satishd commented on a change in pull request #11058: URL: https://github.com/apache/kafka/pull/11058#discussion_r711989743
########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogMetadataSnapshotFile.java ########## @@ -0,0 +1,239 @@ +/* + * 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, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * 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.Uuid; +import org.apache.kafka.common.utils.Utils; +import org.apache.kafka.server.log.remote.metadata.storage.serialization.RemoteLogMetadataSerde; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadata; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.io.File; +import java.io.FileInputStream; +import java.io.FileOutputStream; +import java.io.IOException; +import java.nio.ByteBuffer; +import java.nio.channels.Channels; +import java.nio.channels.ReadableByteChannel; +import java.nio.channels.WritableByteChannel; +import java.nio.file.Path; +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"; + + // header: <version:short><topicId:2 longs><metadata-partition:int><metadata-partition-offset:long> + // size: 2 + (8+8) + 4 + 8 = 30 + private static final int HEADER_SIZE = 30; + + private final File metadataStoreFile; + + /** + * 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 { + boolean newFileCreated = metadataStoreFile.createNewFile(); + log.info("Remote log metadata snapshot file: [{}], newFileCreated: [{}]", metadataStoreFile, newFileCreated); + } 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 { + File newMetadataSnapshotFile = new File(metadataStoreFile.getAbsolutePath() + ".new"); + try (WritableByteChannel fileChannel = Channels.newChannel(new FileOutputStream(newMetadataSnapshotFile))) { + + ByteBuffer headerBuffer = ByteBuffer.allocate(HEADER_SIZE); + + // Write version + headerBuffer.putShort(snapshot.version); + + // Write topic-id + headerBuffer.putLong(snapshot.topicId.getMostSignificantBits()); + headerBuffer.putLong(snapshot.topicId.getLeastSignificantBits()); + + // Write metadata partition and metadata partition offset + headerBuffer.putInt(snapshot.metadataPartition); + headerBuffer.putLong(snapshot.metadataPartitionOffset); + headerBuffer.flip(); + + // Write header + fileChannel.write(headerBuffer); + + // Write each entry + ByteBuffer lenBuffer = ByteBuffer.allocate(4); + RemoteLogMetadataSerde serde = new RemoteLogMetadataSerde(); + for (RemoteLogSegmentMetadata remoteLogSegmentMetadata : snapshot.remoteLogMetadatas) { + final byte[] serializedBytes = serde.serialize(remoteLogSegmentMetadata); + // Write length + lenBuffer.putInt(serializedBytes.length); + lenBuffer.flip(); + fileChannel.write(lenBuffer); + lenBuffer.rewind(); + + // Write data + fileChannel.write(ByteBuffer.wrap(serializedBytes)); + } + } + + Utils.atomicMoveWithFallback(newMetadataSnapshotFile.toPath(), metadataStoreFile.toPath()); + } + + /** + * @return the Snapshot if it exists. + * @throws IOException if there is any error in reading the stored snapshot. + */ + @SuppressWarnings("unchecked") + 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))) { + + // Read header + ByteBuffer headerBuffer = ByteBuffer.allocate(HEADER_SIZE); + channel.read(headerBuffer); + headerBuffer.rewind(); + short version = headerBuffer.getShort(); + Uuid topicId = new Uuid(headerBuffer.getLong(), headerBuffer.getLong()); + int metadataPartition = headerBuffer.getInt(); + long metadataPartitionOffset = headerBuffer.getLong(); + + RemoteLogMetadataSerde serde = new RemoteLogMetadataSerde(); + + List<RemoteLogSegmentMetadata> result = new ArrayList<>(); + + ByteBuffer lenBuffer = ByteBuffer.allocate(4); + while (channel.read(lenBuffer) > 0) { + lenBuffer.rewind(); + // Read the length of each entry + final int len = lenBuffer.getInt(); + lenBuffer.rewind(); + + // 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 RemoteLogSegmentMetadata remoteLogSegmentMetadata = (RemoteLogSegmentMetadata) serde.deserialize(data.array()); + result.add(remoteLogSegmentMetadata); + } + + return Optional.of(new Snapshot(version, topicId, 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 Uuid topicId; + private final int metadataPartition; + private final long metadataPartitionOffset; + private final Collection<RemoteLogSegmentMetadata> remoteLogMetadatas; + + public Snapshot(Uuid topicId, + int metadataPartition, + long metadataPartitionOffset, + Collection<RemoteLogSegmentMetadata> remoteLogMetadatas) { + this(CURRENT_VERSION, topicId, metadataPartition, metadataPartitionOffset, remoteLogMetadatas); + } + + public Snapshot(short version, + Uuid topicId, + int metadataPartition, + long metadataPartitionOffset, + Collection<RemoteLogSegmentMetadata> remoteLogMetadatas) { + this.version = version; + this.topicId = topicId; + this.metadataPartition = metadataPartition; + this.metadataPartitionOffset = metadataPartitionOffset; + this.remoteLogMetadatas = remoteLogMetadatas; + } + + public short version() { + return version; + } + + public Uuid topicId() { + return topicId; + } + + public int metadataPartition() { + return metadataPartition; + } + + public long metadataPartitionOffset() { Review comment: This is used to store it in the snapshot file. -- This is an automated message from the Apache Git Service. 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