org.neo4j.kernel.impl.transaction.log.TransactionLogWriter Maven / Gradle / Ivy

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.transaction.log;

import static org.neo4j.kernel.impl.transaction.log.LogIndexEncoding.encodeLogIndex;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Optional;
import java.util.OptionalLong;
import org.neo4j.kernel.BinarySupportedKernelVersions;
import org.neo4j.kernel.KernelVersion;
import org.neo4j.kernel.KernelVersionProvider;
import org.neo4j.kernel.impl.transaction.CommittedCommandBatchRepresentation;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntryWriter;
import org.neo4j.kernel.impl.transaction.log.rotation.LogRotation;
import org.neo4j.storageengine.api.CommandBatch;
import org.neo4j.util.VisibleForTesting;

public class TransactionLogWriter {
    private final FlushableLogPositionAwareChannel channel;
    private final LogEntryWriter writer;
    private final KernelVersionProvider versionProvider;

    private KernelVersion previousKernelVersion;
    private final LogRotation logRotation;
    private final LogPositionMarker logPositionMarker = new LogPositionMarker();

    public TransactionLogWriter(
            FlushableLogPositionAwareChannel channel,
            KernelVersionProvider versionProvider,
            BinarySupportedKernelVersions binarySupportedKernelVersions,
            LogRotation logRotation) {
        this(channel, new LogEntryWriter<>(channel, binarySupportedKernelVersions), versionProvider, logRotation);
    }

    @VisibleForTesting
    public TransactionLogWriter(
            FlushableLogPositionAwareChannel channel,
            LogEntryWriter writer,
            KernelVersionProvider versionProvider,
            LogRotation logRotation) {
        this.channel = channel;
        this.writer = writer;
        this.versionProvider = versionProvider;
        this.previousKernelVersion = versionProvider.kernelVersion();
        this.logRotation = logRotation;
    }

    public LogPosition beforeAppendPosition() {
        return logPositionMarker.newPosition();
    }

    /*
    * It's possible to append two types of transactions: complete or chunked.
    * Complete transactions are transactions that come with all desired changes in one command batch.
    * This kind of transaction is stored in logs as a sequence of commands like:
    *   start entry -> transactional content -> commit entry
    * Chunked transactions are stored in logs in different chunks where each chunk contains only part of the transaction.
    * This kind of transaction is stored in logs as a sequence of commands like:
        start entry -> chunk start > chunk content -> chunk end -> chunk start > chunk content -> chunk end -> commit entry
    * 
    * An important difference is chunk start/chunk end command pairs. They present only in chunked transactions.
    * The first chunk of chunked transactions comes also with a start entry.
    * The last chunk in the chunked transaction comes with a commit entry at the end.
    */
    public int append(
            CommandBatch batch,
            long transactionId,
            long chunkId,
            long appendIndex,
            int previousChecksum,
            long previousBatchAppendIndex,
            LogAppendEvent logAppendEvent)
            throws IOException {
        KernelVersion kernelVersion = batch.kernelVersion();
        if (kernelVersion == null) {
            kernelVersion = versionProvider.kernelVersion();
        }

        if (kernelVersion != previousKernelVersion) {
            assert kernelVersion.isGreaterThan(previousKernelVersion);
            // The transaction appenders handle locking of the logFile to guarantee only one thread is appending at a
            // time.
            // That means we know we are the only ones using the logfile here, and don't need to lock
            logRotation.locklessRotateLogFile(logAppendEvent, kernelVersion, appendIndex - 1, previousChecksum);
            previousKernelVersion = kernelVersion;
        }
        channel.getCurrentLogPosition(logPositionMarker);

        if (batch.isRollback()) {
            return writer.writeRollbackEntry(kernelVersion, transactionId, appendIndex, batch.getTimeCommitted());
        }

        if (batch.isFirst()) {
            writer.writeStartEntry(
                    kernelVersion,
                    batch.getTimeStarted(),
                    batch.getLatestCommittedTxWhenStarted(),
                    appendIndex,
                    previousChecksum,
                    encodeLogIndex(batch.consensusIndex()));
        } else {
            writer.writeChunkStartEntry(
                    kernelVersion, batch.getTimeCommitted(), chunkId, appendIndex, previousBatchAppendIndex);
        }

        // Write all the commands to the log channel
        writer.serialize(batch, kernelVersion);

        if (batch.isLast()) {
            return writer.writeCommitEntry(kernelVersion, transactionId, batch.getTimeCommitted());
        } else {
            return writer.writeChunkEndEntry(kernelVersion, transactionId, chunkId);
        }
    }

    public int append(CommittedCommandBatchRepresentation commandBatch) throws IOException {
        return commandBatch.serialize(writer);
    }

    public LogPosition getCurrentPosition() throws IOException {
        return channel.getCurrentLogPosition();
    }

    public void resetAppendedBytesCounter() {
        channel.resetAppendedBytesCounter();
    }

    public long getAppendedBytes() {
        return channel.getAppendedBytes();
    }

    public LogPositionMarker getCurrentPosition(LogPositionMarker logPositionMarker) throws IOException {
        return channel.getCurrentLogPosition(logPositionMarker);
    }

    @VisibleForTesting
    public FlushableLogPositionAwareChannel getChannel() {
        return channel;
    }

    public int append(
            ByteBuffer byteBuffer,
            LogAppendEvent logAppendEvent,
            OptionalLong appendIndex,
            Optional kernelVersionByte,
            int checksum,
            long offset)
            throws IOException {
        if (appendIndex.isPresent()) { // append index must be present on a kernel version change.
            KernelVersion kernelVersion = kernelVersionByte
                    .map(KernelVersion::getForVersion /* This one throws if non-recognized kernel version */)
                    .orElse(previousKernelVersion);
            // In append we know we are the only ones using the logfile, don't need to lock on rotation here
            if (kernelVersion != previousKernelVersion) {
                logRotation.locklessRotateLogFile(logAppendEvent, kernelVersion, appendIndex.getAsLong() - 1, checksum);
                previousKernelVersion = kernelVersion;
            } else {
                logRotation.locklessBatchedRotateLogIfNeeded(
                        logAppendEvent, appendIndex.getAsLong() - 1, kernelVersion, checksum);
            }
        }

        channel.getCurrentLogPosition(logPositionMarker);
        return channel.write(byteBuffer, offset);
    }

    @VisibleForTesting
    public LogEntryWriter getWriter() {
        return writer;
    }
}