HRegionServer的功能
1. HRegionServer主要负责响应用户I/O请求，向底层文件系统中读写数据，是HBase中最核心的模块。
HRegionServer内存管理了一系列的HRegion对象，每个HRegion对应了table中的一个Region.
HRegion由多个HStore组成，每个HStore对应了table中的一个colum family的存储。即就是一个集中的存储单元。
2. HRegionServer实现了4个接口类：HRegionInterface， HBaseRPCErrorHandler，Runnable， RegionServerServices
HRegionInterface：Client通过此接口与HRegionServer进行交互，如获取region的meta信息（getRegionInfo）、get、put、delete等操作。
HBaseRPCErrorHandler：处理RPC调用错误，如OOME(OutOfMemoryError)
Runnable：Runnable是Thread的接口，Runnable只有一个run方法。
RegionServerServices：RegionServer提供的服务接口
3.HRegionServer的入口:
/**
* @see org.apache.hadoop.hbase.regionserver.HRegionServerCommandLine
*/
public static void main(String[] args) throws Exception {
VersionInfo.logVersion();
Configuration conf = HBaseConfiguration.create();
@SuppressWarnings("unchecked")
Class<? extends HRegionServer> regionServerClass = (Class<? extends HRegionServer>) conf
.getClass(HConstants.REGION_SERVER_IMPL, HRegionServer.class);
new HRegionServerCommandLine(regionServerClass).doMain(args);
}
从主函数main，然后调用其相应的CommandLine类HRegionServerCommandLine的doMain方法启动。
4.HRegionServer启动
下面来分析下HRegionServer的启动过程，HRegionServer实现了Runnable接口，所以主要看一下run方法的实现。
(1)startRegionServer方法：
/**
* @param hrs
* @param name
* @return Thread the RegionServer is running in correctly named.
* @throws IOException
*/
public static Thread startRegionServer(final HRegionServer hrs,
final String name) throws IOException {
Thread t = new Thread(hrs);
t.setName(name);
t.start();
// Install shutdown hook that will catch signals and run an orderly shutdown
// of the hrs.
ShutdownHook.install(hrs.getConfiguration(), FileSystem.get(hrs
.getConfiguration()), hrs, t);
return t;
}
(2)run方法：
/**
* The HRegionServer sticks in this loop until closed.
*/
@SuppressWarnings("deprecation")
public void run() {
try {
// Do pre-registration initializations; zookeeper, lease threads, etc.
/*
* initializeZooKeeper()
* 1.初始化ZooKeeper，创建到ZooKeeper的连接
* 2.然后创建MasterAddressManager master的地址管理器，之后阻塞，一直等待master上线。
* 3.master创建之后，创建ClusterStatusTracker对象，等待集群的启动，即等待master将zookeeper设置为up状态。
* 4.最后就是创建CatalogTracker对象，并启动它，从而获取-ROOT-和.META.的地址
*/
preRegistrationInitialization();
} catch (Throwable e) {
abort("Fatal exception during initialization", e);
}
try {
// Try and register with the Master; tell it we are here. Break if
// server is stopped or the clusterup flag is down or hdfs went wacky.
//等待集群up
while (keepLooping()) {
MapWritable w = reportForDuty();
if (w == null) {
LOG.warn("reportForDuty failed; sleeping and then retrying.");
this.sleeper.sleep();
} else {
handleReportForDutyResponse(w);
break;
}
}
registerMBean();
// We registered with the Master. Go into run mode.
long lastMsg = 0;
long oldRequestCount = -1;
// The main run loop.
while (!this.stopped && isHealthy()) {
if (!isClusterUp()) {
if (isOnlineRegionsEmpty()) {
stop("Exiting; cluster shutdown set and not carrying any regions");
} else if (!this.stopping) {
this.stopping = true;
LOG.info("Closing user regions");
closeUserRegions(this.abortRequested);
} else if (this.stopping) {
boolean allUserRegionsOffline = areAllUserRegionsOffline();
if (allUserRegionsOffline) {
// Set stopped if no requests since last time we went around the loop.
// The remaining meta regions will be closed on our way out.
if (oldRequestCount == this.requestCount.get()) {
stop("Stopped; only catalog regions remaining online");
break;
}
oldRequestCount = this.requestCount.get();
} else {
// Make sure all regions have been closed -- some regions may
// have not got it because we were splitting at the time of
// the call to closeUserRegions.
closeUserRegions(this.abortRequested);
}
LOG.debug("Waiting on " + getOnlineRegionsAsPrintableString());
}
}
long now = System.currentTimeMillis();
if ((now - lastMsg) >= msgInterval) {
doMetrics();
tryRegionServerReport();
lastMsg = System.currentTimeMillis();
}
if (!this.stopped) this.sleeper.sleep();
} // for
} catch (Throwable t) {
if (!checkOOME(t)) {
abort("Unhandled exception: " + t.getMessage(), t);
}
}
// Run shutdown.
if (mxBean != null) {
MBeanUtil.unregisterMBean(mxBean);
mxBean = null;
}
this.leases.closeAfterLeasesExpire();
this.rpcServer.stop();
if (this.splitLogWorker != null) {
splitLogWorker.stop();
}
if (this.infoServer != null) {
LOG.info("Stopping infoServer");
try {
this.infoServer.stop();
} catch (Exception e) {
e.printStackTrace();
}
}
// Send cache a shutdown.
if (cacheConfig.isBlockCacheEnabled()) {
cacheConfig.getBlockCache().shutdown();
}
// Send interrupts to wake up threads if sleeping so they notice shutdown.
// TODO: Should we check they are alive? If OOME could have exited already
if (this.cacheFlusher != null) this.cacheFlusher.interruptIfNecessary();
if (this.compactSplitThread != null) this.compactSplitThread.interruptIfNecessary();
if (this.hlogRoller != null) this.hlogRoller.interruptIfNecessary();
if (this.compactionChecker != null)
this.compactionChecker.interrupt();
if (this.killed) {
// Just skip out w/o closing regions. Used when testing.
} else if (abortRequested) {
if (this.fsOk) {
closeAllRegions(abortRequested); // Don't leave any open file handles
}
LOG.info("aborting server " + this.serverNameFromMasterPOV);
} else {
closeAllRegions(abortRequested);
closeAllScanners();
LOG.info("stopping server " + this.serverNameFromMasterPOV);
}
// Interrupt catalog tracker here in case any regions being opened out in
// handlers are stuck waiting on meta or root.
if (this.catalogTracker != null) this.catalogTracker.stop();
if (this.fsOk) {
waitOnAllRegionsToClose(abortRequested);
LOG.info("stopping server " + this.serverNameFromMasterPOV +
"; all regions closed.");
}
//fsOk flag may be changed when closing regions throws exception.
if (!this.killed && this.fsOk) {
closeWAL(abortRequested ? false : true);
}
// Make sure the proxy is down.
if (this.hbaseMaster != null) {
HBaseRPC.stopProxy(this.hbaseMaster);
this.hbaseMaster = null;
}
this.leases.close();
try {
deleteMyEphemeralNode();
} catch (KeeperException e) {
LOG.warn("Failed deleting my ephemeral node", e);
}
this.zooKeeper.close();
LOG.info("stopping server " + this.serverNameFromMasterPOV +
"; zookeeper connection closed.");
if (!killed) {
/*
* 关闭compactionChecker、cacheFlusher、hlogRoller、
* compactSplitThread、service、
*/
join();
}
LOG.info(Thread.currentThread().getName() + " exiting");
}
总结：
HRegionServer启动
1.初始化ZooKeeper，创建到ZooKeeper的连接
2.创建MasterAddressManager master的地址管理器，之后阻塞，一直等待master上线。
3.master创建之后，创建ClusterStatusTracker对象，等待集群的启动，即等待master将zookeeper设置为up状态。
4.创建CatalogTracker对象，并启动它，从而获取-ROOT-和.META.的地址
停止：
关闭compactionChecker、cacheFlusher、hlogRoller、compactSplitThread、service、replicationHandler线程