A single HLog is used by several HRegions simultaneously. - * - *
Each HRegion is identified by a unique long int. HRegions do
+ *
+ * A single HLog is used by several HRegions simultaneously. + * + *
+ * Each HRegion is identified by a unique long int. HRegions do
* not need to declare themselves before using the HLog; they simply include
- * their HRegion-id in the append or
+ * their HRegion-id in the append or
* completeCacheFlush calls.
*
- *
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. + *
+ * 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. * - *
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. - * - *
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'. + *
+ * 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. + * + *
+ * 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. + * + *
+ * 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);
-
+
static final String HLOG_DATFILE = "hlog.dat.";
+
static final Text METACOLUMN = new Text("METACOLUMN:");
+
static final Text METAROW = new Text("METAROW");
FileSystem fs;
+
Path dir;
+
Configuration conf;
- SequenceFile.Writer writer;
- TreeMap 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).
+ *
+ * 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.
*
- * We need to seize a lock on the writer so that writes are atomic.
* @param regionName
* @param tableName
* @param row
@@ -337,136 +378,121 @@ public class HLog implements HConstants {
* @throws IOException
*/
synchronized void append(Text regionName, Text tableName, Text row,
- TreeMap${ROOTDIR}/log_HOST_PORT
+ * @param srcDir Directory of log files to split: e.g.
+ * ${ROOTDIR}/log_HOST_PORT
* @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});
+ Configuration conf) throws IOException {
+ Path logfiles[] = fs.listPaths(new Path[] { srcDir });
LOG.info("splitting " + logfiles.length + " log(s) in " +
srcDir.toString());
HashMapdir 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.
- *
+ * 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
@@ -173,6 +206,7 @@ public class HLog implements HConstants {
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);
@@ -180,115 +214,117 @@ public class HLog implements HConstants {
fs.mkdirs(dir);
rollWriter();
}
-
- synchronized void setSequenceNumber(long newvalue) {
- if (newvalue > logSeqNum) {
- if (LOG.isDebugEnabled()) {
- LOG.debug("changing sequence number from " + logSeqNum + " to " +
- newvalue);
+
+ /**
+ * 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
+ */
+ void setSequenceNumber(long newvalue) {
+ synchronized (sequenceLock) {
+ if (newvalue > logSeqNum) {
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("changing sequence number from " + logSeqNum + " to " +
+ newvalue);
+ }
+ logSeqNum = newvalue;
}
- logSeqNum = newvalue;
}
}
/**
- * Roll the log writer. That is, start writing log messages to a new file.
+ * Roll the log writer. That is, start writing log messages to a new file.
*
- * The 'rollLock' prevents us from entering rollWriter() more than
- * once at a time.
+ * 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.
+ *
+ * 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
*
- * The 'this' lock limits access to the current writer so
- * we don't append multiple items simultaneously.
- *
* @throws IOException
*/
- void rollWriter() throws IOException {
- synchronized(rollLock) {
+ synchronized void rollWriter() throws IOException {
+ boolean locked = false;
+ while (!locked && !closed) {
+ if (cacheFlushLock.tryLock()) {
+ locked = true;
+ break;
+ }
+ try {
+ this.wait(threadWakeFrequency);
+ } catch (InterruptedException e) {
+ }
+ }
+ if (closed) {
+ if (locked) {
+ cacheFlushLock.unlock();
+ }
+ throw new IOException("Cannot roll log; log is closed");
+ }
- // Try to roll the writer to a new file. We may have to
- // wait for a cache-flush to complete. In the process,
- // compute a list of old log files that can be deleted.
+ // If we get here we have locked out both cache flushes and appends
- Vectorstdout or split the specified log files.
+ *
* @param args
* @throws IOException
*/
@@ -490,7 +517,7 @@ public class HLog implements HConstants {
if (args[0].compareTo("--dump") != 0) {
if (args[0].compareTo("--split") == 0) {
dump = false;
-
+
} else {
usage();
System.exit(-1);
@@ -499,7 +526,7 @@ public class HLog implements HConstants {
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)) {
@@ -513,7 +540,7 @@ public class HLog implements HConstants {
try {
HLogKey key = new HLogKey();
HLogEdit val = new HLogEdit();
- while(log.next(key, val)) {
+ while (log.next(key, val)) {
System.out.println(key.toString() + " " + val.toString());
}
} finally {
diff --git a/src/java/org/apache/hadoop/hbase/HRegion.java b/src/java/org/apache/hadoop/hbase/HRegion.java
index 0fbb32f1e17..60e5acfdb0b 100644
--- a/src/java/org/apache/hadoop/hbase/HRegion.java
+++ b/src/java/org/apache/hadoop/hbase/HRegion.java
@@ -210,6 +210,7 @@ public class HRegion implements HConstants {
final int memcacheFlushSize;
final int blockingMemcacheSize;
protected final long threadWakeFrequency;
+ protected final int optionalFlushCount;
private final HLocking lock = new HLocking();
private long desiredMaxFileSize;
private final long maxSequenceId;
@@ -247,6 +248,8 @@ public class HRegion implements HConstants {
this.regionInfo = regionInfo;
this.memcache = new HMemcache();
this.threadWakeFrequency = conf.getLong(THREAD_WAKE_FREQUENCY, 10 * 1000);
+ this.optionalFlushCount =
+ conf.getInt("hbase.hregion.memcache.optionalflushcount", 10);
// Declare the regionName. This is a unique string for the region, used to
// build a unique filename.
@@ -728,11 +731,13 @@ public class HRegion implements HConstants {
void optionallyFlush() throws IOException {
if(this.memcache.getSize() > this.memcacheFlushSize) {
flushcache(false);
- } else if (this.memcache.getSize() > 0 && this.noFlushCount >= 10) {
- LOG.info("Optional flush called " + this.noFlushCount +
- " times when data present without flushing. Forcing one.");
- flushcache(false);
- if (this.memcache.getSize() > 0) {
+ } else if (this.memcache.getSize() > 0) {
+ if (this.noFlushCount >= this.optionalFlushCount) {
+ LOG.info("Optional flush called " + this.noFlushCount +
+ " times when data present without flushing. Forcing one.");
+ flushcache(false);
+
+ } else {
// Only increment if something in the cache.
// Gets zero'd when a flushcache is called.
this.noFlushCount++;
@@ -864,25 +869,31 @@ public class HRegion implements HConstants {
retval.memcacheSnapshot.size());
}
- // A. Flush memcache to all the HStores.
- // Keep running vector of all store files that includes both old and the
- // just-made new flush store file.
- for (HStore hstore: stores.values()) {
- hstore.flushCache(retval.memcacheSnapshot, retval.sequenceId);
+ try {
+ // A. Flush memcache to all the HStores.
+ // Keep running vector of all store files that includes both old and the
+ // just-made new flush store file.
+ for (HStore hstore: stores.values()) {
+ hstore.flushCache(retval.memcacheSnapshot, retval.sequenceId);
+ }
+ } catch (IOException e) {
+ // An exception here means that the snapshot was not persisted.
+ // The hlog needs to be replayed so its content is restored to memcache.
+ // Currently, only a server restart will do this.
+ this.log.abortCacheFlush();
+ throw new DroppedSnapshotException(e.getMessage());
}
+ // If we get to here, the HStores have been written. If we get an
+ // error in completeCacheFlush it will release the lock it is holding
+
// B. Write a FLUSHCACHE-COMPLETE message to the log.
// This tells future readers that the HStores were emitted correctly,
// and that all updates to the log for this regionName that have lower
// log-sequence-ids can be safely ignored.
this.log.completeCacheFlush(this.regionInfo.regionName,
- regionInfo.tableDesc.getName(), logCacheFlushId);
- } catch (IOException e) {
- // An exception here means that the snapshot was not persisted.
- // The hlog needs to be replayed so its content is restored to memcache.
- // Currently, only a server restart will do this.
- this.log.abortCacheFlush();
- throw new DroppedSnapshotException(e.getMessage());
+ regionInfo.tableDesc.getName(), logCacheFlushId);
+
} finally {
// C. Delete the now-irrelevant memcache snapshot; its contents have been
// dumped to disk-based HStores or, if error, clear aborted snapshot.
diff --git a/src/test/org/apache/hadoop/hbase/TestLogRolling.java b/src/test/org/apache/hadoop/hbase/TestLogRolling.java
new file mode 100644
index 00000000000..25a691bc263
--- /dev/null
+++ b/src/test/org/apache/hadoop/hbase/TestLogRolling.java
@@ -0,0 +1,200 @@
+/**
+ * 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.IOException;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.dfs.MiniDFSCluster;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.io.Text;
+
+/**
+ * Test log deletion as logs are rolled.
+ */
+public class TestLogRolling extends HBaseTestCase {
+ private static final Log LOG = LogFactory.getLog(TestLogRolling.class);
+ private MiniDFSCluster dfs;
+ private MiniHBaseCluster cluster;
+ private Path logdir;
+ private String tableName;
+ private byte[] value;
+
+ /**
+ * constructor
+ * @throws Exception
+ */
+ public TestLogRolling() throws Exception {
+ super();
+ try {
+ this.dfs = null;
+ this.cluster = null;
+ this.logdir = null;
+ this.tableName = null;
+ this.value = null;
+
+ // We roll the log after every 256 writes
+ conf.setInt("hbase.regionserver.maxlogentries", 256);
+
+ // For less frequently updated regions flush after every 2 flushes
+ conf.setInt("hbase.hregion.memcache.optionalflushcount", 2);
+
+ // We flush the cache after every 8192 bytes
+ conf.setInt("hbase.hregion.memcache.flush.size", 8192);
+
+ // Make lease timeout longer, lease checks less frequent
+ conf.setInt("hbase.master.lease.period", 10 * 1000);
+ conf.setInt("hbase.master.lease.thread.wakefrequency", 5 * 1000);
+
+ // Increase the amount of time between client retries
+ conf.setLong("hbase.client.pause", 15 * 1000);
+
+ String className = this.getClass().getName();
+ StringBuilder v = new StringBuilder(className);
+ while (v.length() < 1000) {
+ v.append(className);
+ }
+ value = v.toString().getBytes(HConstants.UTF8_ENCODING);
+
+ } catch (Exception e) {
+ LOG.fatal("error in constructor", e);
+ throw e;
+ }
+ }
+
+ /** {@inheritDoc} */
+ @Override
+ public void setUp() throws Exception {
+ try {
+ super.setUp();
+ dfs = new MiniDFSCluster(conf, 2, true, (String[]) null);
+ } catch (Exception e) {
+ LOG.fatal("error during setUp: ", e);
+ throw e;
+ }
+ }
+
+ /** {@inheritDoc} */
+ @Override
+ public void tearDown() throws Exception {
+ try {
+ super.tearDown();
+
+ if (cluster != null) { // shutdown mini HBase cluster
+ cluster.shutdown();
+ }
+
+ if (dfs != null) {
+ FileSystem fs = dfs.getFileSystem();
+ try {
+ dfs.shutdown();
+ } finally {
+ if (fs != null) {
+ fs.close();
+ }
+ }
+ }
+ } catch (Exception e) {
+ LOG.fatal("error in tearDown", e);
+ throw e;
+ }
+ }
+
+ private void startAndWriteData() throws Exception {
+ cluster = new MiniHBaseCluster(conf, 1, dfs);
+ try {
+ Thread.sleep(10 * 1000); // Wait for region server to start
+ } catch (InterruptedException e) {
+ }
+
+ logdir = cluster.regionThreads.get(0).getRegionServer().getLog().dir;
+
+ // When the META table can be opened, the region servers are running
+ @SuppressWarnings("unused")
+ HTable meta = new HTable(conf, HConstants.META_TABLE_NAME);
+
+ // Create the test table and open it
+ HTableDescriptor desc = new HTableDescriptor(tableName);
+ desc.addFamily(new HColumnDescriptor(HConstants.COLUMN_FAMILY.toString()));
+ HBaseAdmin admin = new HBaseAdmin(conf);
+ admin.createTable(desc);
+ HTable table = new HTable(conf, new Text(tableName));
+
+ for (int i = 1; i <= 2048; i++) { // 2048 writes should cause 8 log rolls
+ long lockid =
+ table.startUpdate(new Text("row" + String.format("%1$04d", i)));
+ table.put(lockid, HConstants.COLUMN_FAMILY, value);
+ table.commit(lockid);
+
+ if (i % 256 == 0) {
+ // After every 256 writes sleep to let the log roller run
+
+ try {
+ Thread.sleep(2000);
+ } catch (InterruptedException e) {
+ }
+ }
+ }
+ }
+
+ private int countLogFiles(boolean print) throws IOException {
+ Path[] logfiles = dfs.getFileSystem().listPaths(new Path[] {logdir});
+ if (print) {
+ for (int i = 0; i < logfiles.length; i++) {
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("logfile: " + logfiles[i].toString());
+ }
+ }
+ }
+ if (LOG.isDebugEnabled()) {
+ LOG.debug("number of log files: " + logfiles.length);
+ }
+ return logfiles.length;
+ }
+
+ /**
+ * Tests that logs are deleted
+ *
+ * @throws Exception
+ */
+ public void testLogRolling() throws Exception {
+ tableName = getName();
+ // Force a region split after every 768KB
+ conf.setLong("hbase.hregion.max.filesize", 768L * 1024L);
+ try {
+ startAndWriteData();
+ LOG.info("Finished writing. Sleeping to let cache flusher and log roller run");
+ try {
+ // Wait for log roller and cache flusher to run a few times...
+ Thread.sleep(30L * 1000L);
+ } catch (InterruptedException e) {
+ LOG.info("Sleep interrupted", e);
+ }
+ LOG.info("Wake from sleep");
+ assertTrue(countLogFiles(true) <= 2);
+ } catch (Exception e) {
+ LOG.fatal("unexpected exception", e);
+ throw e;
+ }
+ }
+
+}