| /** |
| * 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.hadoop.hdfs.server.namenode; |
| |
| import java.io.IOException; |
| import java.io.Closeable; |
| |
| import static org.apache.hadoop.util.Time.now; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.jasper.compiler.JspUtil; |
| |
| /** |
| * A generic abstract class to support journaling of edits logs into |
| * a persistent storage. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Evolving |
| public abstract class EditLogOutputStream implements Closeable { |
| // these are statistics counters |
| private long numSync; // number of sync(s) to disk |
| private long totalTimeSync; // total time to sync |
| |
| public EditLogOutputStream() throws IOException { |
| numSync = totalTimeSync = 0; |
| } |
| |
| /** |
| * Write edits log operation to the stream. |
| * |
| * @param op operation |
| * @throws IOException |
| */ |
| abstract public void write(FSEditLogOp op) throws IOException; |
| |
| /** |
| * Write raw data to an edit log. This data should already have |
| * the transaction ID, checksum, etc included. It is for use |
| * within the BackupNode when replicating edits from the |
| * NameNode. |
| * |
| * @param bytes the bytes to write. |
| * @param offset offset in the bytes to write from |
| * @param length number of bytes to write |
| * @throws IOException |
| */ |
| abstract public void writeRaw(byte[] bytes, int offset, int length) |
| throws IOException; |
| |
| /** |
| * Create and initialize underlying persistent edits log storage. |
| * |
| * @throws IOException |
| */ |
| abstract public void create() throws IOException; |
| |
| /** |
| * Close the journal. |
| * @throws IOException if the journal can't be closed, |
| * or if there are unflushed edits |
| */ |
| @Override |
| abstract public void close() throws IOException; |
| |
| /** |
| * Close the stream without necessarily flushing any pending data. |
| * This may be called after a previous write or close threw an exception. |
| */ |
| abstract public void abort() throws IOException; |
| |
| /** |
| * All data that has been written to the stream so far will be flushed. |
| * New data can be still written to the stream while flushing is performed. |
| */ |
| abstract public void setReadyToFlush() throws IOException; |
| |
| /** |
| * Flush and sync all data that is ready to be flush |
| * {@link #setReadyToFlush()} into underlying persistent store. |
| * @param durable if true, the edits should be made truly durable before |
| * returning |
| * @throws IOException |
| */ |
| abstract protected void flushAndSync(boolean durable) throws IOException; |
| |
| /** |
| * Flush data to persistent store. |
| * Collect sync metrics. |
| */ |
| public void flush() throws IOException { |
| flush(true); |
| } |
| |
| public void flush(boolean durable) throws IOException { |
| numSync++; |
| long start = now(); |
| flushAndSync(durable); |
| long end = now(); |
| totalTimeSync += (end - start); |
| } |
| |
| /** |
| * Implement the policy when to automatically sync the buffered edits log |
| * The buffered edits can be flushed when the buffer becomes full or |
| * a certain period of time is elapsed. |
| * |
| * @return true if the buffered data should be automatically synced to disk |
| */ |
| public boolean shouldForceSync() { |
| return false; |
| } |
| |
| /** |
| * Return total time spent in {@link #flushAndSync()} |
| */ |
| long getTotalSyncTime() { |
| return totalTimeSync; |
| } |
| |
| /** |
| * Return number of calls to {@link #flushAndSync()} |
| */ |
| protected long getNumSync() { |
| return numSync; |
| } |
| |
| /** |
| * @return a short HTML snippet suitable for describing the current |
| * status of the stream |
| */ |
| public String generateHtmlReport() { |
| return JspUtil.escapeXml(this.toString()); |
| } |
| } |