Java tutorial
/* * 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.flume.channel.file; import java.io.EOFException; import java.io.File; import java.io.IOException; import java.util.Collection; import java.util.List; import org.apache.commons.collections.MultiMap; import org.apache.commons.collections.map.MultiValueMap; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.google.common.base.Preconditions; import com.google.common.collect.Lists; /** * Processes a set of data logs, replaying said logs into the queue. */ class ReplayHandler { private static final Logger LOG = LoggerFactory.getLogger(ReplayHandler.class); private final FlumeEventQueue queue; private final long lastCheckpoint; /** * This data structure stores takes for which we found a commit in the log * files before we found a commit for the put. This can happen if the channel * is configured for multiple directories. * * Consider the following: * * logdir1, logdir2 * * Put goes to logdir2 Commit of Put goes to logdir2 Take goes to logdir1 * Commit of Take goes to logdir1 * * When replaying we will start with log1 and find the take and commit before * finding the put and commit in logdir2. */ private final List<Long> pendingTakes; ReplayHandler(FlumeEventQueue queue) { this.queue = queue; this.lastCheckpoint = queue.getTimestamp(); pendingTakes = Lists.newArrayList(); } void replayLog(List<File> logs) throws IOException { int total = 0; int count = 0; MultiMap transactionMap = new MultiValueMap(); LOG.info("Starting replay of " + logs); for (File log : logs) { LOG.info("Replaying " + log); LogFile.SequentialReader reader = null; try { reader = new LogFile.SequentialReader(log); reader.skipToLastCheckpointPosition(queue.getTimestamp()); Pair<Integer, TransactionEventRecord> entry; FlumeEventPointer ptr; // for puts the fileId is the fileID of the file they exist in // for takes the fileId and offset are pointers to a put int fileId = reader.getLogFileID(); int readCount = 0; int putCount = 0; int takeCount = 0; int rollbackCount = 0; int commitCount = 0; int skipCount = 0; while ((entry = reader.next()) != null) { int offset = entry.getLeft(); TransactionEventRecord record = entry.getRight(); short type = record.getRecordType(); long trans = record.getTransactionID(); readCount++; if (record.getTimestamp() > lastCheckpoint) { if (type == TransactionEventRecord.Type.PUT.get()) { putCount++; ptr = new FlumeEventPointer(fileId, offset); transactionMap.put(trans, ptr); } else if (type == TransactionEventRecord.Type.TAKE.get()) { takeCount++; Take take = (Take) record; ptr = new FlumeEventPointer(take.getFileID(), take.getOffset()); transactionMap.put(trans, ptr); } else if (type == TransactionEventRecord.Type.ROLLBACK.get()) { rollbackCount++; transactionMap.remove(trans); } else if (type == TransactionEventRecord.Type.COMMIT.get()) { commitCount++; @SuppressWarnings("unchecked") Collection<FlumeEventPointer> pointers = (Collection<FlumeEventPointer>) transactionMap .remove(trans); if (pointers != null && pointers.size() > 0) { processCommit(((Commit) record).getType(), pointers); count += pointers.size(); } } else { Preconditions.checkArgument(false, "Unknown record type: " + Integer.toHexString(type)); } } else { skipCount++; } } LOG.info("Replayed " + count + " from " + log); if (LOG.isDebugEnabled()) { LOG.debug("read: " + readCount + ", put: " + putCount + ", take: " + takeCount + ", rollback: " + rollbackCount + ", commit: " + commitCount + ", skipp: " + skipCount); } } catch (EOFException e) { LOG.warn("Hit EOF on " + log); } finally { total += count; count = 0; if (reader != null) { reader.close(); } } } int pendingTakesSize = pendingTakes.size(); if (pendingTakesSize > 0) { String msg = "Pending takes " + pendingTakesSize + " exist after the end of replay"; if (LOG.isDebugEnabled()) { for (Long pointer : pendingTakes) { LOG.debug("Pending take " + FlumeEventPointer.fromLong(pointer)); } } else { LOG.error(msg + ". Duplicate messages will exist in destination."); } } LOG.info("Replayed " + total); } private void processCommit(short type, Collection<FlumeEventPointer> pointers) { if (type == TransactionEventRecord.Type.PUT.get()) { for (FlumeEventPointer pointer : pointers) { Preconditions.checkState(queue.addTail(pointer), "Unable to add " + pointer); if (pendingTakes.remove(pointer.toLong())) { Preconditions.checkState(queue.remove(pointer), "Take was pending and pointer was successfully added to the" + " queue but could not be removed: " + pointer); } } } else if (type == TransactionEventRecord.Type.TAKE.get()) { for (FlumeEventPointer pointer : pointers) { boolean removed = queue.remove(pointer); if (!removed) { pendingTakes.add(pointer.toLong()); } } } else { Preconditions.checkArgument(false, "Unknown record type: " + Integer.toHexString(type)); } } }