_reader.start_index(), changelog.start_index());
+    EXPECT_EQ(changelog_reader.next_slot(), changelog.next_slot());
+}
+
+
+TEST(CoordinationTest, ChangelogTestAppendAfterRead)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+    for (size_t i = 0; i < 7; ++i)
+    {
+        auto entry = getLogEntry("hello world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_EQ(changelog.size(), 7);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 5, true);
+    changelog_reader.init(1);
+
+    EXPECT_EQ(changelog_reader.size(), 7);
+    for (size_t i = 7; i < 10; ++i)
+    {
+        auto entry = getLogEntry("hello world", i * 10);
+        changelog_reader.append(entry);
+    }
+    EXPECT_EQ(changelog_reader.size(), 10);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+
+    size_t logs_count = 0;
+    for (const auto & _ [[maybe_unused]]: fs::directory_iterator("./logs"))
+        logs_count++;
+
+    EXPECT_EQ(logs_count, 2);
+
+    auto entry = getLogEntry("someentry", 77);
+    changelog_reader.append(entry);
+    EXPECT_EQ(changelog_reader.size(), 11);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+
+    logs_count = 0;
+    for (const auto & _ [[maybe_unused]]: fs::directory_iterator("./logs"))
+        logs_count++;
+
+    EXPECT_EQ(logs_count, 3);
+}
+
+TEST(CoordinationTest, ChangelogTestCompaction)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 3; ++i)
+    {
+        auto entry = getLogEntry("hello world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_EQ(changelog.size(), 3);
+
+    changelog.compact(2);
+
+    EXPECT_EQ(changelog.size(), 1);
+    EXPECT_EQ(changelog.start_index(), 3);
+    EXPECT_EQ(changelog.next_slot(), 4);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 20);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+
+    auto e1 = getLogEntry("hello world", 30);
+    changelog.append(e1);
+    auto e2 = getLogEntry("hello world", 40);
+    changelog.append(e2);
+    auto e3 = getLogEntry("hello world", 50);
+    changelog.append(e3);
+    auto e4 = getLogEntry("hello world", 60);
+    changelog.append(e4);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+
+    changelog.compact(6);
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+
+    EXPECT_EQ(changelog.size(), 1);
+    EXPECT_EQ(changelog.start_index(), 7);
+    EXPECT_EQ(changelog.next_slot(), 8);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 60);
+    /// And we able to read it
+    DB::NuKeeperLogStore changelog_reader("./logs", 5, true);
+    changelog_reader.init(7);
+    EXPECT_EQ(changelog_reader.size(), 1);
+    EXPECT_EQ(changelog_reader.start_index(), 7);
+    EXPECT_EQ(changelog_reader.next_slot(), 8);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), 60);
+}
+
+TEST(CoordinationTest, ChangelogTestBatchOperations)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 100, true);
+    changelog.init(1);
+    for (size_t i = 0; i < 10; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_EQ(changelog.size(), 10);
+
+    auto entries = changelog.pack(1, 5);
+
+    DB::NuKeeperLogStore apply_changelog("./logs", 100, true);
+    apply_changelog.init(1);
+
+    for (size_t i = 0; i < 10; ++i)
+    {
+        EXPECT_EQ(apply_changelog.entry_at(i + 1)->get_term(), i * 10);
+    }
+    EXPECT_EQ(apply_changelog.size(), 10);
+
+    apply_changelog.apply_pack(8, *entries);
+
+    EXPECT_EQ(apply_changelog.size(), 12);
+    EXPECT_EQ(apply_changelog.start_index(), 1);
+    EXPECT_EQ(apply_changelog.next_slot(), 13);
+
+    for (size_t i = 0; i < 7; ++i)
+    {
+        EXPECT_EQ(apply_changelog.entry_at(i + 1)->get_term(), i * 10);
+    }
+
+    EXPECT_EQ(apply_changelog.entry_at(8)->get_term(), 0);
+    EXPECT_EQ(apply_changelog.entry_at(9)->get_term(), 10);
+    EXPECT_EQ(apply_changelog.entry_at(10)->get_term(), 20);
+    EXPECT_EQ(apply_changelog.entry_at(11)->get_term(), 30);
+    EXPECT_EQ(apply_changelog.entry_at(12)->get_term(), 40);
+}
+
+TEST(CoordinationTest, ChangelogTestBatchOperationsEmpty)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 100, true);
+    changelog.init(1);
+    for (size_t i = 0; i < 10; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_EQ(changelog.size(), 10);
+
+    auto entries = changelog.pack(5, 5);
+
+    ChangelogDirTest test1("./logs1");
+    DB::NuKeeperLogStore changelog_new("./logs1", 100, true);
+    changelog_new.init(1);
+    EXPECT_EQ(changelog_new.size(), 0);
+
+    changelog_new.apply_pack(5, *entries);
+
+    EXPECT_EQ(changelog_new.size(), 5);
+    EXPECT_EQ(changelog_new.start_index(), 5);
+    EXPECT_EQ(changelog_new.next_slot(), 10);
+
+    for (size_t i = 4; i < 9; ++i)
+        EXPECT_EQ(changelog_new.entry_at(i + 1)->get_term(), i * 10);
+
+    auto e = getLogEntry("hello_world", 110);
+    changelog_new.append(e);
+    EXPECT_EQ(changelog_new.size(), 6);
+    EXPECT_EQ(changelog_new.start_index(), 5);
+    EXPECT_EQ(changelog_new.next_slot(), 11);
+
+    DB::NuKeeperLogStore changelog_reader("./logs1", 100, true);
+    changelog_reader.init(5);
+}
+
+
+TEST(CoordinationTest, ChangelogTestWriteAtPreviousFile)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 33; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+
+    EXPECT_EQ(changelog.size(), 33);
+
+    auto e1 = getLogEntry("helloworld", 5555);
+    changelog.write_at(7, e1);
+    EXPECT_EQ(changelog.size(), 7);
+    EXPECT_EQ(changelog.start_index(), 1);
+    EXPECT_EQ(changelog.next_slot(), 8);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 5555);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_31_35.bin"));
+
+    DB::NuKeeperLogStore changelog_read("./logs", 5, true);
+    changelog_read.init(1);
+    EXPECT_EQ(changelog_read.size(), 7);
+    EXPECT_EQ(changelog_read.start_index(), 1);
+    EXPECT_EQ(changelog_read.next_slot(), 8);
+    EXPECT_EQ(changelog_read.last_entry()->get_term(), 5555);
+}
+
+TEST(CoordinationTest, ChangelogTestWriteAtFileBorder)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 33; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+
+    EXPECT_EQ(changelog.size(), 33);
+
+    auto e1 = getLogEntry("helloworld", 5555);
+    changelog.write_at(11, e1);
+    EXPECT_EQ(changelog.size(), 11);
+    EXPECT_EQ(changelog.start_index(), 1);
+    EXPECT_EQ(changelog.next_slot(), 12);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 5555);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_31_35.bin"));
+
+    DB::NuKeeperLogStore changelog_read("./logs", 5, true);
+    changelog_read.init(1);
+    EXPECT_EQ(changelog_read.size(), 11);
+    EXPECT_EQ(changelog_read.start_index(), 1);
+    EXPECT_EQ(changelog_read.next_slot(), 12);
+    EXPECT_EQ(changelog_read.last_entry()->get_term(), 5555);
+}
+
+TEST(CoordinationTest, ChangelogTestWriteAtAllFiles)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 33; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+
+    EXPECT_EQ(changelog.size(), 33);
+
+    auto e1 = getLogEntry("helloworld", 5555);
+    changelog.write_at(1, e1);
+    EXPECT_EQ(changelog.size(), 1);
+    EXPECT_EQ(changelog.start_index(), 1);
+    EXPECT_EQ(changelog.next_slot(), 2);
+    EXPECT_EQ(changelog.last_entry()->get_term(), 5555);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_31_35.bin"));
+}
+
+TEST(CoordinationTest, ChangelogTestStartNewLogAfterRead)
+{
+    ChangelogDirTest test("./logs");
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 35; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+    EXPECT_EQ(changelog.size(), 35);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_36_40.bin"));
+
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 5, true);
+    changelog_reader.init(1);
+
+    auto entry = getLogEntry("36_hello_world", 360);
+    changelog_reader.append(entry);
+
+    EXPECT_EQ(changelog_reader.size(), 36);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_36_40.bin"));
+}
+
+
+TEST(CoordinationTest, ChangelogTestReadAfterBrokenTruncate)
+{
+    ChangelogDirTest test("./logs");
+
+    DB::NuKeeperLogStore changelog("./logs", 5, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 35; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", i * 10);
+        changelog.append(entry);
+    }
+    EXPECT_EQ(changelog.size(), 35);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_31_35.bin"));
+
+    DB::WriteBufferFromFile plain_buf("./logs/changelog_11_15.bin", DBMS_DEFAULT_BUFFER_SIZE, O_APPEND | O_CREAT | O_WRONLY);
+    plain_buf.truncate(0);
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 5, true);
+    changelog_reader.init(1);
+
+    EXPECT_EQ(changelog_reader.size(), 10);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), 90);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_31_35.bin"));
+
+    auto entry = getLogEntry("h", 7777);
+    changelog_reader.append(entry);
+    EXPECT_EQ(changelog_reader.size(), 11);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), 7777);
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_5.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_6_10.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_11_15.bin"));
+
+    EXPECT_FALSE(fs::exists("./logs/changelog_16_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_25.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_26_30.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_31_35.bin"));
+
+    DB::NuKeeperLogStore changelog_reader2("./logs", 5, true);
+    changelog_reader2.init(1);
+    EXPECT_EQ(changelog_reader2.size(), 11);
+    EXPECT_EQ(changelog_reader2.last_entry()->get_term(), 7777);
+}
+
+TEST(CoordinationTest, ChangelogTestReadAfterBrokenTruncate2)
+{
+    ChangelogDirTest test("./logs");
+
+    DB::NuKeeperLogStore changelog("./logs", 20, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 35; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", (i + 44) * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_40.bin"));
+
+    DB::WriteBufferFromFile plain_buf("./logs/changelog_1_20.bin", DBMS_DEFAULT_BUFFER_SIZE, O_APPEND | O_CREAT | O_WRONLY);
+    plain_buf.truncate(140);
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 20, true);
+    changelog_reader.init(1);
+
+    EXPECT_EQ(changelog_reader.size(), 2);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), 450);
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_20.bin"));
+    EXPECT_FALSE(fs::exists("./logs/changelog_21_40.bin"));
+    auto entry = getLogEntry("hello_world", 7777);
+    changelog_reader.append(entry);
+    EXPECT_EQ(changelog_reader.size(), 3);
+    EXPECT_EQ(changelog_reader.last_entry()->get_term(), 7777);
+
+
+    DB::NuKeeperLogStore changelog_reader2("./logs", 20, true);
+    changelog_reader2.init(1);
+    EXPECT_EQ(changelog_reader2.size(), 3);
+    EXPECT_EQ(changelog_reader2.last_entry()->get_term(), 7777);
+}
+
+TEST(CoordinationTest, ChangelogTestLostFiles)
+{
+    ChangelogDirTest test("./logs");
+
+    DB::NuKeeperLogStore changelog("./logs", 20, true);
+    changelog.init(1);
+
+    for (size_t i = 0; i < 35; ++i)
+    {
+        auto entry = getLogEntry(std::to_string(i) + "_hello_world", (i + 44) * 10);
+        changelog.append(entry);
+    }
+
+    EXPECT_TRUE(fs::exists("./logs/changelog_1_20.bin"));
+    EXPECT_TRUE(fs::exists("./logs/changelog_21_40.bin"));
+
+    fs::remove("./logs/changelog_1_20.bin");
+
+    DB::NuKeeperLogStore changelog_reader("./logs", 20, true);
+    EXPECT_THROW(changelog_reader.init(5), DB::Exception);
+
+    fs::remove("./logs/changelog_21_40.bin");
+    EXPECT_THROW(changelog_reader.init(3), DB::Exception);
+}
+
+int main(int argc, char ** argv)
+{
+    Poco::AutoPtr<Poco::ConsoleChannel> channel(new Poco::ConsoleChannel(std::cerr));
+    Poco::Logger::root().setChannel(channel);
+    Poco::Logger::root().setLevel("trace");
+    testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}
+
 #endif

src/Server/NuKeeperTCPHandler.cpp

@@ -40,7 +40,7 @@ namespace ErrorCodes
 
 struct PollResult
 {
-    size_t ready_responses_count{0};
+    size_t responses_count{0};
     bool has_requests{false};
     bool error{false};
 };
@@ -70,14 +70,14 @@ struct SocketInterruptablePollWrapper
         if (epollfd < 0)
             throwFromErrno("Cannot epoll_create", ErrorCodes::SYSTEM_ERROR);
 
-        socket_event.events = EPOLLIN | EPOLLERR;
+        socket_event.events = EPOLLIN | EPOLLERR | EPOLLPRI;
         socket_event.data.fd = sockfd;
         if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &socket_event) < 0)
         {
             ::close(epollfd);
             throwFromErrno("Cannot insert socket into epoll queue", ErrorCodes::SYSTEM_ERROR);
         }
-        pipe_event.events = EPOLLIN | EPOLLERR;
+        pipe_event.events = EPOLLIN | EPOLLERR | EPOLLPRI;
         pipe_event.data.fd = pipe.fds_rw[0];
         if (epoll_ctl(epollfd, EPOLL_CTL_ADD, pipe.fds_rw[0], &pipe_event) < 0)
         {
@@ -92,13 +92,24 @@ struct SocketInterruptablePollWrapper
         return pipe.fds_rw[1];
     }
 
-    PollResult poll(Poco::Timespan remaining_time)
+    PollResult poll(Poco::Timespan remaining_time, const std::shared_ptr<ReadBufferFromPocoSocket> & in)
+    {
+
+        bool socket_ready = false;
+        bool fd_ready = false;
+
+        if (in->available() != 0)
+            socket_ready = true;
+
+        if (response_in.available() != 0)
+            fd_ready = true;
+
+        int rc = 0;
+        if (!fd_ready)
         {
-        std::array<int, 2> outputs = {-1, -1};
 #if defined(POCO_HAVE_FD_EPOLL)
-        int rc;
             epoll_event evout[2];
-        memset(evout, 0, sizeof(evout));
+            evout[0].data.fd = evout[1].data.fd = -1;
             do
             {
                 Poco::Timestamp start;
@@ -115,10 +126,13 @@ struct SocketInterruptablePollWrapper
             }
             while (rc < 0 && errno == EINTR);
 
-        if (rc >= 1 && evout[0].events & EPOLLIN)
-            outputs[0] = evout[0].data.fd;
-        if (rc == 2 && evout[1].events & EPOLLIN)
-            outputs[1] = evout[1].data.fd;
+            for (int i = 0; i < rc; ++i)
+            {
+                if (evout[i].data.fd == sockfd)
+                    socket_ready = true;
+                if (evout[i].data.fd == pipe.fds_rw[0])
+                    fd_ready = true;
+            }
 #else
             pollfd poll_buf[2];
             poll_buf[0].fd = sockfd;
@@ -126,7 +140,6 @@ struct SocketInterruptablePollWrapper
             poll_buf[1].fd = pipe.fds_rw[0];
             poll_buf[1].events = POLLIN;
 
-        int rc;
             do
             {
                 Poco::Timestamp start;
@@ -142,47 +155,29 @@ struct SocketInterruptablePollWrapper
                 }
             }
             while (rc < 0 && errno == POCO_EINTR);
+
             if (rc >= 1 && poll_buf[0].revents & POLLIN)
-            outputs[0] = sockfd;
+                socket_ready = true;
             if (rc == 2 && poll_buf[1].revents & POLLIN)
-            outputs[1] = pipe.fds_rw[0];
+                fd_ready = true;
 #endif
+        }
 
         PollResult result{};
-        if (rc < 0)
-        {
-            result.error = true;
-            return result;
-        }
-        else if (rc == 0)
-        {
-            return result;
-        }
-        else
-        {
-            for (auto fd : outputs)
-            {
-                if (fd != -1)
-                {
-                    if (fd == sockfd)
-                        result.has_requests = true;
-                    else
+        result.has_requests = socket_ready;
+        if (fd_ready)
         {
             UInt8 dummy;
-                        do
-                        {
-                            /// All ready responses stored in responses queue,
-                            /// but we have to count amount of ready responses in pipe
-                            /// and process them only. Otherwise states of response_in
-                            /// and response queue will be inconsistent and race condition is possible.
             readIntBinary(dummy, response_in);
-                            result.ready_responses_count++;
-                        }
-                        while (response_in.available());
-                    }
-                }
-            }
+            result.responses_count = 1;
+            auto available = response_in.available();
+            response_in.ignore(available);
+            result.responses_count += available;
         }
+
+        if (rc < 0)
+            result.error = true;
+
         return result;
     }
 
@@ -339,10 +334,8 @@ void NuKeeperTCPHandler::runImpl()
         {
             using namespace std::chrono_literals;
 
-            PollResult result = poll_wrapper->poll(session_timeout);
+            PollResult result = poll_wrapper->poll(session_timeout, in);
             if (result.has_requests && !close_received)
-            {
-                do
             {
                 auto [received_op, received_xid] = receiveRequest();
 
@@ -351,7 +344,6 @@ void NuKeeperTCPHandler::runImpl()
                     LOG_DEBUG(log, "Received close event with xid {} for session id #{}", received_xid, session_id);
                     close_xid = received_xid;
                     close_received = true;
-                        break;
                 }
                 else if (received_op == Coordination::OpNum::Heartbeat)
                 {
@@ -359,23 +351,23 @@ void NuKeeperTCPHandler::runImpl()
                     session_stopwatch.restart();
                 }
             }
-                while (in->available());
-            }
 
             /// Process exact amount of responses from pipe
             /// otherwise state of responses queue and signaling pipe
             /// became inconsistent and race condition is possible.
-            while (result.ready_responses_count != 0)
+            while (result.responses_count != 0)
             {
                 Coordination::ZooKeeperResponsePtr response;
+
                 if (!responses->tryPop(response))
-                    throw Exception(ErrorCodes::LOGICAL_ERROR, "We must have at least {} ready responses, but queue is empty. It's a bug.", result.ready_responses_count);
+                    throw Exception(ErrorCodes::LOGICAL_ERROR, "We must have ready response, but queue is empty. It's a bug.");
 
                 if (response->xid == close_xid)
                 {
                     LOG_DEBUG(log, "Session #{} successfully closed", session_id);
                     return;
                 }
+
                 response->write(*out);
                 if (response->error == Coordination::Error::ZSESSIONEXPIRED)
                 {
@@ -383,7 +375,8 @@ void NuKeeperTCPHandler::runImpl()
                     nu_keeper_storage_dispatcher->finishSession(session_id);
                     return;
                 }
-                result.ready_responses_count--;
+
+                result.responses_count--;
             }
 
             if (result.error)

tests/config/config.d/test_keeper_port.xml

@@ -2,12 +2,15 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>10000</operation_timeout_ms>
             <session_timeout_ms>30000</session_timeout_ms>
             <snapshot_distance>0</snapshot_distance>
             <reserved_log_items>0</reserved_log_items>
+            <force_sync>false</force_sync>
+            <startup_timeout>60000</startup_timeout>
         </coordination_settings>
 
         <raft_configuration>

tests/integration/test_testkeeper_back_to_back/configs/enable_test_keeper.xml

@@ -2,11 +2,13 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>
             <session_timeout_ms>10000</session_timeout_ms>
             <raft_logs_level>trace</raft_logs_level>
+            <force_sync>false</force_sync>
         </coordination_settings>
 
         <raft_configuration>

tests/integration/test_testkeeper_back_to_back/configs/use_test_keeper.xml

@@ -0,0 +1,8 @@
+<yandex>
+    <zookeeper>
+            <node index="1">
+            <host>node1</host>
+            <port>9181</port>
+        </node>
+    </zookeeper>
+</yandex>

tests/integration/test_testkeeper_back_to_back/test.py

@@ -8,27 +8,18 @@ from multiprocessing.dummy import Pool
 
 cluster = ClickHouseCluster(__file__)
 node = cluster.add_instance('node', main_configs=['configs/enable_test_keeper.xml', 'configs/logs_conf.xml'], with_zookeeper=True)
-from kazoo.client import KazooClient, KazooState
-
-_genuine_zk_instance = None
-_fake_zk_instance = None
+from kazoo.client import KazooClient, KazooState, KeeperState
 
 def get_genuine_zk():
-    global _genuine_zk_instance
-    if not _genuine_zk_instance:
     print("Zoo1", cluster.get_instance_ip("zoo1"))
-        _genuine_zk_instance = cluster.get_kazoo_client('zoo1')
-    return _genuine_zk_instance
-
+    return cluster.get_kazoo_client('zoo1')
 
 def get_fake_zk():
-    global _fake_zk_instance
-    if not _fake_zk_instance:
     print("node", cluster.get_instance_ip("node"))
     _fake_zk_instance =  KazooClient(hosts=cluster.get_instance_ip("node") + ":9181", timeout=30.0)
     def reset_last_zxid_listener(state):
         print("Fake zk callback called for state", state)
-            global _fake_zk_instance
+        nonlocal _fake_zk_instance
         if state != KazooState.CONNECTED:
             _fake_zk_instance._reset()
 
@@ -44,6 +35,15 @@ def create_random_path(prefix="", depth=1):
         return prefix
     return create_random_path(os.path.join(prefix, random_string(3)), depth - 1)
 
+def stop_zk(zk):
+    try:
+        if zk:
+            zk.stop()
+            zk.close()
+    except:
+        pass
+
+
 @pytest.fixture(scope="module")
 def started_cluster():
     try:
@@ -53,15 +53,10 @@ def started_cluster():
 
     finally:
         cluster.shutdown()
-        if _genuine_zk_instance:
-            _genuine_zk_instance.stop()
-            _genuine_zk_instance.close()
-        if _fake_zk_instance:
-            _fake_zk_instance.stop()
-            _fake_zk_instance.close()
 
 
 def test_simple_commands(started_cluster):
+    try:
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
 
@@ -75,9 +70,13 @@ def test_simple_commands(started_cluster):
             assert zk.exists("/test_simple_commands/somenode1")
             print(zk.get("/test_simple_commands/somenode1"))
             assert zk.get("/test_simple_commands/somenode1")[0] == b"world"
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 
 def test_sequential_nodes(started_cluster):
+    try:
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
         genuine_zk.create("/test_sequential_nodes")
@@ -91,6 +90,9 @@ def test_sequential_nodes(started_cluster):
         genuine_childs = list(sorted(genuine_zk.get_children("/test_sequential_nodes")))
         fake_childs = list(sorted(fake_zk.get_children("/test_sequential_nodes")))
         assert genuine_childs == fake_childs
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 
 def assert_eq_stats(stat1, stat2):
@@ -102,6 +104,7 @@ def assert_eq_stats(stat1, stat2):
     assert stat1.numChildren == stat2.numChildren
 
 def test_stats(started_cluster):
+    try:
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
         genuine_zk.create("/test_stats_nodes")
@@ -139,8 +142,12 @@ def test_stats(started_cluster):
         print(genuine_stats)
         print(fake_stats)
         assert_eq_stats(genuine_stats, fake_stats)
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 def test_watchers(started_cluster):
+    try:
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
         genuine_zk.create("/test_data_watches")
@@ -196,8 +203,12 @@ def test_watchers(started_cluster):
         print("Genuine children", genuine_children)
         print("Fake children", fake_children)
         assert genuine_children == fake_children
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 def test_multitransactions(started_cluster):
+    try:
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
         for zk in [genuine_zk, fake_zk]:
@@ -225,7 +236,9 @@ def test_multitransactions(started_cluster):
             assert zk.exists('/test_multitransactions/q') is None
             assert zk.exists('/test_multitransactions/a') is None
             assert zk.exists('/test_multitransactions/x') is None
-
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 def exists(zk, path):
     result = zk.exists(path)
@@ -278,13 +291,13 @@ class Request(object):
         arg_str = ', '.join([str(k) + "=" + str(v) for k, v in self.arguments.items()])
         return "ZKRequest name {} with arguments {}".format(self.name, arg_str)
 
-def generate_requests(iters=1):
+def generate_requests(prefix="/", iters=1):
     requests = []
     existing_paths = []
     for i in range(iters):
         for _ in range(100):
             rand_length = random.randint(0, 10)
-            path = "/"
+            path = prefix
             for j in range(1, rand_length):
                 path = create_random_path(path, 1)
                 existing_paths.append(path)
@@ -322,9 +335,13 @@ def generate_requests(iters=1):
 
 
 def test_random_requests(started_cluster):
-    requests = generate_requests(10)
+    try:
+        requests = generate_requests("/test_random_requests", 10)
+        print("Generated", len(requests), "requests")
         genuine_zk = get_genuine_zk()
         fake_zk = get_fake_zk()
+        genuine_zk.create("/test_random_requests")
+        fake_zk.create("/test_random_requests")
         for i, request in enumerate(requests):
             genuine_throw = False
             fake_throw = False
@@ -333,20 +350,28 @@ def test_random_requests(started_cluster):
             try:
                 genuine_result = request.callback(genuine_zk)
             except Exception as ex:
+                print("i", i, "request", request)
+                print("Genuine exception", str(ex))
                 genuine_throw = True
 
             try:
                 fake_result = request.callback(fake_zk)
             except Exception as ex:
+                print("i", i, "request", request)
+                print("Fake exception", str(ex))
                 fake_throw = True
 
-        assert fake_throw == genuine_throw, "Fake throw genuine not or vise versa"
+            assert fake_throw == genuine_throw, "Fake throw genuine not or vise versa request {}"
             assert fake_result == genuine_result, "Zookeeper results differ"
-    root_children_genuine = [elem for elem in list(sorted(genuine_zk.get_children("/"))) if elem not in ('clickhouse', 'zookeeper')]
-    root_children_fake = [elem for elem in list(sorted(fake_zk.get_children("/"))) if elem not in ('clickhouse', 'zookeeper')]
+        root_children_genuine = [elem for elem in list(sorted(genuine_zk.get_children("/test_random_requests"))) if elem not in ('clickhouse', 'zookeeper')]
+        root_children_fake = [elem for elem in list(sorted(fake_zk.get_children("/test_random_requests"))) if elem not in ('clickhouse', 'zookeeper')]
         assert root_children_fake == root_children_genuine
+    finally:
+        for zk in [genuine_zk, fake_zk]:
+            stop_zk(zk)
 
 def test_end_of_session(started_cluster):
+
     fake_zk1 = None
     fake_zk2 = None
     genuine_zk1 = None
@@ -401,13 +426,8 @@ def test_end_of_session(started_cluster):
         assert fake_ephemeral_event == genuine_ephemeral_event
 
     finally:
-        try:
         for zk in [fake_zk1, fake_zk2, genuine_zk1, genuine_zk2]:
-                if zk:
-                    zk.stop()
-                    zk.close()
-        except:
-            pass
+            stop_zk(zk)
 
 def test_end_of_watches_session(started_cluster):
     fake_zk1 = None
@@ -442,15 +462,11 @@ def test_end_of_watches_session(started_cluster):
 
         assert dummy_set == 2
     finally:
-        try:
         for zk in [fake_zk1, fake_zk2]:
-                if zk:
-                    zk.stop()
-                    zk.close()
-        except:
-            pass
+            stop_zk(zk)
 
 def test_concurrent_watches(started_cluster):
+    try:
         fake_zk = get_fake_zk()
         fake_zk.restart()
         global_path = "/test_concurrent_watches_0"
@@ -530,3 +546,5 @@ def test_concurrent_watches(started_cluster):
             print("Diff", list(set(all_paths_created) - set(all_paths_triggered)))
 
         assert dumb_watch_triggered_counter == watches_must_be_triggered
+    finally:
+        stop_zk(fake_zk)

tests/integration/test_testkeeper_multinode_blocade_leader/configs/enable_test_keeper1.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_blocade_leader/configs/enable_test_keeper2.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>2</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_blocade_leader/configs/enable_test_keeper3.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>3</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_blocade_leader/test.py

@@ -6,6 +6,7 @@ import os
 import time
 from multiprocessing.dummy import Pool
 from helpers.network import PartitionManager
+from helpers.test_tools import assert_eq_with_retry
 
 cluster = ClickHouseCluster(__file__)
 node1 = cluster.add_instance('node1', main_configs=['configs/enable_test_keeper1.xml', 'configs/log_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
@@ -14,6 +15,18 @@ node3 = cluster.add_instance('node3', main_configs=['configs/enable_test_keeper3
 
 from kazoo.client import KazooClient, KazooState
 
+"""
+In this test, we blockade RAFT leader and check that the whole system is
+able to recover. It's not a good test because we use ClickHouse's replicated
+tables to check connectivity, but they may require special operations (or a long
+wait) after session expiration. We don't use kazoo, because this client pretends
+to be very smart: SUSPEND sessions, try to recover them, and so on. The test
+will be even less predictable than with ClickHouse tables.
+
+TODO find (or write) not so smart python client.
+TODO remove this when jepsen tests will be written.
+"""
+
 @pytest.fixture(scope="module")
 def started_cluster():
     try:
@@ -55,7 +68,6 @@ def get_fake_zk(nodename, timeout=30.0):
     _fake_zk_instance = KazooClient(hosts=cluster.get_instance_ip(nodename) + ":9181", timeout=timeout)
     def reset_listener(state):
         nonlocal _fake_zk_instance
-        print("Fake zk callback called for state", state)
         if state != KazooState.CONNECTED:
             _fake_zk_instance._reset()
 
@@ -67,19 +79,25 @@ def get_fake_zk(nodename, timeout=30.0):
 # in extremely rare case it can take more than 5 minutes in debug build with sanitizer
 @pytest.mark.timeout(600)
 def test_blocade_leader(started_cluster):
+    for i in range(100):
         wait_nodes()
+        try:
             for i, node in enumerate([node1, node2, node3]):
                 node.query("CREATE DATABASE IF NOT EXISTS ordinary ENGINE=Ordinary")
-        node.query("CREATE TABLE ordinary.t1 (value UInt64) ENGINE = ReplicatedMergeTree('/clickhouse/t1', '{}') ORDER BY tuple()".format(i + 1))
+                node.query("CREATE TABLE IF NOT EXISTS ordinary.t1 (value UInt64) ENGINE = ReplicatedMergeTree('/clickhouse/t1', '{}') ORDER BY tuple()".format(i + 1))
+            break
+        except Exception as ex:
+            print("Got exception from node", smaller_exception(ex))
+            time.sleep(0.1)
 
     node2.query("INSERT INTO ordinary.t1 SELECT number FROM numbers(10)")
 
     node1.query("SYSTEM SYNC REPLICA ordinary.t1", timeout=10)
     node3.query("SYSTEM SYNC REPLICA ordinary.t1", timeout=10)
 
-    assert node1.query("SELECT COUNT() FROM ordinary.t1") == "10\n"
-    assert node2.query("SELECT COUNT() FROM ordinary.t1") == "10\n"
-    assert node3.query("SELECT COUNT() FROM ordinary.t1") == "10\n"
+    assert_eq_with_retry(node1, "SELECT COUNT() FROM ordinary.t1", "10")
+    assert_eq_with_retry(node2, "SELECT COUNT() FROM ordinary.t1", "10")
+    assert_eq_with_retry(node3, "SELECT COUNT() FROM ordinary.t1", "10")
 
     with PartitionManager() as pm:
         pm.partition_instances(node2, node1)
@@ -87,7 +105,7 @@ def test_blocade_leader(started_cluster):
 
         for i in range(100):
             try:
-                node2.query("SYSTEM RESTART REPLICA ordinary.t1")
+                restart_replica_for_sure(node2, "ordinary.t1", "/clickhouse/t1/replicas/2")
                 node2.query("INSERT INTO ordinary.t1 SELECT rand() FROM numbers(100)")
                 break
             except Exception as ex:
@@ -104,7 +122,7 @@ def test_blocade_leader(started_cluster):
 
         for i in range(100):
             try:
-                node3.query("SYSTEM RESTART REPLICA ordinary.t1")
+                restart_replica_for_sure(node3, "ordinary.t1", "/clickhouse/t1/replicas/3")
                 node3.query("INSERT INTO ordinary.t1 SELECT rand() FROM numbers(100)")
                 break
             except Exception as ex:
@@ -122,7 +140,7 @@ def test_blocade_leader(started_cluster):
     for n, node in enumerate([node1, node2, node3]):
         for i in range(100):
             try:
-                node.query("SYSTEM RESTART REPLICA ordinary.t1")
+                restart_replica_for_sure(node, "ordinary.t1", "/clickhouse/t1/replicas/{}".format(n + 1))
                 break
             except Exception as ex:
                 try:
@@ -150,7 +168,7 @@ def test_blocade_leader(started_cluster):
     for n, node in enumerate([node1, node2, node3]):
         for i in range(100):
             try:
-                node.query("SYSTEM RESTART REPLICA ordinary.t1")
+                restart_replica_for_sure(node, "ordinary.t1", "/clickhouse/t1/replicas/{}".format(n + 1))
                 node.query("SYSTEM SYNC REPLICA ordinary.t1", timeout=10)
                 break
             except Exception as ex:
@@ -170,9 +188,9 @@ def test_blocade_leader(started_cluster):
         for num, node in enumerate([node1, node2, node3]):
             dump_zk(node, '/clickhouse/t1', '/clickhouse/t1/replicas/{}'.format(num + 1))
 
-    assert node1.query("SELECT COUNT() FROM ordinary.t1") == "310\n"
-    assert node2.query("SELECT COUNT() FROM ordinary.t1") == "310\n"
-    assert node3.query("SELECT COUNT() FROM ordinary.t1") == "310\n"
+    assert_eq_with_retry(node1, "SELECT COUNT() FROM ordinary.t1", "310")
+    assert_eq_with_retry(node2, "SELECT COUNT() FROM ordinary.t1", "310")
+    assert_eq_with_retry(node3, "SELECT COUNT() FROM ordinary.t1", "310")
 
 
 def dump_zk(node, zk_path, replica_path):
@@ -188,22 +206,47 @@ def dump_zk(node, zk_path, replica_path):
     print("Parts")
     print(node.query("SELECT name FROM system.zookeeper WHERE path = '{}/parts' FORMAT Vertical".format(replica_path)))
 
+def restart_replica_for_sure(node, table_name, zk_replica_path):
+    fake_zk = None
+    try:
+        node.query("DETACH TABLE {}".format(table_name))
+        fake_zk = get_fake_zk(node.name)
+        if fake_zk.exists(zk_replica_path + "/is_active") is not None:
+            fake_zk.delete(zk_replica_path + "/is_active")
+
+        node.query("ATTACH TABLE {}".format(table_name))
+    except Exception as ex:
+        print("Exception", ex)
+        raise ex
+    finally:
+        if fake_zk:
+            fake_zk.stop()
+            fake_zk.close()
+
+
+
 # in extremely rare case it can take more than 5 minutes in debug build with sanitizer
 @pytest.mark.timeout(600)
 def test_blocade_leader_twice(started_cluster):
+    for i in range(100):
         wait_nodes()
+        try:
             for i, node in enumerate([node1, node2, node3]):
                 node.query("CREATE DATABASE IF NOT EXISTS ordinary ENGINE=Ordinary")
-        node.query("CREATE TABLE ordinary.t2 (value UInt64) ENGINE = ReplicatedMergeTree('/clickhouse/t2', '{}') ORDER BY tuple()".format(i + 1))
+                node.query("CREATE TABLE IF NOT EXISTS ordinary.t2 (value UInt64) ENGINE = ReplicatedMergeTree('/clickhouse/t2', '{}') ORDER BY tuple()".format(i + 1))
+            break
+        except Exception as ex:
+            print("Got exception from node", smaller_exception(ex))
+            time.sleep(0.1)
 
     node2.query("INSERT INTO ordinary.t2 SELECT number FROM numbers(10)")
 
     node1.query("SYSTEM SYNC REPLICA ordinary.t2", timeout=10)
     node3.query("SYSTEM SYNC REPLICA ordinary.t2", timeout=10)
 
-    assert node1.query("SELECT COUNT() FROM ordinary.t2") == "10\n"
-    assert node2.query("SELECT COUNT() FROM ordinary.t2") == "10\n"
-    assert node3.query("SELECT COUNT() FROM ordinary.t2") == "10\n"
+    assert_eq_with_retry(node1, "SELECT COUNT() FROM ordinary.t2", "10")
+    assert_eq_with_retry(node2, "SELECT COUNT() FROM ordinary.t2", "10")
+    assert_eq_with_retry(node3, "SELECT COUNT() FROM ordinary.t2", "10")
 
     with PartitionManager() as pm:
         pm.partition_instances(node2, node1)
@@ -211,7 +254,7 @@ def test_blocade_leader_twice(started_cluster):
 
         for i in range(100):
             try:
-                node2.query("SYSTEM RESTART REPLICA ordinary.t2")
+                restart_replica_for_sure(node2, "ordinary.t2", "/clickhouse/t2/replicas/2")
                 node2.query("INSERT INTO ordinary.t2 SELECT rand() FROM numbers(100)")
                 break
             except Exception as ex:
@@ -228,7 +271,8 @@ def test_blocade_leader_twice(started_cluster):
 
         for i in range(100):
             try:
-                node3.query("SYSTEM RESTART REPLICA ordinary.t2")
+                restart_replica_for_sure(node3, "ordinary.t2", "/clickhouse/t2/replicas/3")
+                node3.query("SYSTEM SYNC REPLICA ordinary.t2", timeout=10)
                 node3.query("INSERT INTO ordinary.t2 SELECT rand() FROM numbers(100)")
                 break
             except Exception as ex:
@@ -243,6 +287,10 @@ def test_blocade_leader_twice(started_cluster):
                 dump_zk(node, '/clickhouse/t2', '/clickhouse/t2/replicas/{}'.format(num + 1))
             assert False, "Cannot reconnect for node3"
 
+        node2.query("SYSTEM SYNC REPLICA ordinary.t2", timeout=10)
+
+        assert_eq_with_retry(node2, "SELECT COUNT() FROM ordinary.t2", "210")
+        assert_eq_with_retry(node3, "SELECT COUNT() FROM ordinary.t2", "210")
 
         # Total network partition
         pm.partition_instances(node3, node2)
@@ -261,11 +309,10 @@ def test_blocade_leader_twice(started_cluster):
             except Exception as ex:
                 time.sleep(0.5)
 
-
     for n, node in enumerate([node1, node2, node3]):
         for i in range(100):
             try:
-                node.query("SYSTEM RESTART REPLICA ordinary.t2")
+                restart_replica_for_sure(node, "ordinary.t2", "/clickhouse/t2/replicas/{}".format(n + 1))
                 break
             except Exception as ex:
                 try:
@@ -293,13 +340,15 @@ def test_blocade_leader_twice(started_cluster):
                 dump_zk(node, '/clickhouse/t2', '/clickhouse/t2/replicas/{}'.format(num + 1))
             assert False, "Cannot reconnect for node{}".format(n + 1)
 
-    for n, node in enumerate([node1, node2, node3]):
         for i in range(100):
+            all_done = True
+            for n, node in enumerate([node1, node2, node3]):
                 try:
-                node.query("SYSTEM RESTART REPLICA ordinary.t2")
+                    restart_replica_for_sure(node, "ordinary.t2", "/clickhouse/t2/replicas/{}".format(n + 1))
                     node.query("SYSTEM SYNC REPLICA ordinary.t2", timeout=10)
                     break
                 except Exception as ex:
+                    all_done = False
                     try:
                         node.query("ATTACH TABLE ordinary.t2")
                     except Exception as attach_ex:
@@ -307,15 +356,18 @@ def test_blocade_leader_twice(started_cluster):
 
                     print("Got exception node{}".format(n + 1), smaller_exception(ex))
                     time.sleep(0.5)
+
+            if all_done:
+                break
         else:
             for num, node in enumerate([node1, node2, node3]):
                 dump_zk(node, '/clickhouse/t2', '/clickhouse/t2/replicas/{}'.format(num + 1))
-            assert False, "Cannot reconnect for node{}".format(n + 1)
+            assert False, "Cannot reconnect in i {} retries".format(i)
 
-    assert node1.query("SELECT COUNT() FROM ordinary.t2") == "510\n"
+    assert_eq_with_retry(node1, "SELECT COUNT() FROM ordinary.t2", "510")
     if node2.query("SELECT COUNT() FROM ordinary.t2") != "510\n":
         for num, node in enumerate([node1, node2, node3]):
             dump_zk(node, '/clickhouse/t2', '/clickhouse/t2/replicas/{}'.format(num + 1))
 
-    assert node2.query("SELECT COUNT() FROM ordinary.t2") == "510\n"
-    assert node3.query("SELECT COUNT() FROM ordinary.t2") == "510\n"
+    assert_eq_with_retry(node2, "SELECT COUNT() FROM ordinary.t2", "510")
+    assert_eq_with_retry(node3, "SELECT COUNT() FROM ordinary.t2", "510")

tests/integration/test_testkeeper_multinode_simple/configs/enable_test_keeper1.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_simple/configs/enable_test_keeper2.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>2</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_simple/configs/enable_test_keeper3.xml

@@ -2,6 +2,7 @@
     <test_keeper_server>
         <tcp_port>9181</tcp_port>
         <server_id>3</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
 
         <coordination_settings>
             <operation_timeout_ms>5000</operation_timeout_ms>

tests/integration/test_testkeeper_multinode_simple/test.py

@@ -6,6 +6,7 @@ import os
 import time
 from multiprocessing.dummy import Pool
 from helpers.network import PartitionManager
+from helpers.test_tools import assert_eq_with_retry
 
 cluster = ClickHouseCluster(__file__)
 node1 = cluster.add_instance('node1', main_configs=['configs/enable_test_keeper1.xml', 'configs/log_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
@@ -234,6 +235,6 @@ def test_simple_replicated_table(started_cluster):
     node1.query("SYSTEM SYNC REPLICA t", timeout=10)
     node3.query("SYSTEM SYNC REPLICA t", timeout=10)
 
-    assert node1.query("SELECT COUNT() FROM t") == "10\n"
-    assert node2.query("SELECT COUNT() FROM t") == "10\n"
-    assert node3.query("SELECT COUNT() FROM t") == "10\n"
+    assert_eq_with_retry(node1, "SELECT COUNT() FROM t", "10")
+    assert_eq_with_retry(node2, "SELECT COUNT() FROM t", "10")
+    assert_eq_with_retry(node3, "SELECT COUNT() FROM t", "10")

tests/integration/test_testkeeper_persistent_log/__init__.py

@@ -0,0 +1 @@
+#!/usr/bin/env python3

tests/integration/test_testkeeper_persistent_log/configs/enable_test_keeper.xml

@@ -0,0 +1,21 @@
+<yandex>
+    <test_keeper_server>
+        <tcp_port>9181</tcp_port>
+        <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
+
+        <coordination_settings>
+            <operation_timeout_ms>5000</operation_timeout_ms>
+            <session_timeout_ms>10000</session_timeout_ms>
+            <raft_logs_level>trace</raft_logs_level>
+        </coordination_settings>
+
+        <raft_configuration>
+            <server>
+                <id>1</id>
+                <hostname>localhost</hostname>
+                <port>44444</port>
+            </server>
+        </raft_configuration>
+    </test_keeper_server>
+</yandex>

tests/integration/test_testkeeper_persistent_log/configs/logs_conf.xml

@@ -0,0 +1,12 @@
+<yandex>
+    <shutdown_wait_unfinished>3</shutdown_wait_unfinished>
+    <logger>
+        <level>trace</level>
+        <log>/var/log/clickhouse-server/log.log</log>
+        <errorlog>/var/log/clickhouse-server/log.err.log</errorlog>
+        <size>1000M</size>
+        <count>10</count>
+        <stderr>/var/log/clickhouse-server/stderr.log</stderr>
+        <stdout>/var/log/clickhouse-server/stdout.log</stdout>
+    </logger>
+</yandex>

tests/integration/test_testkeeper_persistent_log/configs/use_test_keeper.xml

@@ -0,0 +1,8 @@
+<yandex>
+    <zookeeper>
+            <node index="1">
+            <host>node</host>
+            <port>9181</port>
+        </node>
+    </zookeeper>
+</yandex>

tests/integration/test_testkeeper_persistent_log/test.py

@@ -0,0 +1,124 @@
+#!/usr/bin/env python3
+import pytest
+from helpers.cluster import ClickHouseCluster
+import random
+import string
+import os
+import time
+from kazoo.client import KazooClient, KazooState
+
+
+cluster = ClickHouseCluster(__file__)
+
+node = cluster.add_instance('node', main_configs=['configs/enable_test_keeper.xml', 'configs/logs_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
+
+
+def random_string(length):
+    return ''.join(random.choices(string.ascii_lowercase + string.digits, k=length))
+
+def create_random_path(prefix="", depth=1):
+    if depth == 0:
+        return prefix
+    return create_random_path(os.path.join(prefix, random_string(3)), depth - 1)
+
+@pytest.fixture(scope="module")
+def started_cluster():
+    try:
+        cluster.start()
+
+        yield cluster
+
+    finally:
+        cluster.shutdown()
+
+def get_connection_zk(nodename, timeout=30.0):
+    _fake_zk_instance = KazooClient(hosts=cluster.get_instance_ip(nodename) + ":9181", timeout=timeout)
+    def reset_listener(state):
+        nonlocal _fake_zk_instance
+        print("Fake zk callback called for state", state)
+        if state != KazooState.CONNECTED:
+            _fake_zk_instance._reset()
+
+    _fake_zk_instance.add_listener(reset_listener)
+    _fake_zk_instance.start()
+    return _fake_zk_instance
+
+def test_state_after_restart(started_cluster):
+    try:
+        node_zk = None
+        node_zk2 = None
+        node_zk = get_connection_zk("node")
+
+        node_zk.create("/test_state_after_restart", b"somevalue")
+        strs = []
+        for i in range(100):
+            strs.append(random_string(123).encode())
+            node_zk.create("/test_state_after_restart/node" + str(i), strs[i])
+
+        for i in range(100):
+            if i % 7 == 0:
+                node_zk.delete("/test_state_after_restart/node" + str(i))
+
+        node.restart_clickhouse(kill=True)
+
+        node_zk2 = get_connection_zk("node")
+
+        assert node_zk2.get("/test_state_after_restart")[0] == b"somevalue"
+        for i in range(100):
+            if i % 7 == 0:
+                assert node_zk2.exists("/test_state_after_restart/node" + str(i)) is None
+            else:
+                assert len(node_zk2.get("/test_state_after_restart/node" + str(i))[0]) == 123
+                assert node_zk2.get("/test_state_after_restart/node" + str(i))[0] == strs[i]
+    finally:
+        try:
+            if node_zk is not None:
+                node_zk.stop()
+                node_zk.close()
+
+            if node_zk2 is not None:
+                node_zk2.stop()
+                node_zk2.close()
+        except:
+            pass
+
+
+# http://zookeeper-user.578899.n2.nabble.com/Why-are-ephemeral-nodes-written-to-disk-tp7583403p7583418.html
+def test_ephemeral_after_restart(started_cluster):
+    try:
+        node_zk = None
+        node_zk2 = None
+        node_zk = get_connection_zk("node")
+
+        node_zk.create("/test_ephemeral_after_restart", b"somevalue")
+        strs = []
+        for i in range(100):
+            strs.append(random_string(123).encode())
+            node_zk.create("/test_ephemeral_after_restart/node" + str(i), strs[i], ephemeral=True)
+
+        for i in range(100):
+            if i % 7 == 0:
+                node_zk.delete("/test_ephemeral_after_restart/node" + str(i))
+
+        node.restart_clickhouse(kill=True)
+
+        node_zk2 = get_connection_zk("node")
+
+        assert node_zk2.get("/test_ephemeral_after_restart")[0] == b"somevalue"
+        for i in range(100):
+            if i % 7 == 0:
+                assert node_zk2.exists("/test_ephemeral_after_restart/node" + str(i)) is None
+            else:
+                assert len(node_zk2.get("/test_ephemeral_after_restart/node" + str(i))[0]) == 123
+                assert node_zk2.get("/test_ephemeral_after_restart/node" + str(i))[0] == strs[i]
+    finally:
+        try:
+            if node_zk is not None:
+                node_zk.stop()
+                node_zk.close()
+
+            if node_zk2 is not None:
+                node_zk2.stop()
+                node_zk2.close()
+        except:
+            pass

tests/integration/test_testkeeper_persistent_log_multinode/__init__.py

@@ -0,0 +1 @@
+#!/usr/bin/env python3

tests/integration/test_testkeeper_persistent_log_multinode/configs/enable_test_keeper1.xml

@@ -0,0 +1,39 @@
+<yandex>
+    <test_keeper_server>
+        <tcp_port>9181</tcp_port>
+        <server_id>1</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
+
+        <coordination_settings>
+            <operation_timeout_ms>5000</operation_timeout_ms>
+            <session_timeout_ms>10000</session_timeout_ms>
+            <raft_logs_level>trace</raft_logs_level>
+        </coordination_settings>
+
+        <raft_configuration>
+            <server>
+                <id>1</id>
+                <hostname>node1</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <priority>3</priority>
+            </server>
+            <server>
+                <id>2</id>
+                <hostname>node2</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>2</priority>
+            </server>
+            <server>
+                <id>3</id>
+                <hostname>node3</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>1</priority>
+            </server>
+        </raft_configuration>
+    </test_keeper_server>
+</yandex>

tests/integration/test_testkeeper_persistent_log_multinode/configs/enable_test_keeper2.xml

@@ -0,0 +1,39 @@
+<yandex>
+    <test_keeper_server>
+        <tcp_port>9181</tcp_port>
+        <server_id>2</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
+
+        <coordination_settings>
+            <operation_timeout_ms>5000</operation_timeout_ms>
+            <session_timeout_ms>10000</session_timeout_ms>
+            <raft_logs_level>trace</raft_logs_level>
+        </coordination_settings>
+
+        <raft_configuration>
+            <server>
+                <id>1</id>
+                <hostname>node1</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <priority>3</priority>
+            </server>
+            <server>
+                <id>2</id>
+                <hostname>node2</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>2</priority>
+            </server>
+            <server>
+                <id>3</id>
+                <hostname>node3</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>1</priority>
+            </server>
+        </raft_configuration>
+    </test_keeper_server>
+</yandex>

tests/integration/test_testkeeper_persistent_log_multinode/configs/enable_test_keeper3.xml

@@ -0,0 +1,39 @@
+<yandex>
+    <test_keeper_server>
+        <tcp_port>9181</tcp_port>
+        <server_id>3</server_id>
+        <log_storage_path>/var/lib/clickhouse/coordination/log</log_storage_path>
+
+        <coordination_settings>
+            <operation_timeout_ms>5000</operation_timeout_ms>
+            <session_timeout_ms>10000</session_timeout_ms>
+            <raft_logs_level>trace</raft_logs_level>
+        </coordination_settings>
+
+        <raft_configuration>
+            <server>
+                <id>1</id>
+                <hostname>node1</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <priority>3</priority>
+            </server>
+            <server>
+                <id>2</id>
+                <hostname>node2</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>2</priority>
+            </server>
+            <server>
+                <id>3</id>
+                <hostname>node3</hostname>
+                <port>44444</port>
+                <can_become_leader>true</can_become_leader>
+                <start_as_follower>true</start_as_follower>
+                <priority>1</priority>
+            </server>
+        </raft_configuration>
+    </test_keeper_server>
+</yandex>

tests/integration/test_testkeeper_persistent_log_multinode/configs/log_conf.xml

@@ -0,0 +1,12 @@
+<yandex>
+    <shutdown_wait_unfinished>3</shutdown_wait_unfinished>
+    <logger>
+        <level>trace</level>
+        <log>/var/log/clickhouse-server/log.log</log>
+        <errorlog>/var/log/clickhouse-server/log.err.log</errorlog>
+        <size>1000M</size>
+        <count>10</count>
+        <stderr>/var/log/clickhouse-server/stderr.log</stderr>
+        <stdout>/var/log/clickhouse-server/stdout.log</stdout>
+    </logger>
+</yandex>

tests/integration/test_testkeeper_persistent_log_multinode/configs/use_test_keeper.xml

@@ -0,0 +1,16 @@
+<yandex>
+    <zookeeper>
+        <node index="1">
+            <host>node1</host>
+            <port>9181</port>
+        </node>
+        <node index="2">
+            <host>node2</host>
+            <port>9181</port>
+        </node>
+        <node index="3">
+            <host>node3</host>
+            <port>9181</port>
+        </node>
+    </zookeeper>
+</yandex>

tests/integration/test_testkeeper_persistent_log_multinode/test.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+import pytest
+from helpers.cluster import ClickHouseCluster
+import random
+import string
+import os
+import time
+
+cluster = ClickHouseCluster(__file__)
+node1 = cluster.add_instance('node1', main_configs=['configs/enable_test_keeper1.xml', 'configs/log_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
+node2 = cluster.add_instance('node2', main_configs=['configs/enable_test_keeper2.xml', 'configs/log_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
+node3 = cluster.add_instance('node3', main_configs=['configs/enable_test_keeper3.xml', 'configs/log_conf.xml', 'configs/use_test_keeper.xml'], stay_alive=True)
+
+from kazoo.client import KazooClient, KazooState
+
+@pytest.fixture(scope="module")
+def started_cluster():
+    try:
+        cluster.start()
+
+        yield cluster
+
+    finally:
+        cluster.shutdown()
+
+def get_fake_zk(nodename, timeout=30.0):
+    _fake_zk_instance = KazooClient(hosts=cluster.get_instance_ip(nodename) + ":9181", timeout=timeout)
+    def reset_listener(state):
+        nonlocal _fake_zk_instance
+        print("Fake zk callback called for state", state)
+        if state != KazooState.CONNECTED:
+            _fake_zk_instance._reset()
+
+    _fake_zk_instance.add_listener(reset_listener)
+    _fake_zk_instance.start()
+    return _fake_zk_instance
+
+def stop_zk(zk):
+    try:
+        if zk:
+            zk.stop()
+            zk.close()
+    except:
+        pass
+
+def test_restart_multinode(started_cluster):
+    try:
+        node1_zk = node2_zk = node3_zk = None
+
+        node1_zk = get_fake_zk("node1")
+        node2_zk = get_fake_zk("node2")
+        node3_zk = get_fake_zk("node3")
+
+        for i in range(100):
+            node1_zk.create("/test_read_write_multinode_node" + str(i), ("somedata" + str(i)).encode())
+
+        for i in range(100):
+            if i % 10 == 0:
+                node1_zk.delete("/test_read_write_multinode_node" + str(i))
+
+        node2_zk.sync("/test_read_write_multinode_node0")
+        node3_zk.sync("/test_read_write_multinode_node0")
+
+        for i in range(100):
+            if i % 10 != 0:
+                assert node2_zk.get("/test_read_write_multinode_node" + str(i))[0] == ("somedata" + str(i)).encode()
+                assert node3_zk.get("/test_read_write_multinode_node" + str(i))[0] == ("somedata" + str(i)).encode()
+            else:
+                assert node2_zk.exists("/test_read_write_multinode_node" + str(i)) is None
+                assert node3_zk.exists("/test_read_write_multinode_node" + str(i)) is None
+
+    finally:
+        for zk in [node1_zk, node2_zk, node3_zk]:
+            stop_zk(zk)
+
+    node1.restart_clickhouse(kill=True)
+    node2.restart_clickhouse(kill=True)
+    node3.restart_clickhouse(kill=True)
+    for i in range(100):
+        try:
+            node1_zk = get_fake_zk("node1")
+            node2_zk = get_fake_zk("node2")
+            node3_zk = get_fake_zk("node3")
+            for i in range(100):
+                if i % 10 != 0:
+                    assert node1_zk.get("/test_read_write_multinode_node" + str(i))[0] == ("somedata" + str(i)).encode()
+                    assert node2_zk.get("/test_read_write_multinode_node" + str(i))[0] == ("somedata" + str(i)).encode()
+                    assert node3_zk.get("/test_read_write_multinode_node" + str(i))[0] == ("somedata" + str(i)).encode()
+                else:
+                    assert node1_zk.exists("/test_read_write_multinode_node" + str(i)) is None
+                    assert node2_zk.exists("/test_read_write_multinode_node" + str(i)) is None
+                    assert node3_zk.exists("/test_read_write_multinode_node" + str(i)) is None
+            break
+        except Exception as ex:
+            print("Got exception as ex", ex)
+        finally:
+            for zk in [node1_zk, node2_zk, node3_zk]:
+                stop_zk(zk)