ClickHouse/dbms/Storages/MergeTree/ReplicatedMergeTreeBlockOutputStream.cpp

#include <Storages/StorageReplicatedMergeTree.h>
#include <Storages/MergeTree/ReplicatedMergeTreeQuorumEntry.h>
#include <Storages/MergeTree/ReplicatedMergeTreeBlockOutputStream.h>
#include <Interpreters/PartLog.h>
#include <DataStreams/IBlockOutputStream.h>
#include <Common/SipHash.h>
#include <Common/ZooKeeper/KeeperException.h>
#include <IO/Operators.h>


namespace ProfileEvents
{
    extern const Event DuplicatedInsertedBlocks;
}

namespace DB
{

namespace ErrorCodes
{
    extern const int TOO_FEW_LIVE_REPLICAS;
    extern const int UNSATISFIED_QUORUM_FOR_PREVIOUS_WRITE;
    extern const int UNEXPECTED_ZOOKEEPER_ERROR;
    extern const int NO_ZOOKEEPER;
    extern const int READONLY;
    extern const int UNKNOWN_STATUS_OF_INSERT;
    extern const int INSERT_WAS_DEDUPLICATED;
    extern const int TIMEOUT_EXCEEDED;
    extern const int NO_ACTIVE_REPLICAS;
}


ReplicatedMergeTreeBlockOutputStream::ReplicatedMergeTreeBlockOutputStream(
    StorageReplicatedMergeTree & storage_, size_t quorum_, size_t quorum_timeout_ms_, size_t max_parts_per_block_, bool deduplicate_)
    : storage(storage_), quorum(quorum_), quorum_timeout_ms(quorum_timeout_ms_), max_parts_per_block(max_parts_per_block_), deduplicate(deduplicate_),
    log(&Logger::get(storage.getLogName() + " (Replicated OutputStream)"))
{
    /// The quorum value `1` has the same meaning as if it is disabled.
    if (quorum == 1)
        quorum = 0;
}


Block ReplicatedMergeTreeBlockOutputStream::getHeader() const
{
    return storage.getSampleBlock();
}


/// Allow to verify that the session in ZooKeeper is still alive.
static void assertSessionIsNotExpired(zkutil::ZooKeeperPtr & zookeeper)
{
    if (!zookeeper)
        throw Exception("No ZooKeeper session.", ErrorCodes::NO_ZOOKEEPER);

    if (zookeeper->expired())
        throw Exception("ZooKeeper session has been expired.", ErrorCodes::NO_ZOOKEEPER);
}


void ReplicatedMergeTreeBlockOutputStream::checkQuorumPrecondition(zkutil::ZooKeeperPtr & zookeeper)
{
    quorum_info.status_path = storage.zookeeper_path + "/quorum/status";

    std::future<Coordination::GetResponse> quorum_status_future = zookeeper->asyncTryGet(quorum_info.status_path);
    std::future<Coordination::GetResponse> is_active_future = zookeeper->asyncTryGet(storage.replica_path + "/is_active");
    std::future<Coordination::GetResponse> host_future = zookeeper->asyncTryGet(storage.replica_path + "/host");

    /// List of live replicas. All of them register an ephemeral node for leader_election.

    Coordination::Stat leader_election_stat;
    zookeeper->get(storage.zookeeper_path + "/leader_election", &leader_election_stat);

    if (leader_election_stat.numChildren < static_cast<int32_t>(quorum))
        throw Exception("Number of alive replicas ("
            + toString(leader_election_stat.numChildren) + ") is less than requested quorum (" + toString(quorum) + ").",
            ErrorCodes::TOO_FEW_LIVE_REPLICAS);

    /** Is there a quorum for the last part for which a quorum is needed?
        * Write of all the parts with the included quorum is linearly ordered.
        * This means that at any time there can be only one part,
        *  for which you need, but not yet reach the quorum.
        * Information about this part will be located in `/quorum/status` node.
        * If the quorum is reached, then the node is deleted.
        */

    auto quorum_status = quorum_status_future.get();
    if (quorum_status.error != Coordination::ZNONODE)
        throw Exception("Quorum for previous write has not been satisfied yet. Status: " + quorum_status.data, ErrorCodes::UNSATISFIED_QUORUM_FOR_PREVIOUS_WRITE);

    /// Both checks are implicitly made also later (otherwise there would be a race condition).

    auto is_active = is_active_future.get();
    auto host = host_future.get();

    if (is_active.error == Coordination::ZNONODE || host.error == Coordination::ZNONODE)
        throw Exception("Replica is not active right now", ErrorCodes::READONLY);

    quorum_info.is_active_node_value = is_active.data;
    quorum_info.is_active_node_version = is_active.stat.version;
    quorum_info.host_node_version = host.stat.version;
}


void ReplicatedMergeTreeBlockOutputStream::write(const Block & block)
{
    last_block_is_duplicate = false;

    /// TODO Is it possible to not lock the table structure here?
    storage.delayInsertOrThrowIfNeeded(&storage.partial_shutdown_event);

    auto zookeeper = storage.getZooKeeper();
    assertSessionIsNotExpired(zookeeper);

    /** If write is with quorum, then we check that the required number of replicas is now live,
      *  and also that for all previous parts for which quorum is required, this quorum is reached.
      * And also check that during the insertion, the replica was not reinitialized or disabled (by the value of `is_active` node).
      * TODO Too complex logic, you can do better.
      */
    if (quorum)
        checkQuorumPrecondition(zookeeper);

    auto part_blocks = storage.writer.splitBlockIntoParts(block, max_parts_per_block);

    for (auto & current_block : part_blocks)
    {
        Stopwatch watch;

        /// Write part to the filesystem under temporary name. Calculate a checksum.

        MergeTreeData::MutableDataPartPtr part = storage.writer.writeTempPart(current_block);

        String block_id;

        if (deduplicate)
        {
            SipHash hash;
            part->checksums.computeTotalChecksumDataOnly(hash);
            union
            {
                char bytes[16];
                UInt64 words[2];
            } hash_value;
            hash.get128(hash_value.bytes);

            /// We add the hash from the data and partition identifier to deduplication ID.
            /// That is, do not insert the same data to the same partition twice.
            block_id = part->info.partition_id + "_" + toString(hash_value.words[0]) + "_" + toString(hash_value.words[1]);

            LOG_DEBUG(log, "Wrote block with ID '" << block_id << "', " << block.rows() << " rows");
        }
        else
        {
            LOG_DEBUG(log, "Wrote block with " << block.rows() << " rows");
        }

        try
        {
            commitPart(zookeeper, part, block_id);

            /// Set a special error code if the block is duplicate
            int error = (deduplicate && last_block_is_duplicate) ? ErrorCodes::INSERT_WAS_DEDUPLICATED : 0;
            PartLog::addNewPart(storage.global_context, part, watch.elapsed(), ExecutionStatus(error));
        }
        catch (...)
        {
            PartLog::addNewPart(storage.global_context, part, watch.elapsed(), ExecutionStatus::fromCurrentException(__PRETTY_FUNCTION__));
            throw;
        }
    }
}


void ReplicatedMergeTreeBlockOutputStream::writeExistingPart(MergeTreeData::MutableDataPartPtr & part)
{
    last_block_is_duplicate = false;

    /// NOTE: No delay in this case. That's Ok.

    auto zookeeper = storage.getZooKeeper();
    assertSessionIsNotExpired(zookeeper);

    if (quorum)
        checkQuorumPrecondition(zookeeper);

    Stopwatch watch;

    try
    {
        commitPart(zookeeper, part, "");
        PartLog::addNewPart(storage.global_context, part, watch.elapsed());
    }
    catch (...)
    {
        PartLog::addNewPart(storage.global_context, part, watch.elapsed(), ExecutionStatus::fromCurrentException(__PRETTY_FUNCTION__));
        throw;
    }
}


void ReplicatedMergeTreeBlockOutputStream::commitPart(zkutil::ZooKeeperPtr & zookeeper, MergeTreeData::MutableDataPartPtr & part, const String & block_id)
{
    storage.check(part->getColumns());
    assertSessionIsNotExpired(zookeeper);

    /// Obtain incremental block number and lock it. The lock holds our intention to add the block to the filesystem.
    /// We remove the lock just after renaming the part. In case of exception, block number will be marked as abandoned.
    /// Also, make deduplication check. If a duplicate is detected, no nodes are created.

    /// Allocate new block number and check for duplicates
    bool deduplicate_block = !block_id.empty();
    String block_id_path = deduplicate_block ? storage.zookeeper_path + "/blocks/" + block_id : "";
    auto block_number_lock = storage.allocateBlockNumber(part->info.partition_id, zookeeper, block_id_path);

    if (!block_number_lock)
    {
        LOG_INFO(log, "Block with ID " << block_id << " already exists; ignoring it.");
        part->is_duplicate = true;
        last_block_is_duplicate = true;
        ProfileEvents::increment(ProfileEvents::DuplicatedInsertedBlocks);
        return;
    }

    Int64 block_number = block_number_lock->getNumber();

    /// Set part attributes according to part_number. Prepare an entry for log.

    part->info.min_block = block_number;
    part->info.max_block = block_number;
    part->info.level = 0;

    String part_name = part->getNewName(part->info);
    part->name = part_name;

    StorageReplicatedMergeTree::LogEntry log_entry;
    log_entry.type = StorageReplicatedMergeTree::LogEntry::GET_PART;
    log_entry.create_time = time(nullptr);
    log_entry.source_replica = storage.replica_name;
    log_entry.new_part_name = part_name;
    log_entry.quorum = quorum;
    log_entry.block_id = block_id;

    /// Simultaneously add information about the part to all the necessary places in ZooKeeper and remove block_number_lock.

    /// Information about the part.
    Coordination::Requests ops;

    storage.getCommitPartOps(ops, part, block_id_path);

    /// Replication log.
    ops.emplace_back(zkutil::makeCreateRequest(
        storage.zookeeper_path + "/log/log-",
        log_entry.toString(),
        zkutil::CreateMode::PersistentSequential));

    /// Deletes the information that the block number is used for writing.
    block_number_lock->getUnlockOps(ops);

    /** If you need a quorum - create a node in which the quorum is monitored.
        * (If such a node already exists, then someone has managed to make another quorum record at the same time, but for it the quorum has not yet been reached.
        *  You can not do the next quorum record at this time.)
        */
    if (quorum)
    {
        ReplicatedMergeTreeQuorumEntry quorum_entry;
        quorum_entry.part_name = part_name;
        quorum_entry.required_number_of_replicas = quorum;
        quorum_entry.replicas.insert(storage.replica_name);

        /** At this point, this node will contain information that the current replica received a part.
            * When other replicas will receive this part (in the usual way, processing the replication log),
            *  they will add themselves to the contents of this node.
            * When it contains information about `quorum` number of replicas, this node is deleted,
            *  which indicates that the quorum has been reached.
            */

        ops.emplace_back(
            zkutil::makeCreateRequest(
                quorum_info.status_path,
                quorum_entry.toString(),
                zkutil::CreateMode::Persistent));

        /// Make sure that during the insertion time, the replica was not reinitialized or disabled (when the server is finished).
        ops.emplace_back(
            zkutil::makeCheckRequest(
                storage.replica_path + "/is_active",
                quorum_info.is_active_node_version));

        /// Unfortunately, just checking the above is not enough, because `is_active` node can be deleted and reappear with the same version.
        /// But then the `host` value will change. We will check this.
        /// It's great that these two nodes change in the same transaction (see MergeTreeRestartingThread).
        ops.emplace_back(
            zkutil::makeCheckRequest(
                storage.replica_path + "/host",
                quorum_info.host_node_version));
    }

    MergeTreeData::Transaction transaction(storage); /// If you can not add a part to ZK, we'll remove it back from the working set.
    storage.renameTempPartAndAdd(part, nullptr, &transaction);

    Coordination::Responses responses;
    int32_t multi_code = zookeeper->tryMultiNoThrow(ops, responses); /// 1 RTT

    if (multi_code == Coordination::ZOK)
    {
        transaction.commit();
        storage.merge_selecting_task->schedule();

        /// Lock nodes have been already deleted, do not delete them in destructor
        block_number_lock->assumeUnlocked();
    }
    else if (multi_code == Coordination::ZCONNECTIONLOSS
        || multi_code == Coordination::ZOPERATIONTIMEOUT)
    {
        /** If the connection is lost, and we do not know if the changes were applied, we can not delete the local part
          *  if the changes were applied, the inserted block appeared in `/blocks/`, and it can not be inserted again.
          */
        transaction.commit();
        storage.enqueuePartForCheck(part->name, MAX_AGE_OF_LOCAL_PART_THAT_WASNT_ADDED_TO_ZOOKEEPER);

        /// We do not know whether or not data has been inserted.
        throw Exception("Unknown status, client must retry. Reason: " + String(Coordination::errorMessage(multi_code)),
            ErrorCodes::UNKNOWN_STATUS_OF_INSERT);
    }
    else if (Coordination::isUserError(multi_code))
    {
        String failed_op_path = zkutil::KeeperMultiException(multi_code, ops, responses).getPathForFirstFailedOp();

        if (multi_code == Coordination::ZNODEEXISTS && deduplicate_block && failed_op_path == block_id_path)
        {
            /// Block with the same id have just appeared in table (or other replica), rollback thee insertion.
            LOG_INFO(log, "Block with ID " << block_id << " already exists; ignoring it (removing part " << part->name << ")");

            part->is_duplicate = true;
            transaction.rollback();
            last_block_is_duplicate = true;
            ProfileEvents::increment(ProfileEvents::DuplicatedInsertedBlocks);
        }
        else if (multi_code == Coordination::ZNODEEXISTS && failed_op_path == quorum_info.status_path)
        {
            transaction.rollback();

            throw Exception("Another quorum insert has been already started", ErrorCodes::UNSATISFIED_QUORUM_FOR_PREVIOUS_WRITE);
        }
        else
        {
            /// NOTE: We could be here if the node with the quorum existed, but was quickly removed.
            transaction.rollback();
            throw Exception("Unexpected logical error while adding block " + toString(block_number) + " with ID '" + block_id + "': "
                            + zkutil::ZooKeeper::error2string(multi_code) + ", path " + failed_op_path,
                            ErrorCodes::UNEXPECTED_ZOOKEEPER_ERROR);
        }
    }
    else if (Coordination::isHardwareError(multi_code))
    {
        transaction.rollback();
        throw Exception("Unrecoverable network error while adding block " + toString(block_number) + " with ID '" + block_id + "': "
                        + zkutil::ZooKeeper::error2string(multi_code), ErrorCodes::UNEXPECTED_ZOOKEEPER_ERROR);
    }
    else
    {
        transaction.rollback();
        throw Exception("Unexpected ZooKeeper error while adding block " + toString(block_number) + " with ID '" + block_id + "': "
                        + zkutil::ZooKeeper::error2string(multi_code), ErrorCodes::UNEXPECTED_ZOOKEEPER_ERROR);
    }

    if (quorum)
    {
        /// We are waiting for quorum to be satisfied.
        LOG_TRACE(log, "Waiting for quorum");

        String quorum_status_path = storage.zookeeper_path + "/quorum/status";

        try
        {
            while (true)
            {
                zkutil::EventPtr event = std::make_shared<Poco::Event>();

                std::string value;
                /// `get` instead of `exists` so that `watch` does not leak if the node is no longer there.
                if (!zookeeper->tryGet(quorum_status_path, value, nullptr, event))
                    break;

                ReplicatedMergeTreeQuorumEntry quorum_entry(value);

                /// If the node has time to disappear, and then appear again for the next insert.
                if (quorum_entry.part_name != part_name)
                    break;

                if (!event->tryWait(quorum_timeout_ms))
                    throw Exception("Timeout while waiting for quorum", ErrorCodes::TIMEOUT_EXCEEDED);
            }

            /// And what if it is possible that the current replica at this time has ceased to be active and the quorum is marked as failed and deleted?
            String value;
            if (!zookeeper->tryGet(storage.replica_path + "/is_active", value, nullptr)
                || value != quorum_info.is_active_node_value)
                throw Exception("Replica become inactive while waiting for quorum", ErrorCodes::NO_ACTIVE_REPLICAS);
        }
        catch (...)
        {
            /// We do not know whether or not data has been inserted
            /// - whether other replicas have time to download the part and mark the quorum as done.
            throw Exception("Unknown status, client must retry. Reason: " + getCurrentExceptionMessage(false),
                ErrorCodes::UNKNOWN_STATUS_OF_INSERT);
        }

        LOG_TRACE(log, "Quorum satisfied");
    }
}

void ReplicatedMergeTreeBlockOutputStream::writePrefix()
{
    storage.throwInsertIfNeeded();
}


}