kafka RemoteLogMetadataSnapshotFile 源码

  • 2022-10-20
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kafka RemoteLogMetadataSnapshotFile 代码


 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *    http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package org.apache.kafka.server.log.remote.metadata.storage;

import org.apache.kafka.common.KafkaException;
import org.apache.kafka.common.utils.Utils;
import org.apache.kafka.server.log.remote.metadata.storage.serialization.RemoteLogMetadataSerde;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

 * This class represents the remote log data snapshot stored in a file for a specific topic partition. This is used by
 * {@link TopicBasedRemoteLogMetadataManager} to store the remote log metadata received for a specific partition from
 * remote log metadata topic. This will avoid reading the remote log metadata messages from the topic again when a
 * broker restarts.
public class RemoteLogMetadataSnapshotFile {
    private static final Logger log = LoggerFactory.getLogger(RemoteLogMetadataSnapshotFile.class);

    public static final String COMMITTED_LOG_METADATA_SNAPSHOT_FILE_NAME = "remote_log_snapshot";

    // File format:
    // <header>[<entry>...]
    // header: <version:short><metadata-partition:int><metadata-partition-offset:long><entries-size:int>
    // entry: <entry-length><entry-bytes>

    // header size: 2 (version) + 4 (partition num) + 8 (offset) + 4 (entries size) = 18
    private static final int HEADER_SIZE = 18;

    private final File metadataStoreFile;
    private final RemoteLogMetadataSerde serde = new RemoteLogMetadataSerde();

     * Creates a CommittedLogMetadataSnapshotFile instance backed by a file with the name `remote_log_snapshot` in
     * the given {@code metadataStoreDir}. It creates the file if it does not exist.
     * @param metadataStoreDir directory in which the snapshot file to be created.
    RemoteLogMetadataSnapshotFile(Path metadataStoreDir) {
        this.metadataStoreFile = new File(metadataStoreDir.toFile(), COMMITTED_LOG_METADATA_SNAPSHOT_FILE_NAME);

        // Create an empty file if it does not exist.
        try {
            final boolean fileExists = Files.exists(metadataStoreFile.toPath());
            if (!fileExists) {
            log.info("Remote log metadata snapshot file: [{}], newFileCreated: [{}]", metadataStoreFile, !fileExists);
        } catch (IOException e) {
            throw new KafkaException(e);

     * Writes the given snapshot replacing the earlier snapshot data.
     * @param snapshot Snapshot to be stored.
     * @throws IOException if there4 is any error in writing the given snapshot to the file.
    public synchronized void write(Snapshot snapshot) throws IOException {
        Path newMetadataSnapshotFilePath = new File(metadataStoreFile.getAbsolutePath() + ".tmp").toPath();
        try (FileChannel fileChannel = FileChannel.open(newMetadataSnapshotFilePath,
                                                        StandardOpenOption.CREATE, StandardOpenOption.READ, StandardOpenOption.WRITE)) {

            // header: <version:short><metadata-partition:int><metadata-partition-offset:long>
            ByteBuffer headerBuffer = ByteBuffer.allocate(HEADER_SIZE);

            // Write version

            // Write metadata partition and metadata partition offset

            // Write metadata partition offset

            // Write entries size
            Collection<RemoteLogSegmentMetadataSnapshot> metadataSnapshots = snapshot.remoteLogSegmentMetadataSnapshots();

            // Write header

            // Write each entry
            ByteBuffer lenBuffer = ByteBuffer.allocate(4);
            for (RemoteLogSegmentMetadataSnapshot metadataSnapshot : metadataSnapshots) {
                final byte[] serializedBytes = serde.serialize(metadataSnapshot);
                // entry format: <entry-length><entry-bytes>

                // Write entry length

                // Write entry bytes


        Utils.atomicMoveWithFallback(newMetadataSnapshotFilePath, metadataStoreFile.toPath());

     * @return the Snapshot if it exists.
     * @throws IOException if there is any error in reading the stored snapshot.
    public synchronized Optional<Snapshot> read() throws IOException {

        // Checking for empty files.
        if (metadataStoreFile.length() == 0) {
            return Optional.empty();

        try (ReadableByteChannel channel = Channels.newChannel(new FileInputStream(metadataStoreFile))) {

            // header: <version:short><metadata-partition:int><metadata-partition-offset:long>
            // Read header
            ByteBuffer headerBuffer = ByteBuffer.allocate(HEADER_SIZE);
            short version = headerBuffer.getShort();
            int metadataPartition = headerBuffer.getInt();
            long metadataPartitionOffset = headerBuffer.getLong();
            int metadataSnapshotsSize = headerBuffer.getInt();

            List<RemoteLogSegmentMetadataSnapshot> result = new ArrayList<>(metadataSnapshotsSize);
            ByteBuffer lenBuffer = ByteBuffer.allocate(4);
            int lenBufferReadCt;
            while ((lenBufferReadCt = channel.read(lenBuffer)) > 0) {

                if (lenBufferReadCt != lenBuffer.capacity()) {
                    throw new IOException("Invalid amount of data read for the length of an entry, file may have been corrupted.");

                // entry format: <entry-length><entry-bytes>

                // Read the length of each entry
                final int len = lenBuffer.getInt();

                // Read the entry
                ByteBuffer data = ByteBuffer.allocate(len);
                final int read = channel.read(data);
                if (read != len) {
                    throw new IOException("Invalid amount of data read, file may have been corrupted.");

                // We are always adding RemoteLogSegmentMetadata only as you can see in #write() method.
                // Did not add a specific serde for RemoteLogSegmentMetadata and reusing RemoteLogMetadataSerde
                final RemoteLogSegmentMetadataSnapshot remoteLogSegmentMetadata =
                        (RemoteLogSegmentMetadataSnapshot) serde.deserialize(data.array());

            if (metadataSnapshotsSize != result.size()) {
                throw new IOException("Unexpected entries in the snapshot file. Expected size: " + metadataSnapshotsSize
                                              + ", but found: " + result.size());

            return Optional.of(new Snapshot(version, metadataPartition, metadataPartitionOffset, result));

     * This class represents the collection of remote log metadata for a specific topic partition.
    public static final class Snapshot {
        private static final short CURRENT_VERSION = 0;

        private final short version;
        private final int metadataPartition;
        private final long metadataPartitionOffset;
        private final Collection<RemoteLogSegmentMetadataSnapshot> remoteLogSegmentMetadataSnapshots;

        public Snapshot(int metadataPartition,
                        long metadataPartitionOffset,
                        Collection<RemoteLogSegmentMetadataSnapshot> remoteLogSegmentMetadataSnapshots) {
            this(CURRENT_VERSION, metadataPartition, metadataPartitionOffset, remoteLogSegmentMetadataSnapshots);

        public Snapshot(short version,
                        int metadataPartition,
                        long metadataPartitionOffset,
                        Collection<RemoteLogSegmentMetadataSnapshot> remoteLogSegmentMetadataSnapshots) {
            // We will add multiple version support in future if needed. For now, the only supported version is CURRENT_VERSION viz 0.
            if (version != CURRENT_VERSION) {
                throw new IllegalArgumentException("Unexpected version received: " + version);
            this.version = version;
            this.metadataPartition = metadataPartition;
            this.metadataPartitionOffset = metadataPartitionOffset;
            this.remoteLogSegmentMetadataSnapshots = remoteLogSegmentMetadataSnapshots;

        public short version() {
            return version;

        public int metadataPartition() {
            return metadataPartition;

        public long metadataPartitionOffset() {
            return metadataPartitionOffset;

        public Collection<RemoteLogSegmentMetadataSnapshot> remoteLogSegmentMetadataSnapshots() {
            return remoteLogSegmentMetadataSnapshots;

        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof Snapshot)) return false;
            Snapshot snapshot = (Snapshot) o;
            return version == snapshot.version && metadataPartition == snapshot.metadataPartition
                    && metadataPartitionOffset == snapshot.metadataPartitionOffset
                    && Objects.equals(remoteLogSegmentMetadataSnapshots, snapshot.remoteLogSegmentMetadataSnapshots);

        public int hashCode() {
            return Objects.hash(version, metadataPartition, metadataPartitionOffset, remoteLogSegmentMetadataSnapshots);

        public String toString() {
            return "Snapshot{" +
                    "version=" + version +
                    ", metadataPartition=" + metadataPartition +
                    ", metadataPartitionOffset=" + metadataPartitionOffset +
                    ", remoteLogSegmentMetadataSnapshotsSize" + remoteLogSegmentMetadataSnapshots.size() +


kafka 源码目录


kafka CommittedOffsetsFile 源码

kafka ConsumerManager 源码

kafka ConsumerTask 源码

kafka FileBasedRemoteLogMetadataCache 源码

kafka ProducerManager 源码

kafka RemoteLogLeaderEpochState 源码

kafka RemoteLogMetadataCache 源码

kafka RemoteLogMetadataTopicPartitioner 源码

kafka RemoteLogSegmentMetadataSnapshot 源码

kafka RemotePartitionMetadataEventHandler 源码

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