HBase多线程建立HTable问题
最近在写wormhole的HBase plugin，需要分别实现hbase reader和hbase writer，在测试的时候会报错如下：
2013-07-08 09:30:02,568 [pool-2-thread-1] org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.processBatchCallback(HConnectionManager.java:1631) WARN client.HConnectionManager$HConnectionImplementation - Failed all from region=t1,,1373246892580.877bb26da1e4aed541915870fa924224., hostname=test89.hadoop, port=60020
java.util.concurrent.ExecutionException: java.io.IOException: Call to test89.hadoop/10.1.77.89:60020 failed on local exception: java.io.InterruptedIOException: Interruped while waiting for IO on channel java.nio.channels.SocketChannel[connected local=/10.1.77.84:51032 remote=test89.hadoop/10.1.77.89:60020]. 59999 millis timeout left.
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.processBatchCallback(HConnectionManager.java:1601)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.processBatch(HConnectionManager.java:1453)
at org.apache.hadoop.hbase.client.HTable.flushCommits(HTable.java:936)
at org.apache.hadoop.hbase.client.HTable.put(HTable.java:783)
at com.dp.nebula.wormhole.plugins.common.HBaseClient.flush(HBaseClient.java:121)
at com.dp.nebula.wormhole.plugins.writer.hbasewriter.HBaseWriter.commit(HBaseWriter.java:112)
at com.dp.nebula.wormhole.engine.core.WriterThread.call(WriterThread.java:52)
at com.dp.nebula.wormhole.engine.core.WriterThread.call(WriterThread.java:1)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.IOException: Call to test89.hadoop/10.1.77.89:60020 failed on local exception: java.io.InterruptedIOException: Interruped while waiting for IO on channel java.nio.channels.SocketChannel[connected local=/10.1.77.84:51032 remote=test89.hadoop/10.1.77.89:60020]. 59999 millis timeout left.
at org.apache.hadoop.hbase.ipc.HBaseClient.wrapException(HBaseClient.java:1030)
at org.apache.hadoop.hbase.ipc.HBaseClient.call(HBaseClient.java:999)
at org.apache.hadoop.hbase.ipc.SecureRpcEngine$Invoker.invoke(SecureRpcEngine.java:104)
at com.sun.proxy.$Proxy5.multi(Unknown Source)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3$1.call(HConnectionManager.java:1430)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3$1.call(HConnectionManager.java:1428)
at org.apache.hadoop.hbase.client.ServerCallable.withoutRetries(ServerCallable.java:215)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3.call(HConnectionManager.java:1437)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3.call(HConnectionManager.java:1425)
... 5 more
Caused by: java.io.InterruptedIOException: Interruped while waiting for IO on channel java.nio.channels.SocketChannel[connected local=/10.1.77.84:51032 remote=test89.hadoop/10.1.77.89:60020]. 59999 millis timeout left.
2013-07-08 09:30:03,579 [pool-2-thread-6] com.dp.nebula.wormhole.engine.core.WriterThread.call(WriterThread.java:56) ERROR core.WriterThread - Exception occurs in writer thread!
com.dp.nebula.wormhole.common.WormholeException: java.io.IOException: org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation@b7c96a9 closed
at com.dp.nebula.wormhole.plugins.writer.hbasewriter.HBaseWriter.commit(HBaseWriter.java:114)
at com.dp.nebula.wormhole.engine.core.WriterThread.call(WriterThread.java:52)
at com.dp.nebula.wormhole.engine.core.WriterThread.call(WriterThread.java:1)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.IOException: org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation@b7c96a9 closed
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.locateRegion(HConnectionManager.java:877)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.locateRegion(HConnectionManager.java:857)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.processBatchCallback(HConnectionManager.java:1568)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.processBatch(HConnectionManager.java:1453)
at org.apache.hadoop.hbase.client.HTable.flushCommits(HTable.java:936)
at org.apache.hadoop.hbase.client.HTable.put(HTable.java:783)
at com.dp.nebula.wormhole.plugins.common.HBaseClient.flush(HBaseClient.java:121)
at com.dp.nebula.wormhole.plugins.writer.hbasewriter.HBaseWriter.commit(HBaseWriter.java:112)
... 7 more
wormhole的reader和writer会分别起一个ThreadPoolExecutor，出错是在writer端的flush阶段，也就是最后一次批量插入操作。由于我的reader是每一个thread一个htable instance没有问题，而writer是共用了一个singleton HBaseClient，然后用ThreadLocal去保证每一个thread拥有一个本地htable对象，有可能有错误，最简单的方法是把writer端不用singleton HBaseClient，问题应该解决，不过没搞清root cause，不爽啊。。。后来看了HTable和HAdmin的源代码才有点线索
public HTable(Configuration conf, final byte [] tableName)
throws IOException {
this.tableName = tableName;
this.cleanupPoolOnClose = this.cleanupConnectionOnClose = true;
if (conf == null) {
this.connection = null;
return;
}
this.connection = HConnectionManager.getConnection(conf);
this.configuration = conf;
int maxThreads = conf.getInt("hbase.htable.threads.max", Integer.MAX_VALUE);
if (maxThreads == 0) {
maxThreads = 1; // is there a better default?
}
long keepAliveTime = conf.getLong("hbase.htable.threads.keepalivetime", 60);
((ThreadPoolExecutor)this.pool).allowCoreThreadTimeOut(true);
this.finishSetup();
}每一个HTable instance都有一个HConnection对象，它负责与Zookeeper和之后的HBase Cluster建立链接（比如cluster中定位region，locations的cache，当region移动后重新校准），它由HConnectionManager来管理
public static HConnection getConnection(Configuration conf)
throws ZooKeeperConnectionException {
HConnectionKey connectionKey = new HConnectionKey(conf);
synchronized (HBASE_INSTANCES) {
HConnectionImplementation connection = HBASE_INSTANCES.get(connectionKey);
if (connection == null) {
connection = new HConnectionImplementation(conf, true);
HBASE_INSTANCES.put(connectionKey, connection);
}
connection.incCount();
return connection;
}
}
HConnectionManager内部有LRU MAP => HBASE_INSTANCES的静态变量作为cache，key为HConnectionKey，包含了username和指定的properties(由传进去的conf提取), value就是HConnection具体实现HConnectionImplementation，由于传入进去的conf都一样，所以都指向同一个HConnectionImplementation，最后会调用connection.incCount()将client reference count加1
public void close() throws IOException {
if (this.closed) {
return;
}
flushCommits();
if (cleanupPoolOnClose) {
this.pool.shutdown();
}
if (cleanupConnectionOnClose) {
if (this.connection != null) {
this.connection.close();
}
}
this.closed = true;
}
HTable close的时候，会先flushCommits，将writerBuffer中的List<Put>一次性通过connection的processBatch方法处理掉，然后进入close connection逻辑，依据也是reference count，先对其减1，当为0或者是过期connection，就会执行close connection并从HBASE_INSTANCES中remove掉。关闭步骤：
1. 关闭HMasterInterface
2. 关闭一串HRegionInterface
3. 关闭zookeeper watcher
HConnectionImplementation connection = HBASE_INSTANCES
.get(connectionKey);
if (connection != null) {
connection.decCount();
if (connection.isZeroReference() || staleConnection) {
HBASE_INSTANCES.remove(connectionKey);
connection.close(stopProxy);
} else if (stopProxy) {
connection.stopProxyOnClose(stopProxy);
}
}else {
LOG.error("Connection not found in the list, can't delete it "+
"(connection key="+connectionKey+"). May be the key was modified?");
}
HBaseAdmin内部也是一样，也是reference了一个HConnection，可以认为和HTable是共享HConnection
分析到这里再联想到之前的报错信息"java.io.IOException: org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation@b7c96a9 closed"，应该是client reference count数的问题，果然在我的HBaseClient代码里面在初始化环节会new一个singleton HBaseClient，里面new一个HBaseAdmin（thread共享），在各个thread启动时候会new 一个threadloca的htable对象
private HTable getHTable() throws IOException {
HTable htable = threadLocalHtable.get();
if (htable == null) {
htable = new HTable(conf, tableName);
htable.setAutoFlush(autoFlush);
htable.setWriteBufferSize(writeBufferSize);
threadLocalHtable.set(htable);
}
return htable;
}但是我的close方法写的有问题，把HBaseAdmin close了很多遍（每个thread close了一次）
public synchronized void close() throws IOException {
HTable table = threadLocalHtable.get();
if (table != null) {
table.close();
table = null;
threadLocalHtable.remove();
}
if (admin != null) {
admin.close();
}
}假设一种场景，有10个writer线程，那么reference count是11 (10个HTable和1个HBaseAdmin)，前5个thread close没问题，第6个thread先close htable，然后发现引用数为0了，它关闭了HConnection，然后再close admin无效，但是其余4个线程这时候有可能在执行flush操作，HConnection既然已经断了，那肯定没办法flush完啊，抛出异常出来
public void flush() throws IOException {
if (getPutBuffer().size() > 0) {
getHTable().put(getPutBuffer());
clearPutBuffer();
}
}
知道了错误原因后，果断在close HBaseAdmin后，把它指向NULL,这样就不会导致重复关闭的问题了
if (admin != null) {
admin.close();
admin = null;
}
这个问题困扰我几天，网上又找不到任何资料，后来还是看了HBase源代码才有新的发现并解决的，看来真碰到问题一定要懂底层代码才行。
本文链接http://blog.csdn.net/lalaguozhe/article/details/9268753，转载请注明