- /**
- * 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.OutputStream;
- import org.apache.hadoop.io.Writable;
- /**
- * A generic abstract class to support journaling of edits logs into
- * a persistent storage.
- */
- abstract class EditLogOutputStream extends OutputStream {
- // these are statistics counters
- private long numSync; // number of sync(s) to disk
- private long totalTimeSync; // total time to sync
- EditLogOutputStream() throws IOException {
- numSync = totalTimeSync = 0;
- }
- /**
- * Get this stream name.
- *
- * @return name of the stream
- */
- abstract String getName();
- /** {@inheritDoc} */
- abstract public void write(int b) throws IOException;
- /**
- * Write edits log record into the stream.
- * The record is represented by operation name and
- * an array of Writable arguments.
- *
- * @param op operation
- * @param writables array of Writable arguments
- * @throws IOException
- */
- abstract void write(byte op, Writable ... writables) throws IOException;
- /**
- * Create and initialize new edits log storage.
- *
- * @throws IOException
- */
- abstract void create() throws IOException;
- /** {@inheritDoc} */
- abstract public void close() 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 void setReadyToFlush() throws IOException;
- /**
- * Flush and sync all data that is ready to be flush
- * {@link #setReadyToFlush()} into underlying persistent store.
- * @throws IOException
- */
- abstract protected void flushAndSync() throws IOException;
- /**
- * Flush data to persistent store.
- * Collect sync metrics.
- */
- public void flush() throws IOException {
- numSync++;
- long start = FSNamesystem.now();
- flushAndSync();
- long end = FSNamesystem.now();
- totalTimeSync += (end - start);
- }
- /**
- * Return the size of the current edits log.
- * Length is used to check when it is large enough to start a checkpoint.
- */
- abstract long length() throws IOException;
- /**
- * Return total time spent in {@link #flushAndSync()}
- */
- long getTotalSyncTime() {
- return totalTimeSync;
- }
- /**
- * Return number of calls to {@link #flushAndSync()}
- */
- long getNumSync() {
- return numSync;
- }
- }