Some compileable code

This commit is contained in:
alesapin 2021-03-01 16:33:34 +03:00
parent 91bc4478d7
commit 03960b1eed
9 changed files with 313 additions and 155 deletions

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@ -4,6 +4,11 @@ namespace Coordination
{
void write(uint8_t x, WriteBuffer & out)
{
writeBinary(x, out);
}
void write(size_t x, WriteBuffer & out)
{
x = __builtin_bswap64(x);
@ -64,6 +69,11 @@ void write(const Error & x, WriteBuffer & out)
write(static_cast<int32_t>(x), out);
}
void read(uint8_t & x, ReadBuffer & in)
{
readBinary(x, in);
}
void read(size_t & x, ReadBuffer & in)
{
readBinary(x, in);

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@ -13,9 +13,11 @@ namespace Coordination
using namespace DB;
void write(uint8_t x, WriteBuffer & out);
void write(size_t x, WriteBuffer & out);
void write(int64_t x, WriteBuffer & out);
void write(int32_t x, WriteBuffer & out);
void write(OpNum x, WriteBuffer & out);
void write(bool x, WriteBuffer & out);
void write(const std::string & s, WriteBuffer & out);
@ -38,6 +40,7 @@ void write(const std::vector<T> & arr, WriteBuffer & out)
write(elem, out);
}
void read(uint8_t & x, ReadBuffer & in);
void read(size_t & x, ReadBuffer & in);
void read(int64_t & x, ReadBuffer & in);
void read(int32_t & x, ReadBuffer & in);

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@ -25,7 +25,7 @@ NuKeeperServer::NuKeeperServer(
ResponsesQueue & responses_queue_)
: server_id(server_id_)
, coordination_settings(coordination_settings_)
, state_machine(nuraft::cs_new<NuKeeperStateMachine>(responses_queue_, coordination_settings))
, state_machine(nuraft::cs_new<NuKeeperStateMachine>(responses_queue_, config.getString("test_keeper_server.snapshot_storage_path"), coordination_settings))
, state_manager(nuraft::cs_new<NuKeeperStateManager>(server_id, "test_keeper_server", config, coordination_settings))
, responses_queue(responses_queue_)
{

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@ -29,14 +29,21 @@ NuKeeperStorage::RequestForSession parseRequest(nuraft::buffer & data)
return request_for_session;
}
NuKeeperStateMachine::NuKeeperStateMachine(ResponsesQueue & responses_queue_, const CoordinationSettingsPtr & coordination_settings_)
NuKeeperStateMachine::NuKeeperStateMachine(ResponsesQueue & responses_queue_, const std::string & snapshots_path_, const CoordinationSettingsPtr & coordination_settings_)
: coordination_settings(coordination_settings_)
, storage(coordination_settings->dead_session_check_period_ms.totalMilliseconds())
, snapshot_manager(snapshots_path_)
, responses_queue(responses_queue_)
, last_committed_idx(0)
, log(&Poco::Logger::get("NuKeeperStateMachine"))
{
LOG_DEBUG(log, "Created nukeeper state machine");
}
void NuKeeperStateMachine::init()
{
LOG_DEBUG(log, "Trying to load state machine");
last_committed_idx = snapshot_manager.restoreFromLatestSnapshot(&storage);
LOG_DEBUG(log, "Loaded snapshot with last commited log index {}", last_committed_idx);
}
nuraft::ptr<nuraft::buffer> NuKeeperStateMachine::commit(const size_t log_idx, nuraft::buffer & data)
@ -76,16 +83,12 @@ nuraft::ptr<nuraft::buffer> NuKeeperStateMachine::commit(const size_t log_idx, n
bool NuKeeperStateMachine::apply_snapshot(nuraft::snapshot & s)
{
LOG_DEBUG(log, "Applying snapshot {}", s.get_last_log_idx());
StorageSnapshotPtr snapshot;
{
std::lock_guard<std::mutex> lock(snapshots_lock);
auto entry = snapshots.find(s.get_last_log_idx());
if (entry == snapshots.end())
return false;
snapshot = entry->second;
}
if (s.get_last_log_idx() != latest_snapshot_meta->get_last_log_idx())
throw Exception(ErrorCodes::LOGICAL_ERROR, "Required to apply snapshot with last log index {}, but our last log index is {}",
s.get_last_log_idx(), latest_snapshot_meta->get_last_log_idx());
std::lock_guard lock(storage_lock);
storage = snapshot->storage;
snapshot_manager.deserializeSnapshotFromBuffer(&storage, latest_snapshot_buf);
last_committed_idx = s.get_last_log_idx();
return true;
}
@ -94,41 +97,7 @@ nuraft::ptr<nuraft::snapshot> NuKeeperStateMachine::last_snapshot()
{
// Just return the latest snapshot.
std::lock_guard<std::mutex> lock(snapshots_lock);
auto entry = snapshots.rbegin();
if (entry == snapshots.rend())
return nullptr;
return entry->second->snapshot;
}
NuKeeperStateMachine::StorageSnapshotPtr NuKeeperStateMachine::createSnapshotInternal(nuraft::snapshot & s)
{
nuraft::ptr<nuraft::buffer> snp_buf = s.serialize();
nuraft::ptr<nuraft::snapshot> ss = nuraft::snapshot::deserialize(*snp_buf);
std::lock_guard lock(storage_lock);
return std::make_shared<NuKeeperStateMachine::StorageSnapshot>(ss, storage);
}
NuKeeperStateMachine::StorageSnapshotPtr NuKeeperStateMachine::readSnapshot(nuraft::snapshot & s, nuraft::buffer & in)
{
nuraft::ptr<nuraft::buffer> snp_buf = s.serialize();
nuraft::ptr<nuraft::snapshot> ss = nuraft::snapshot::deserialize(*snp_buf);
NuKeeperStorageSerializer serializer;
ReadBufferFromNuraftBuffer reader(in);
NuKeeperStorage new_storage(coordination_settings->dead_session_check_period_ms.totalMilliseconds());
serializer.deserialize(new_storage, reader);
return std::make_shared<StorageSnapshot>(ss, new_storage);
}
void NuKeeperStateMachine::writeSnapshot(const NuKeeperStateMachine::StorageSnapshotPtr & snapshot, nuraft::ptr<nuraft::buffer> & out)
{
NuKeeperStorageSerializer serializer;
WriteBufferFromNuraftBuffer writer;
serializer.serialize(snapshot->storage, writer);
out = writer.getBuffer();
return latest_snapshot_meta;
}
void NuKeeperStateMachine::create_snapshot(
@ -136,26 +105,12 @@ void NuKeeperStateMachine::create_snapshot(
nuraft::async_result<bool>::handler_type & when_done)
{
LOG_DEBUG(log, "Creating snapshot {}", s.get_last_log_idx());
auto snapshot = createSnapshotInternal(s);
{
std::lock_guard<std::mutex> lock(snapshots_lock);
snapshots[s.get_last_log_idx()] = snapshot;
size_t num = snapshots.size();
if (num > coordination_settings->max_stored_snapshots)
{
auto entry = snapshots.begin();
std::lock_guard lock(storage_lock);
NuKeeperStorageSnapshot snapshot(&storage, s.get_last_log_idx());
latest_snapshot_buf = snapshot_manager.serializeSnapshotToBuffer(snapshot);
auto result_path = snapshot_manager.serializeSnapshotBufferToDisk(*latest_snapshot_buf, s.get_last_log_idx());
LOG_DEBUG(log, "Created snapshot {} with path {}", s.get_last_log_idx(), result_path);
for (size_t i = 0; i < num - coordination_settings->max_stored_snapshots; ++i)
{
if (entry == snapshots.end())
break;
entry = snapshots.erase(entry);
}
}
}
LOG_DEBUG(log, "Created snapshot {}", s.get_last_log_idx());
nuraft::ptr<std::exception> except(nullptr);
bool ret = true;
when_done(ret, except);
@ -170,20 +125,24 @@ void NuKeeperStateMachine::save_logical_snp_obj(
{
LOG_DEBUG(log, "Saving snapshot {} obj_id {}", s.get_last_log_idx(), obj_id);
// Object ID == 0: it contains dummy value, create snapshot context.
if (obj_id == 0)
{
auto new_snapshot = createSnapshotInternal(s);
std::lock_guard<std::mutex> lock(snapshots_lock);
snapshots.try_emplace(s.get_last_log_idx(), std::move(new_snapshot));
std::lock_guard lock(storage_lock);
NuKeeperStorageSnapshot snapshot(&storage, s.get_last_log_idx());
latest_snapshot_buf = snapshot_manager.serializeSnapshotToBuffer(snapshot);
}
else
{
auto received_snapshot = readSnapshot(s, data);
std::lock_guard<std::mutex> lock(snapshots_lock);
snapshots[s.get_last_log_idx()] = std::move(received_snapshot);
latest_snapshot_buf = nuraft::buffer::clone(data);
}
nuraft::ptr<nuraft::buffer> snp_buf = s.serialize();
latest_snapshot_meta = nuraft::snapshot::deserialize(*snp_buf);
auto result_path = snapshot_manager.serializeSnapshotBufferToDisk(*latest_snapshot_buf, s.get_last_log_idx());
LOG_DEBUG(log, "Created snapshot {} with path {}", s.get_last_log_idx(), result_path);
obj_id++;
}
@ -196,29 +155,19 @@ int NuKeeperStateMachine::read_logical_snp_obj(
{
LOG_DEBUG(log, "Reading snapshot {} obj_id {}", s.get_last_log_idx(), obj_id);
StorageSnapshotPtr required_snapshot;
{
std::lock_guard<std::mutex> lock(snapshots_lock);
auto entry = snapshots.find(s.get_last_log_idx());
if (entry == snapshots.end())
{
// Snapshot doesn't exist.
data_out = nullptr;
is_last_obj = true;
return 0;
}
required_snapshot = entry->second;
}
if (obj_id == 0)
{
auto new_snapshot = createSnapshotInternal(s);
writeSnapshot(new_snapshot, data_out);
data_out = nuraft::buffer::alloc(sizeof(int32_t));
nuraft::buffer_serializer bs(data_out);
bs.put_i32(0);
is_last_obj = false;
}
else
{
writeSnapshot(required_snapshot, data_out);
if (s.get_last_log_idx() != latest_snapshot_meta->get_last_log_idx())
throw Exception(ErrorCodes::LOGICAL_ERROR, "Required to apply snapshot with last log index {}, but our last log index is {}",
s.get_last_log_idx(), latest_snapshot_meta->get_last_log_idx());
data_out = nuraft::buffer::clone(*latest_snapshot_buf);
is_last_obj = true;
}
return 0;

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@ -5,6 +5,7 @@
#include <common/logger_useful.h>
#include <Coordination/ThreadSafeQueue.h>
#include <Coordination/CoordinationSettings.h>
#include <Coordination/NuKeeperStorageSerializer.h>
namespace DB
{
@ -14,7 +15,9 @@ using ResponsesQueue = ThreadSafeQueue<NuKeeperStorage::ResponseForSession>;
class NuKeeperStateMachine : public nuraft::state_machine
{
public:
NuKeeperStateMachine(ResponsesQueue & responses_queue_, const CoordinationSettingsPtr & coordination_settings_);
NuKeeperStateMachine(ResponsesQueue & responses_queue_, const std::string & snapshots_path_, const CoordinationSettingsPtr & coordination_settings_);
void init();
nuraft::ptr<nuraft::buffer> pre_commit(const size_t /*log_idx*/, nuraft::buffer & /*data*/) override { return nullptr; }
@ -58,29 +61,16 @@ public:
void shutdownStorage();
private:
struct StorageSnapshot
{
StorageSnapshot(const nuraft::ptr<nuraft::snapshot> & s, const NuKeeperStorage & storage_)
: snapshot(s)
, storage(storage_)
{}
nuraft::ptr<nuraft::snapshot> snapshot;
NuKeeperStorage storage;
};
using StorageSnapshotPtr = std::shared_ptr<StorageSnapshot>;
StorageSnapshotPtr createSnapshotInternal(nuraft::snapshot & s);
StorageSnapshotPtr readSnapshot(nuraft::snapshot & s, nuraft::buffer & in);
static void writeSnapshot(const StorageSnapshotPtr & snapshot, nuraft::ptr<nuraft::buffer> & out);
nuraft::ptr<nuraft::snapshot> latest_snapshot_meta;
nuraft::ptr<nuraft::buffer> latest_snapshot_buf;
CoordinationSettingsPtr coordination_settings;
NuKeeperStorage storage;
NuKeeperSnapshotManager snapshot_manager;
ResponsesQueue & responses_queue;
/// Mutex for snapshots
std::mutex snapshots_lock;
@ -88,9 +78,6 @@ private:
/// Lock for storage
std::mutex storage_lock;
/// Fake snapshot storage
std::map<uint64_t, StorageSnapshotPtr> snapshots;
/// Last committed Raft log number.
std::atomic<size_t> last_committed_idx;
Poco::Logger * log;

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@ -18,6 +18,9 @@ struct NuKeeperStorageRequest;
using NuKeeperStorageRequestPtr = std::shared_ptr<NuKeeperStorageRequest>;
using ResponseCallback = std::function<void(const Coordination::ZooKeeperResponsePtr &)>;
using ChildrenSet = std::unordered_set<std::string>;
using SessionAndTimeout = std::unordered_map<int64_t, int64_t>;
struct NuKeeperStorageSnapshot;
class NuKeeperStorage
{
@ -54,7 +57,6 @@ public:
using Container = SnapshotableHashTable<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, int64_t>;
using SessionIDs = std::vector<int64_t>;
using Watches = std::map<String /* path, relative of root_path */, SessionIDs>;
@ -89,6 +91,12 @@ public:
return result;
}
void addSessionID(int64_t session_id, int64_t session_timeout_ms)
{
session_and_timeout.emplace(session_id, session_timeout_ms);
session_expiry_queue.update(session_id, session_timeout_ms);
}
ResponsesForSessions processRequest(const Coordination::ZooKeeperRequestPtr & request, int64_t session_id, std::optional<int64_t> new_last_zxid);
void finalize();

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@ -1,13 +1,48 @@
#include <Coordination/NuKeeperStorageSerializer.h>
#include <IO/WriteHelpers.h>
#include <Compression/CompressedReadBuffer.h>
#include <Compression/CompressedWriteBuffer.h>
#include <IO/ReadHelpers.h>
#include <Common/ZooKeeper/ZooKeeperIO.h>
#include <Coordination/ReadBufferFromNuraftBuffer.h>
#include <Coordination/WriteBufferFromNuraftBuffer.h>
#include <IO/WriteBufferFromFile.h>
#include <IO/ReadBufferFromFile.h>
#include <IO/copyData.h>
#include <filesystem>
namespace DB
{
namespace ErrorCodes
{
extern const int UNKNOWN_FORMAT_VERSION;
}
namespace
{
size_t getSnapshotPathUpToLogIdx(const String & snapshot_path)
{
std::filesystem::path path(snapshot_path);
std::string filename = path.stem();
Strings name_parts;
splitInto<'_'>(name_parts, filename);
return parse<size_t>(name_parts[1]);
}
std::string getSnapshotFileName(size_t up_to_log_idx)
{
return std::string{"snapshot_"} + std::to_string(up_to_log_idx) + ".bin";
}
String parentPath(const String & path)
{
auto rslash_pos = path.rfind('/');
if (rslash_pos > 0)
return path.substr(0, rslash_pos);
return "/";
}
void writeNode(const NuKeeperStorage::Node & node, WriteBuffer & out)
{
Coordination::write(node.data, out);
@ -29,62 +64,163 @@ namespace
}
}
void NuKeeperStorageSerializer::serialize(const NuKeeperStorage & storage, WriteBuffer & out)
void NuKeeperStorageSnapshot::serialize(const NuKeeperStorageSnapshot & snapshot, WriteBuffer & out)
{
Coordination::write(storage.zxid, out);
Coordination::write(storage.session_id_counter, out);
Coordination::write(storage.container.size(), out);
//for (const auto & [path, node] : storage.container)
//{
// Coordination::write(path, out);
// writeNode(node, out);
//}
Coordination::write(storage.ephemerals.size(), out);
for (const auto & [session_id, paths] : storage.ephemerals)
Coordination::write(static_cast<uint8_t>(snapshot.version), out);
Coordination::write(snapshot.zxid, out);
Coordination::write(snapshot.session_id, out);
Coordination::write(snapshot.snapshot_container_size, out);
for (auto it = snapshot.begin; it != snapshot.end; ++it)
{
const auto & path = it->key;
const auto & node = it->value;
Coordination::write(path, out);
writeNode(node, out);
}
Coordination::write(snapshot.session_and_timeout.size(), out);
for (const auto & [session_id, timeout] : snapshot.session_and_timeout)
{
Coordination::write(session_id, out);
Coordination::write(paths.size(), out);
for (const auto & path : paths)
Coordination::write(path, out);
Coordination::write(timeout, out);
}
}
void NuKeeperStorageSerializer::deserialize(NuKeeperStorage & storage, ReadBuffer & in)
void NuKeeperStorageSnapshot::deserialize(NuKeeperStorage & storage, ReadBuffer & in)
{
int64_t session_id_counter, zxid;
uint8_t version;
Coordination::read(version, in);
if (static_cast<SnapshotVersion>(version) > SnapshotVersion::V0)
throw Exception(ErrorCodes::UNKNOWN_FORMAT_VERSION, "Unsupported snapshot version {}", version);
int64_t session_id, zxid;
Coordination::read(zxid, in);
Coordination::read(session_id_counter, in);
Coordination::read(session_id, in);
storage.zxid = zxid;
storage.session_id_counter = session_id_counter;
storage.session_id_counter = session_id;
size_t container_size;
Coordination::read(container_size, in);
size_t snapshot_container_size;
Coordination::read(snapshot_container_size, in);
//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);
while (storage.ephemerals.size() < ephemerals_size)
size_t current_size = 0;
while (current_size < snapshot_container_size)
{
int64_t session_id;
size_t ephemerals_for_session;
Coordination::read(session_id, in);
Coordination::read(ephemerals_for_session, in);
while (storage.ephemerals[session_id].size() < ephemerals_for_session)
std::string path;
Coordination::read(path, in);
NuKeeperStorage::Node node;
readNode(node, in);
storage.container.insertOrReplace(path, node);
if (path != "/")
{
std::string ephemeral_path;
Coordination::read(ephemeral_path, in);
storage.ephemerals[session_id].emplace(ephemeral_path);
auto parent_path = parentPath(path);
storage.container.updateValue(parent_path, [&path] (NuKeeperStorage::Node & value) { value.children.insert(path); });
}
if (node.ephemeral_owner != 0)
storage.ephemerals[node.ephemeral_owner].insert(path);
current_size++;
}
size_t active_sessions_size;
Coordination::read(active_sessions_size, in);
size_t current_session_size = 0;
while (current_session_size < active_sessions_size)
{
int64_t active_session_id, timeout;
Coordination::read(active_session_id, in);
Coordination::read(timeout, in);
storage.addSessionID(active_session_id, timeout);
current_session_size++;
}
}
NuKeeperStorageSnapshot::NuKeeperStorageSnapshot(NuKeeperStorage * storage_, size_t up_to_log_idx_)
: storage(storage_)
, up_to_log_idx(up_to_log_idx_)
, zxid(storage->getZXID())
, session_id(storage->session_id_counter)
{
storage->enableSnapshotMode();
snapshot_container_size = storage->container.snapshotSize();
begin = storage->getSnapshotIteratorBegin();
end = storage->getSnapshotIteratorEnd();
session_and_timeout = storage->getActiveSessions();
}
NuKeeperStorageSnapshot::~NuKeeperStorageSnapshot()
{
storage->clearGarbageAfterSnapshot();
storage->disableSnapshotMode();
}
NuKeeperSnapshotManager::NuKeeperSnapshotManager(const std::string & snapshots_path_)
: snapshots_path(snapshots_path_)
{
namespace fs = std::filesystem;
if (!fs::exists(snapshots_path))
fs::create_directories(snapshots_path);
for (const auto & p : fs::directory_iterator(snapshots_path))
{
size_t snapshot_up_to = getSnapshotPathUpToLogIdx(p.path());
existing_snapshots[snapshot_up_to] = p.path();
}
}
std::string NuKeeperSnapshotManager::serializeSnapshotBufferToDisk(nuraft::buffer & buffer, size_t up_to_log_idx)
{
ReadBufferFromNuraftBuffer reader(buffer);
std::string new_snapshot_path = std::filesystem::path{snapshots_path} / getSnapshotFileName(up_to_log_idx);
WriteBufferFromFile plain_buf(new_snapshot_path);
copyData(reader, plain_buf);
plain_buf.sync();
return new_snapshot_path;
}
nuraft::ptr<nuraft::buffer> NuKeeperSnapshotManager::deserializeSnapshotBufferFromDisk(size_t up_to_log_idx) const
{
const std::string & snapshot_path = existing_snapshots.at(up_to_log_idx);
WriteBufferFromNuraftBuffer writer;
ReadBufferFromFile reader(snapshot_path);
copyData(reader, writer);
return writer.getBuffer();
}
nuraft::ptr<nuraft::buffer> NuKeeperSnapshotManager::serializeSnapshotToBuffer(const NuKeeperStorageSnapshot & snapshot)
{
WriteBufferFromNuraftBuffer writer;
CompressedWriteBuffer compressed_writer(writer);
NuKeeperStorageSnapshot::serialize(snapshot, compressed_writer);
return writer.getBuffer();
}
void NuKeeperSnapshotManager::deserializeSnapshotFromBuffer(NuKeeperStorage * storage, nuraft::ptr<nuraft::buffer> buffer)
{
ReadBufferFromNuraftBuffer reader(buffer);
CompressedReadBuffer compressed_reader(reader);
NuKeeperStorageSnapshot::deserialize(*storage, compressed_reader);
}
size_t NuKeeperSnapshotManager::restoreFromLatestSnapshot(NuKeeperStorage * storage) const
{
if (existing_snapshots.empty())
return 0 ;
auto log_id = existing_snapshots.rbegin()->first;
auto buffer = deserializeSnapshotBufferFromDisk(log_id);
deserializeSnapshotFromBuffer(storage, buffer);
return log_id;
}
}

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@ -1,4 +1,5 @@
#pragma once
#include <libnuraft/nuraft.hxx> // Y_IGNORE
#include <Coordination/NuKeeperStorage.h>
#include <IO/WriteBuffer.h>
#include <IO/ReadBuffer.h>
@ -6,12 +7,49 @@
namespace DB
{
class NuKeeperStorageSerializer
enum SnapshotVersion : uint8_t
{
V0 = 0,
};
struct NuKeeperStorageSnapshot
{
public:
static void serialize(const NuKeeperStorage & storage, WriteBuffer & out);
NuKeeperStorageSnapshot(NuKeeperStorage * storage_, size_t up_to_log_idx_);
~NuKeeperStorageSnapshot();
static void serialize(const NuKeeperStorageSnapshot & snapshot, WriteBuffer & out);
static void deserialize(NuKeeperStorage & storage, ReadBuffer & in);
NuKeeperStorage * storage;
SnapshotVersion version = SnapshotVersion::V0;
size_t up_to_log_idx;
int64_t zxid;
int64_t session_id;
size_t snapshot_container_size;
NuKeeperStorage::Container::const_iterator begin;
NuKeeperStorage::Container::const_iterator end;
SessionAndTimeout session_and_timeout;
};
class NuKeeperSnapshotManager
{
public:
explicit NuKeeperSnapshotManager(const std::string & snapshots_path_);
size_t restoreFromLatestSnapshot(NuKeeperStorage * storage) const;
std::string serializeSnapshotBufferToDisk(nuraft::buffer & buffer, size_t up_to_log_idx);
nuraft::ptr<nuraft::buffer> deserializeSnapshotBufferFromDisk(size_t up_to_log_idx) const;
static nuraft::ptr<nuraft::buffer> serializeSnapshotToBuffer(const NuKeeperStorageSnapshot & snapshot);
static void deserializeSnapshotFromBuffer(NuKeeperStorage * storage, nuraft::ptr<nuraft::buffer> buffer);
private:
const std::string snapshots_path;
std::map<size_t, std::string> existing_snapshots;
};
}

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@ -50,6 +50,33 @@ public:
return false;
}
void insertOrReplace(const std::string & key, const V & value)
{
auto it = map.find(key);
if (it == map.end())
{
ListElem elem{key, value, true};
auto itr = list.insert(list.end(), elem);
map.emplace(itr->key, itr);
}
else
{
auto list_itr = it->second;
if (snapshot_mode)
{
ListElem elem{key, value, true};
list_itr->active_in_map = false;
auto new_list_itr = list.insert(list.end(), elem);
map[new_list_itr->key] = new_list_itr;
}
else
{
list_itr->value = value;
}
}
}
bool erase(const std::string & key)
{
auto it = map.find(key);