Hbase 源码分析4 - Get 流程及rpc原理

分析版本为hbase 0.94

附上趋势团队画的图：

rpc角色表：

HBase通信信道	HBase的通信接口
客户端	服务端
HBase Client	Master Server	HMasterInterface
HBase Client	Region Server	HRegionInterface
Region Server	Master Server	HMasterRegionInterface

客户端发起请求：

htable.get(Get)

public Result get(final Get get) throws IOException {
return new ServerCallable<Result>(connection, tableName, get.getRow(), operationTimeout) {
public Result call() throws IOException {
return server.get(location.getRegionInfo().getRegionName(), get);
}
}.withRetries();
}

调用get方法后，客户端进入睡眠，睡眠时间为pause * HConstants.RETRY_BACKOFF[ntries];

pause=HBASE_CLIENT_PAUSE（1秒）

RETRY_BACKOFF[] = { 1, 1, 1, 2, 2, 4, 4, 8, 16, 32 };

有结果则中断执行返回rpc结果，否则重试十次（默认DEFAULT_HBASE_CLIENT_RETRIES_NUMBER=10）

通过HConnectionManager的getHRegionConnection方法获取连接

通过HRegionServer的get方法获取结果

服务器端：

当regionserver 收到来自客户端的Get请求时，调用接口

public Result get(byte[] regionName, Get get) 
{ 
... 
HRegion region = getRegion(regionName); 
return region.get(get, getLockFromId(get.getLockId())); 
... 
} 

在HRegion中

Scan scan = new Scan(get);
会先根据设置的columnFamily存放familyMap对 ---- columnFamily:null

public Get addFamily(byte [] family) {
familyMap.remove(family);
familyMap.put(family, null);
return this;
}

如果查询的family不在htableDescriptor中，返回错误

scanner = getScanner(scan);
public RegionScanner getScanner(Scan scan) throws IOException {
return getScanner(scan, null);
}

additionalScanners为null 所以在RegionScannerImpl的构造中只会使用StoreScanner

return instantiateRegionScanner(scan, additionalScanners);
return new RegionScannerImpl(scan, additionalScanners);

RegionScannerImpl 是 HRegion中的子类

for (Map.Entry<byte[], NavigableSet<byte[]>> entry :
scan.getFamilyMap().entrySet()) {
Store store = stores.get(entry.getKey());
StoreScanner scanner = store.getScanner(scan, entry.getValue());
scanners.add(scanner);
}

按照familyMap的数量存放对应数量的 StoreScanner

Hregion initialize时会对应每个columnFamily存放一个stores
Future<Store> future = completionService.take();
Store store = future.get();
this.stores.put(store.getColumnFamilyName().getBytes(), store);

scanners 添加从Store中获取的scanner

store.getScanners(cacheBlocks, isGet,
isCompaction, matcher)

Store 类：

memStoreScanners = this.memstore.getScanners();
List<StoreFileScanner> sfScanners = StoreFileScanner
.getScannersForStoreFiles(storeFiles, cacheBlocks, isGet, isCompaction, matcher);
List<KeyValueScanner> scanners =
new ArrayList<KeyValueScanner>(sfScanners.size()+1);
scanners.addAll(sfScanners);
// Then the memstore scanners
scanners.addAll(memStoreScanners);
return scanners;

memStoreScanners 为Collections.<KeyValueScanner>singletonList(
new MemStoreScanner())

Store中为StoreScanner添加了StoreFileScanner和memStoreScanner

进行scan时

scanner = getScanner(scan);
scanner.next(results);

现在分析RegionScannerImpl中的next方法，此时正式进入获取数据流程

@Override
public synchronized boolean next(List<KeyValue> outResults)
throws IOException {
// apply the batching limit by default
return next(outResults, batch);
}

batch默认为-1

startRegionOperation();

outResults.addAll(results);

startRegionOperation 会为操作加读锁，lock.readLock().lock();

然后遍历storeHeap，找到对应Row

do {
this.storeHeap.next(results, limit - results.size());
} while (Bytes.equals(currentRow, nextRow = peekRow()));

this.storeHeap 会不断poll出存储的scanner

因RegionScannerImpl 中memStoreScanners后添加，所以会先从memStoreScanners中查询，如果没有则从StoreFileScanner中查询

RegionScannerImpl 的storeHeap为KeyValueHeap，会强制转型scanner为InternalScanner

InternalScanner currentAsInternal = (InternalScanner)this.current;

总结下目前流程get request -> regionServer -> region -> storeHeap->scanner -> find row

但上述流程没有解释reguest是怎么找到regionServer去处理请求的，下边我们在分析下

服务器端服务在HMaster和HRegionServer启动时，中都会生成一个全局的RpcServer

hmaster的rpc server：

hmaster会使用org.apache.hadoop.hbase.executor.ExecutorService启动多种线程服务 （This is a generic executor service. This component abstracts a threadpool, a queue to whichEventHandler.EventTypes can be submitted, and a Runnable that handles the object that is added to the queue.）：

MASTER_OPEN_REGION （默认5）

MASTER_CLOSE_REGION （默认5）

MASTER_SERVER_OPERATIONS （默认3）

MASTER_META_SERVER_OPERATIONS （默认5）

MASTER_TABLE_OPERATIONS （单线程）

logCleaner（单线程）

infoServer (master-status 等信息展示)

rpcServer （我们需要用的rpc服务）

RpcServer是个接口，实现类为HBaseServer，启动时会开启responderlistenerhandlers几种类去响应请求，如设置了priorityHandlers的数目，会另外启动priorityHandlers，listener监听端口，提供请求给handlers，handlers则调用RpcEngine，反射出需要的方法并执行，通过responder写结果回去（this.responder.doRespond）。

HMaster的handlers的个数由hbase.master.handler.count

HRegionServer的handlers的个数由hbase.regionserver.handler.count 指定

HRegionServer的启动和HMaster类似，它启动以下线程：

this.service = new ExecutorService(getServerName().toString());
this.service.startExecutorService(ExecutorType.RS_OPEN_REGION,
conf.getInt("hbase.regionserver.executor.openregion.threads", 3));
this.service.startExecutorService(ExecutorType.RS_OPEN_ROOT,
conf.getInt("hbase.regionserver.executor.openroot.threads", 1));
this.service.startExecutorService(ExecutorType.RS_OPEN_META,
conf.getInt("hbase.regionserver.executor.openmeta.threads", 1));
this.service.startExecutorService(ExecutorType.RS_CLOSE_REGION,
conf.getInt("hbase.regionserver.executor.closeregion.threads", 3));
this.service.startExecutorService(ExecutorType.RS_CLOSE_ROOT,
conf.getInt("hbase.regionserver.executor.closeroot.threads", 1));
this.service.startExecutorService(ExecutorType.RS_CLOSE_META,
conf.getInt("hbase.regionserver.executor.closemeta.threads", 1));

hlogRoller(daemon)

cacheFlusher(daemon)

compactionChecker(daemon)

Leases(它不是线程，会启动后台线程)

splitLogWorker

rpcServer

HBaseClient 和 HMaster关系由HMasterInterface描述：

Clients interact with the HMasterInterface to gain access to meta-level
HBase functionality, like finding an HRegionServer and creating/destroying
tables.

HBaseClient 和 HRegionServer关系由HRegionInterface描述：

Clients interact with HRegionServers using a handleto the HRegionInterface

参考资料：

http://zjushch.iteye.com/blog/1173304

http://www.spnguru.com/2010/07/hbase-%E6%BA%90%E7%A0%81%E5%88%86%E6%9E%90-rpc%E6%9C%BA%E5%88%B6-%E5%9F%BA%E7%A1%80/