/**
* Copyright 2007 The Apache Software Foundation
*
* 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.hbase;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.SequenceFile.Reader;
/**
* HLog stores all the edits to the HStore.
*
* It performs logfile-rolling, so external callers are not aware that the
* underlying file is being rolled.
*
* <p>
* A single HLog is used by several HRegions simultaneously.
*
* <p>
* Each HRegion is identified by a unique long <code>int</code>. HRegions do
* not need to declare themselves before using the HLog; they simply include
* their HRegion-id in the <code>append</code> or
* <code>completeCacheFlush</code> calls.
*
* <p>
* An HLog consists of multiple on-disk files, which have a chronological order.
* As data is flushed to other (better) on-disk structures, the log becomes
* obsolete. We can destroy all the log messages for a given HRegion-id up to
* the most-recent CACHEFLUSH message from that HRegion.
*
* <p>
* It's only practical to delete entire files. Thus, we delete an entire on-disk
* file F when all of the messages in F have a log-sequence-id that's older
* (smaller) than the most-recent CACHEFLUSH message for every HRegion that has
* a message in F.
*
* <p>
* Synchronized methods can never execute in parallel. However, between the
* start of a cache flush and the completion point, appends are allowed but log
* rolling is not. To prevent log rolling taking place during this period, a
* separate reentrant lock is used.
*
* <p>
* TODO: Vuk Ercegovac also pointed out that keeping HBase HRegion edit logs in
* HDFS is currently flawed. HBase writes edits to logs and to a memcache. The
* 'atomic' write to the log is meant to serve as insurance against abnormal
* RegionServer exit: on startup, the log is rerun to reconstruct an HRegion's
* last wholesome state. But files in HDFS do not 'exist' until they are cleanly
* closed -- something that will not happen if RegionServer exits without
* running its 'close'.
*/
public class HLog implements HConstants {
private static final Log LOG = LogFactory.getLog(HLog.class);
private static final String HLOG_DATFILE = "hlog.dat.";
static final Text METACOLUMN = new Text("METACOLUMN:");
static final Text METAROW = new Text("METAROW");
final FileSystem fs;
final Path dir;
final Configuration conf;
final long threadWakeFrequency;
/*
* Current log file.
*/
SequenceFile.Writer writer;
/*
* Map of all log files but the current one.
*/
final TreeMap<Long, Path> outputfiles = new TreeMap<Long, Path>();
/*
* Map of region to last sequence/edit id.
*/
final Map<Text, Long> lastSeqWritten = new HashMap<Text, Long>();
volatile boolean closed = false;
private final Integer sequenceLock = new Integer(0);
volatile long logSeqNum = 0;
volatile long filenum = 0;
volatile int numEntries = 0;
// This lock prevents starting a log roll during a cache flush.
// synchronized is insufficient because a cache flush spans two method calls.
private final Lock cacheFlushLock = new ReentrantLock();
/**
* Split up a bunch of log files, that are no longer being written to, into
* new files, one per region. Delete the old log files when finished.
*
* @param rootDir Root directory of the HBase instance
* @param srcDir Directory of log files to split: e.g.
* <code>${ROOTDIR}/log_HOST_PORT</code>
* @param fs FileSystem
* @param conf HBaseConfiguration
* @throws IOException
*/
static void splitLog(Path rootDir, Path srcDir, FileSystem fs,
Configuration conf)
throws IOException {
Path logfiles[] = fs.listPaths(new Path[] { srcDir });
LOG.info("splitting " + logfiles.length + " log(s) in " +
srcDir.toString());
Map<Text, SequenceFile.Writer> logWriters =
new HashMap<Text, SequenceFile.Writer>();
try {
for (int i = 0; i < logfiles.length; i++) {
if (LOG.isDebugEnabled()) {
LOG.debug("Splitting " + logfiles[i]);
}
// Check for empty file.
if (fs.getFileStatus(logfiles[i]).getLen() <= 0) {
LOG.warn("Skipping " + logfiles[i].toString() +
" because zero length");
continue;
}
SequenceFile.Reader in =
new SequenceFile.Reader(fs, logfiles[i], conf);
try {
HLogKey key = new HLogKey();
HLogEdit val = new HLogEdit();
while (in.next(key, val)) {
Text regionName = key.getRegionName();
SequenceFile.Writer w = logWriters.get(regionName);
if (w == null) {
Path logfile = new Path(HRegion.getRegionDir(rootDir,
regionName), HREGION_OLDLOGFILE_NAME);
if (LOG.isDebugEnabled()) {
LOG.debug("getting new log file writer for path " + logfile);
}
w = SequenceFile.createWriter(fs, conf, logfile, HLogKey.class,
HLogEdit.class);
logWriters.put(regionName, w);
}
if (LOG.isDebugEnabled()) {
LOG.debug("Edit " + key.toString() + "=" + val.toString());
}
w.append(key, val);
}
} finally {
in.close();
}
}
} finally {
for (SequenceFile.Writer w : logWriters.values()) {
w.close();
}
}
if (fs.exists(srcDir)) {
if (!fs.delete(srcDir)) {
LOG.error("Cannot delete: " + srcDir);
if (!FileUtil.fullyDelete(new File(srcDir.toString()))) {
throw new IOException("Cannot delete: " + srcDir);
}
}
}
LOG.info("log file splitting completed for " + srcDir.toString());
}
/**
* Create an edit log at the given <code>dir</code> location.
*
* You should never have to load an existing log. If there is a log at
* startup, it should have already been processed and deleted by the time the
* HLog object is started up.
*
* @param fs
* @param dir
* @param conf
* @throws IOException
*/
HLog(final FileSystem fs, final Path dir, final Configuration conf)
throws IOException {
this.fs = fs;
this.dir = dir;
this.conf = conf;
this.threadWakeFrequency = conf.getLong(THREAD_WAKE_FREQUENCY, 10 * 1000);
if (fs.exists(dir)) {
throw new IOException("Target HLog directory already exists: " + dir);
}
fs.mkdirs(dir);
rollWriter();
}
/**
* Called by HRegionServer when it opens a new region to ensure that log
* sequence numbers are always greater than the latest sequence number of the
* region being brought on-line.
*
* @param newvalue We'll set log edit/sequence number to this value if it
* is greater than the current value.
*/
void setSequenceNumber(long newvalue) {
synchronized (sequenceLock) {
if (newvalue > logSeqNum) {
if (LOG.isDebugEnabled()) {
LOG.debug("changing sequence number from " + logSeqNum + " to " +
newvalue);
}
logSeqNum = newvalue;
}
}
}
/**
* Roll the log writer. That is, start writing log messages to a new file.
*
* Because a log cannot be rolled during a cache flush, and a cache flush
* spans two method calls, a special lock needs to be obtained so that a cache
* flush cannot start when the log is being rolled and the log cannot be
* rolled during a cache flush.
*
* <p>Note that this method cannot be synchronized because it is possible that
* startCacheFlush runs, obtaining the cacheFlushLock, then this method could
* start which would obtain the lock on this but block on obtaining the
* cacheFlushLock and then completeCacheFlush could be called which would wait
* for the lock on this and consequently never release the cacheFlushLock
*
* @throws IOException
*/
synchronized void rollWriter() throws IOException {
boolean locked = false;
while (!locked && !closed) {
if (this.cacheFlushLock.tryLock()) {
locked = true;
break;
}
try {
this.wait(threadWakeFrequency);
} catch (InterruptedException e) {
// continue
}
}
if (closed) {
if (locked) {
this.cacheFlushLock.unlock();
}
throw new IOException("Cannot roll log; log is closed");
}
// If we get here we have locked out both cache flushes and appends
try {
if (this.writer != null) {
// Close the current writer, get a new one.
this.writer.close();
Path p = computeFilename(filenum - 1);
if (LOG.isDebugEnabled()) {
LOG.debug("Closing current log writer " + p.toString() +
" to get a new one");
}
if (filenum > 0) {
synchronized (this.sequenceLock) {
this.outputfiles.put(Long.valueOf(this.logSeqNum - 1), p);
}
}
}
Path newPath = computeFilename(filenum++);
this.writer = SequenceFile.createWriter(this.fs, this.conf, newPath,
HLogKey.class, HLogEdit.class);
LOG.info("new log writer created at " + newPath);
// Can we delete any of the old log files?
if (this.outputfiles.size() > 0) {
if (this.lastSeqWritten.size() <= 0) {
LOG.debug("Last sequence written is empty. Deleting all old hlogs");
// If so, then no new writes have come in since all regions were
// flushed (and removed from the lastSeqWritten map). Means can
// remove all but currently open log file.
for (Map.Entry<Long, Path> e : this.outputfiles.entrySet()) {
deleteLogFile(e.getValue(), e.getKey());
}
this.outputfiles.clear();
} else {
// Get oldest edit/sequence id. If logs are older than this id,
// then safe to remove.
TreeSet<Long> sequenceNumbers =
new TreeSet<Long>(this.lastSeqWritten.values());
long oldestOutstandingSeqNum = sequenceNumbers.first().longValue();
// Get the set of all log files whose final ID is older than the
// oldest pending region operation
sequenceNumbers.clear();
sequenceNumbers.addAll(this.outputfiles.headMap(
Long.valueOf(oldestOutstandingSeqNum)).keySet());
// Now remove old log files (if any)
if (LOG.isDebugEnabled()) {
// Find region associated with oldest key -- helps debugging.
Text oldestRegion = null;
for (Map.Entry<Text, Long> e: this.lastSeqWritten.entrySet()) {
if (e.getValue().longValue() == oldestOutstandingSeqNum) {
oldestRegion = e.getKey();
break;
}
}
LOG.debug("Found " + sequenceNumbers.size() + " logs to remove " +
"using oldest outstanding seqnum of " + oldestOutstandingSeqNum +
" from region " + oldestRegion);
}
if (sequenceNumbers.size() > 0) {
for (Long seq : sequenceNumbers) {
deleteLogFile(this.outputfiles.remove(seq), seq);
}
}
}
}
this.numEntries = 0;
} finally {
this.cacheFlushLock.unlock();
}
}
private void deleteLogFile(final Path p, final Long seqno)
throws IOException {
LOG.info("removing old log file " + p.toString() +
" whose highest sequence/edit id is " + seqno);
this.fs.delete(p);
}
/**
* This is a convenience method that computes a new filename with a given
* file-number.
*/
Path computeFilename(final long fn) {
return new Path(dir,
HLOG_DATFILE + String.format("%1$03d", Long.valueOf(fn)));
}
/**
* Shut down the log and delete the log directory
*
* @throws IOException
*/
synchronized void closeAndDelete() throws IOException {
close();
fs.delete(dir);
}
/**
* Shut down the log.
*
* @throws IOException
*/
synchronized void close() throws IOException {
if (LOG.isDebugEnabled()) {
LOG.debug("closing log writer in " + this.dir.toString());
}
this.writer.close();
this.closed = true;
}
/**
* Append a set of edits to the log. Log edits are keyed by regionName,
* rowname, and log-sequence-id.
*
* Later, if we sort by these keys, we obtain all the relevant edits for a
* given key-range of the HRegion (TODO). Any edits that do not have a
* matching {@link HConstants#COMPLETE_CACHEFLUSH} message can be discarded.
*
* <p>
* Logs cannot be restarted once closed, or once the HLog process dies. Each
* time the HLog starts, it must create a new log. This means that other
* systems should process the log appropriately upon each startup (and prior
* to initializing HLog).
*
* synchronized prevents appends during the completion of a cache flush or for
* the duration of a log roll.
*
* @param regionName
* @param tableName
* @param row
* @param columns
* @param timestamp
* @throws IOException
*/
synchronized void append(Text regionName, Text tableName, Text row,
TreeMap<Text, byte[]> columns, long timestamp)
throws IOException {
if (closed) {
throw new IOException("Cannot append; log is closed");
}
long seqNum[] = obtainSeqNum(columns.size());
// The 'lastSeqWritten' map holds the sequence number of the oldest
// write for each region. When the cache is flushed, the entry for the
// region being flushed is removed if the sequence number of the flush
// is greater than or equal to the value in lastSeqWritten.
if (!this.lastSeqWritten.containsKey(regionName)) {
this.lastSeqWritten.put(regionName, Long.valueOf(seqNum[0]));
}
int counter = 0;
for (Map.Entry<Text, byte[]> es : columns.entrySet()) {
HLogKey logKey =
new HLogKey(regionName, tableName, row, seqNum[counter++]);
HLogEdit logEdit = new HLogEdit(es.getKey(), es.getValue(), timestamp);
this.writer.append(logKey, logEdit);
this.numEntries++;
}
}
/** @return How many items have been added to the log */
int getNumEntries() {
return numEntries;
}
/**
* Obtain a log sequence number.
*/
private long obtainSeqNum() {
long value;
synchronized (sequenceLock) {
value = logSeqNum++;
}
return value;
}
/**
* Obtain a specified number of sequence numbers
*
* @param num number of sequence numbers to obtain
* @return array of sequence numbers
*/
private long[] obtainSeqNum(int num) {
long[] results = new long[num];
synchronized (this.sequenceLock) {
for (int i = 0; i < num; i++) {
results[i] = this.logSeqNum++;
}
}
return results;
}
/**
* By acquiring a log sequence ID, we can allow log messages to continue while
* we flush the cache.
*
* Acquire a lock so that we do not roll the log between the start and
* completion of a cache-flush. Otherwise the log-seq-id for the flush will
* not appear in the correct logfile.
*
* @return sequence ID to pass {@link #completeCacheFlush(Text, Text, long)}
* @see #completeCacheFlush(Text, Text, long)
* @see #abortCacheFlush()
*/
long startCacheFlush() {
this.cacheFlushLock.lock();
return obtainSeqNum();
}
/**
* Complete the cache flush
*
* Protected by this and cacheFlushLock
*
* @param regionName
* @param tableName
* @param logSeqId
* @throws IOException
*/
synchronized void completeCacheFlush(final Text regionName,
final Text tableName, final long logSeqId)
throws IOException {
try {
if (this.closed) {
return;
}
this.writer.append(new HLogKey(regionName, tableName, HLog.METAROW, logSeqId),
new HLogEdit(HLog.METACOLUMN, HGlobals.completeCacheFlush.get(),
System.currentTimeMillis()));
this.numEntries++;
Long seq = this.lastSeqWritten.get(regionName);
if (seq != null && logSeqId >= seq.longValue()) {
this.lastSeqWritten.remove(regionName);
}
} finally {
this.cacheFlushLock.unlock();
notifyAll(); // wake up the log roller if it is waiting
}
}
/**
* Abort a cache flush. This method will clear waits on
* {@link #insideCacheFlush}. Call if the flush fails. Note that the only
* recovery for an aborted flush currently is a restart of the regionserver so
* the snapshot content dropped by the failure gets restored to the memcache.
*/
synchronized void abortCacheFlush() {
this.cacheFlushLock.unlock();
notifyAll();
}
private static void usage() {
System.err.println("Usage: java org.apache.hbase.HLog" +
" {--dump <logfile>... | --split <logdir>...}");
}
/**
* Pass one or more log file names and it will either dump out a text version
* on <code>stdout</code> or split the specified log files.
*
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
if (args.length < 2) {
usage();
System.exit(-1);
}
boolean dump = true;
if (args[0].compareTo("--dump") != 0) {
if (args[0].compareTo("--split") == 0) {
dump = false;
} else {
usage();
System.exit(-1);
}
}
Configuration conf = new HBaseConfiguration();
FileSystem fs = FileSystem.get(conf);
Path baseDir = new Path(conf.get(HBASE_DIR, DEFAULT_HBASE_DIR));
for (int i = 1; i < args.length; i++) {
Path logPath = new Path(args[i]);
if (!fs.exists(logPath)) {
throw new FileNotFoundException(args[i] + " does not exist");
}
if (dump) {
if (!fs.isFile(logPath)) {
throw new IOException(args[i] + " is not a file");
}
Reader log = new SequenceFile.Reader(fs, logPath, conf);
try {
HLogKey key = new HLogKey();
HLogEdit val = new HLogEdit();
while (log.next(key, val)) {
System.out.println(key.toString() + " " + val.toString());
}
} finally {
log.close();
}
} else {
if (!fs.getFileStatus(logPath).isDir()) {
throw new IOException(args[i] + " is not a directory");
}
splitLog(baseDir, logPath, fs, conf);
}
}
}
}