ClickHouse/dbms/src/Storages/MergeTree/ReplicatedMergeTreeCleanupThread.cpp

#include <Storages/MergeTree/ReplicatedMergeTreeCleanupThread.h>
#include <Storages/StorageReplicatedMergeTree.h>
#include <Common/setThreadName.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int NOT_FOUND_NODE;
}


ReplicatedMergeTreeCleanupThread::ReplicatedMergeTreeCleanupThread(StorageReplicatedMergeTree & storage_)
    : storage(storage_),
    log(&Logger::get(storage.database_name + "." + storage.table_name + " (StorageReplicatedMergeTree, CleanupThread)")),
    thread([this] { run(); }) {}


void ReplicatedMergeTreeCleanupThread::run()
{
    setThreadName("ReplMTCleanup");

    const auto CLEANUP_SLEEP_MS = 30 * 1000;

    while (!storage.shutdown_called)
    {
        try
        {
            iterate();
        }
        catch (...)
        {
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }

        storage.shutdown_event.tryWait(CLEANUP_SLEEP_MS);
    }

    LOG_DEBUG(log, "Cleanup thread finished");
}


void ReplicatedMergeTreeCleanupThread::iterate()
{
    storage.clearOldPartsAndRemoveFromZK(log);
    storage.data.clearOldTemporaryDirectories();

    if (storage.is_leader_node)
    {
        clearOldLogs();
        clearOldBlocks();
    }
}


void ReplicatedMergeTreeCleanupThread::clearOldLogs()
{
    auto zookeeper = storage.getZooKeeper();

    zkutil::Stat stat;
    if (!zookeeper->exists(storage.zookeeper_path + "/log", &stat))
        throw Exception(storage.zookeeper_path + "/log doesn't exist", ErrorCodes::NOT_FOUND_NODE);

    int children_count = stat.numChildren;

    /// We will wait for 1.1 times more records to accumulate than necessary.
    if (static_cast<double>(children_count) < storage.data.settings.replicated_logs_to_keep * 1.1)
        return;

    Strings replicas = zookeeper->getChildren(storage.zookeeper_path + "/replicas", &stat);
    UInt64 min_pointer = std::numeric_limits<UInt64>::max();
    for (const String & replica : replicas)
    {
        String pointer = zookeeper->get(storage.zookeeper_path + "/replicas/" + replica + "/log_pointer");
        if (pointer.empty())
            return;
        min_pointer = std::min(min_pointer, parse<UInt64>(pointer));
    }

    Strings entries = zookeeper->getChildren(storage.zookeeper_path + "/log");
    std::sort(entries.begin(), entries.end());

    /// We will not touch the last `replicated_logs_to_keep` records.
    entries.erase(entries.end() - std::min(entries.size(), storage.data.settings.replicated_logs_to_keep), entries.end());
    /// We will not touch records that are no less than `min_pointer`.
    entries.erase(std::lower_bound(entries.begin(), entries.end(), "log-" + padIndex(min_pointer)), entries.end());

    if (entries.empty())
        return;

    zkutil::Ops ops;
    for (size_t i = 0; i < entries.size(); ++i)
    {
        ops.emplace_back(std::make_unique<zkutil::Op::Remove>(storage.zookeeper_path + "/log/" + entries[i], -1));

        if (ops.size() > 400 || i + 1 == entries.size())
        {
            /// Simultaneously with clearing the log, we check to see if replica was added since we received replicas list.
            ops.emplace_back(std::make_unique<zkutil::Op::Check>(storage.zookeeper_path + "/replicas", stat.version));
            zookeeper->multi(ops);
            ops.clear();
        }
    }

    LOG_DEBUG(log, "Removed " << entries.size() << " old log entries: " << entries.front() << " - " << entries.back());
}


void ReplicatedMergeTreeCleanupThread::clearOldBlocks()
{
    auto zookeeper = storage.getZooKeeper();

    zkutil::Stat stat;
    if (!zookeeper->exists(storage.zookeeper_path + "/blocks", &stat))
        throw Exception(storage.zookeeper_path + "/blocks doesn't exist", ErrorCodes::NOT_FOUND_NODE);

    int children_count = stat.numChildren;

    /// To make "asymptotically" fewer `exists` requests, we will wait for 1.1 times more blocks to accumulate than necessary.
    if (static_cast<double>(children_count) < storage.data.settings.replicated_deduplication_window * 1.1)
        return;

    LOG_TRACE(log, "Clearing about " << static_cast<size_t>(children_count) - storage.data.settings.replicated_deduplication_window
        << " old blocks from ZooKeeper. This might take several minutes.");

    Strings blocks = zookeeper->getChildren(storage.zookeeper_path + "/blocks");

    std::vector<std::pair<Int64, String> > timed_blocks;

    for (const String & block : blocks)
    {
        zkutil::Stat stat;
        zookeeper->exists(storage.zookeeper_path + "/blocks/" + block, &stat);
        timed_blocks.push_back(std::make_pair(stat.czxid, block));
    }

    std::sort(timed_blocks.begin(), timed_blocks.end(), std::greater<std::pair<Int64, String>>());
    for (size_t i = storage.data.settings.replicated_deduplication_window; i < timed_blocks.size(); ++i)
    {
        /// TODO After about half a year, we could replace this to multi op, because there will be no obsolete children nodes.
        zookeeper->removeRecursive(storage.zookeeper_path + "/blocks/" + timed_blocks[i].second);
    }

    LOG_TRACE(log, "Cleared " << blocks.size() - storage.data.settings.replicated_deduplication_window << " old blocks from ZooKeeper");
}

}