HBase disable table的过程
hbase的table delete之前需要将该table disable，今天结合源码分析一下disable的过程
?
首先看客户端HbaseAdmin.java中有接口
public void disableTable(final byte [] tableName)
public void disableTable(final String tableName)
?它们的实现都是
? public void disableTableAsync(final byte [] tableName) throws IOException {??? isMasterRunning();??? try {????? getMaster().disableTable(tableName);??? } catch (RemoteException e) {????? throw e.unwrapRemoteException();??? }??? LOG.info("Started disable of " + Bytes.toString(tableName));? }这段代码的主要过程是通过rpc远程调用执行HMaster的disableTable();
?所以我直接看HMaster的disableTable函数
public void disableTable(final byte [] tableName) throws IOException { this.executorService.submit(new DisableTableHandler(this, tableName, catalogTracker, assignmentManager)); }?起了一个新线程DisableTableHadnler
首先判断meta表中是否存在该table，扫描meta表，若meta表不存在table则返回，抛出异常tablenotexist
该线程主要调用
private void handleDisableTable()
?将zk上面的/table/?tablename标识为DISABLING
this.assignmentManager.getZKTable().setDisablingTable(this.tableNameStr);
boolean done = false; while (true) { // Get list of online regions that are of this table. Regions that are // already closed will not be included in this list; i.e. the returned // list is not ALL regions in a table, its all online regions according to // the in-memory state on this master. final List<HRegionInfo> regions = this.assignmentManager.getRegionsOfTable(tableName); if (regions.size() == 0) { done = true; break; } LOG.info("Offlining " + regions.size() + " regions."); BulkDisabler bd = new BulkDisabler(this.server, regions); try { if (bd.bulkAssign()) { done = true; break; } } catch (InterruptedException e) { LOG.warn("Disable was interrupted"); // Preserve the interrupt. Thread.currentThread().interrupt(); break; } } // Flip the table to disabled if success. if (done) this.assignmentManager.getZKTable().setDisabledTable(this.tableNameStr);?获取该table上的所有online的region集合。
对于这些regions? bulkassign：起20个线程对所有region进行unassigned
protected void populatePool(ExecutorService pool) { for (HRegionInfo region: regions) { if (assignmentManager.isRegionInTransition(region) != null) continue; final HRegionInfo hri = region; pool.execute(new Runnable() { public void run() { assignmentManager.unassign(hri); } }); } }?如上所示如果该Region已经在master的RIT队列中，则说明该region正在被处理，则忽略之
下面我们来看unassigned过程：
1.? 该region必须online，在master的online队列中存在
2.? 若该region在master的RIT队列中，且其state的状态是PENDING且force=true即表示即使该region正在closing ，force参数指定该region should be closed；
???? 若在RIT中且不符合上面条件则忽略返回；
???? 若不存在则将当前Region加入RIT队列中
3.? serverManager.sendRegionClose(server, state.getRegion())，Master端与该Region所在RS进行通信，RPC调用HRegionServer的closeRegion(region)函数
?
HRegionServer端
closeRegion(region)
1. 该region在RS的online regions列表上
2. 起一个线程CloseRegionhandler实现以下步骤
??? 1)setClosingState，在zk上创建unassigned下的该region节点将其值置为RS_ZK_REGION_CLOSING
??? 2)region.close(abort),关闭region，主要是关闭region下每个Store的每个HFile的reader
??? 3)将region从当前online列表中移除
??? 4)在zk上将该节点置为RS_ZK_REGION_CLOSED
????5)从RS的RIT队列中移除该region
Server端的主要逻辑即为如上所示
?
在上面过程中由于对zk上的unassigned节点进行了created和changed，且master端watch了该节点，当这些节点发生变化时会使得Master端也发生变化。
1)created时
public void nodeCreated(String path) { if(path.startsWith(watcher.assignmentZNode)) { synchronized(regionsInTransition) { try { RegionTransitionData data = ZKAssign.getData(watcher, path); if(data == null) { return; } handleRegion(data); } catch (KeeperException e) { master.abort("Unexpected ZK exception reading unassigned node data", e); } } } }?handleRegion的过程是将Master的RIT队列中该region的state置为CLOSING
2)变成Closed时
handleRegion将该region的state置为CLOSED然后力气一个线程CloseRegionHandler，此时如果zk上面/table下存在该table的节点，那么offlineDisabledRegion(HRegionInfo regionInfo)
??? 1.删除zk上的unassigned节点，
??? 2.clear regionplan
??? 3.从Master的online region和server上移除该region
??? 4.RIT中移除
?
?
整个过程结束。首先与hmaster进行通信，而后hmaster和rs进行通信，关闭region上各个HStore的Hfile的reader，在这个过程中涉及zk上节点的变化，master亦有相应的改变。