satishd commented on a change in pull request #11058: URL: https://github.com/apache/kafka/pull/11058#discussion_r722958575
########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogMetadataSnapshotFile.java ########## @@ -0,0 +1,253 @@ +/* + * 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.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.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> + // entry: <entry-length><entry-bytes> + + // header size: 2 (version) + 4 (partition num) + 8 (offset) = 14 + private static final int HEADER_SIZE = 14; + + 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 { + 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 { + 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 + headerBuffer.putShort(snapshot.version()); + + // Write metadata partition and metadata partition offset + headerBuffer.putInt(snapshot.metadataPartition()); + + // Write metadata partition offset + headerBuffer.putLong(snapshot.metadataPartitionOffset()); + headerBuffer.flip(); + + // Write header + fileChannel.write(headerBuffer); + + // Write each entry + ByteBuffer lenBuffer = ByteBuffer.allocate(4); + for (RemoteLogSegmentMetadataSnapshot metadataSnapshot : snapshot.remoteLogSegmentMetadataSnapshots()) { + final byte[] serializedBytes = serde.serialize(metadataSnapshot); + // entry format: <entry-length><entry-bytes> + + // Write entry length + lenBuffer.putInt(serializedBytes.length); + lenBuffer.flip(); + fileChannel.write(lenBuffer); + lenBuffer.rewind(); + + // Write entry bytes + fileChannel.write(ByteBuffer.wrap(serializedBytes)); + } + + fileChannel.force(true); + } + + 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) { Review comment: No, it is not needed in that case. -- This is an automated message from the Apache Git Service. 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