hbase 源代码解析（23）truncate 和truncate_preserve流程分析

原文地址：http://blog.csdn.net/chenfenggang/article/details/78335970

命令作用：清空表数据，但是保留表结构，
分析原因：今天定位一个奇怪的现象，当hbase建立4个region的表，然后用truncate命令时，出现1个region在线而有4个region offline，然后继续put数据，制定split到4个region时，使用truncate_preserve发现出现9个offline，7个failed，并且再put数据时出现表不存在，问题还在定位中。所以需要分析源码。
1）truncate shell命令入口
[code]module Shell
module Commands
class Truncate < Command
def help
return <<-EOF
Disables, drops and recreates the specified table.
EOF
end
def command(table)
format_simple_command do
puts "Truncating '#{table}' table (it may take a while):"
admin.truncate(table) { |log| puts " - #{log}" }
end
end
end
end
end
[/code]

2）客户端有HBaseAdmin 发起，经MasterRpcServices转接，由HMaster执行，主要代码如下：preserveSplits是命令truncate_preserve时，保留region个数。否则region变为1.

MasterProcedureUtil.submitProcedure(

new MasterProcedureUtil.NonceProcedureRunnable(this, nonceGroup, nonce) {

@Override

protected void run() throws IOException {

getMaster().getMasterCoprocessorHost().preTruncateTable(tableName);

LOG.info(getClientIdAuditPrefix() + " truncate " + tableName);

long procId = submitProcedure(new TruncateTableProcedure(procedureExecutor.getEnvironment(),

tableName, preserveSplits));

ProcedureSyncWait.waitForProcedureToComplete(procedureExecutor, procId);

getMaster().getMasterCoprocessorHost().postTruncateTable(tableName);

}

[/code]这里可以分两步，第一个submitProcedure怎么运行的。第二个truncateTableprocedure里的具体流程是什么1、submitProcedure这个流程主要如下：1）从Hmaster获取ProcedureExecutor2）ProcedureExecutor 是在HMaster 启动时执行的startProcedureExecutor();3）startProcedureExecutor里面调用了，procedureExecutor.start(numThreads, abortOnCorruption);4）start里面调用一个循环execLoop(); ----（类ProcedureExecutor中）5）execLoop里面是循环，不断从集合（ProcedureRunnableSet runnables）里拿到进程然后执行（execLoop(proc);）6）execLoop(proc)主要执行 execProcedure(procStack, proc); ----（类ProcedureExecutor中）7）最终会调用 procedure.doExecute(getEnvironment());8）doExecute 会调用execute(env); （类Procedure中）

9）在execute(env)中会调用 executeFromState （类StateMachineProcedure中）

所以只需要关心procedure的executeFromState方法就行。2、TruncateTableprocedure在这个类里面主要关心方法executeFromState：1）TRUNCATE_TABLE_PRE_OPERATION(0, 1), 准备动作：regions=ProcedureSyncWait.getRegionsFromMeta(env,getTableName());这里还做了写协处理器问题。getRegionsFromMeta就只一个查询动作2）TRUNCATE_TABLE_REMOVE_FROM_META(1, 2),在META表中删除数据：DeleteTableProcedure.deleteFromMeta(env,getTableName(),regions);这个就是一些delete操作3）TRUNCATE_TABLE_CLEAR_FS_LAYOUT(2, 3),清除File：DeleteTableProcedure.deleteFromFs(env,getTableName(),regions,true);这里主要注意的是如果设置里归档，会将记录进行归档，否则直接会删除重新创建regionInfo：regions=recreateRegionInfo(regions);这里如果保留regions的分区，采用的这个方法，如果不是，就直接new一个regionInfo startkey 和endkey都为null4）TRUNCATE_TABLE_CREATE_FS_LAYOUT(3, 4),重新创建FS目录，主要根据region建立：regions=CreateTableProcedure.createFsLayout(env,hTableDescriptor,regions);5）TRUNCATE_TABLE_ADD_TO_META(4, 5),将新的region信息添加到META表：regions =CreateTableProcedure.addTableToMeta(env,hTableDescriptor,regions);6）TRUNCATE_TABLE_ASSIGN_REGIONS(5, 6),分配region给regionServer：CreateTableProcedure.assignRegions(env,getTableName(),regions);这个是createTable必须做的事情。7）TRUNCATE_TABLE_POST_OPERATION(6, 7),处理一些协处理器： postTruncate(env);完整代码如下：

@Override

protected Flow executeFromState(final MasterProcedureEnv env, TruncateTableState state)

throws InterruptedException {

try {

switch (state) {

case TRUNCATE_TABLE_PRE_OPERATION:

// Verify if we can truncate the table

if (!prepareTruncate(env)) {

assert isFailed() : "the truncate should have an exception here";

return Flow.NO_MORE_STATE;

}

// TODO: Move out... in the acquireLock()

LOG.debug("waiting for '" + getTableName() + "' regions in transition");

regions = ProcedureSyncWait.getRegionsFromMeta(env, getTableName());

assert regions != null && !regions.isEmpty() : "unexpected 0 regions";

ProcedureSyncWait.waitRegionInTransition(env, regions);

// Call coprocessors

preTruncate(env);

setNextState(TruncateTableState.TRUNCATE_TABLE_REMOVE_FROM_META);

break;

case TRUNCATE_TABLE_REMOVE_FROM_META:

hTableDescriptor = env.getMasterServices().getTableDescriptors().get(tableName);

DeleteTableProcedure.deleteFromMeta(env, getTableName(), regions);

DeleteTableProcedure.deleteAssignmentState(env, getTableName());

setNextState(TruncateTableState.TRUNCATE_TABLE_CLEAR_FS_LAYOUT);

break;

case TRUNCATE_TABLE_CLEAR_FS_LAYOUT:

DeleteTableProcedure.deleteFromFs(env, getTableName(), regions, true);

if (!preserveSplits) {

// if we are not preserving splits, generate a new single region

regions = Arrays.asList(ModifyRegionUtils.createHRegionInfos(hTableDescriptor, null));

} else {

regions = recreateRegionInfo(regions);

}

setNextState(TruncateTableState.TRUNCATE_TABLE_CREATE_FS_LAYOUT);

break;

case TRUNCATE_TABLE_CREATE_FS_LAYOUT:

regions = CreateTableProcedure.createFsLayout(env, hTableDescriptor, regions);

CreateTableProcedure.updateTableDescCache(env, getTableName());

setNextState(TruncateTableState.TRUNCATE_TABLE_ADD_TO_META);

break;

case TRUNCATE_TABLE_ADD_TO_META:

regions = CreateTableProcedure.addTableToMeta(env, hTableDescriptor, regions);

setNextState(TruncateTableState.TRUNCATE_TABLE_ASSIGN_REGIONS);

break;

case TRUNCATE_TABLE_ASSIGN_REGIONS:

CreateTableProcedure.assignRegions(env, getTableName(), regions);

setNextState(TruncateTableState.TRUNCATE_TABLE_POST_OPERATION);

hTableDescriptor = null;

regions = null;

break;

case TRUNCATE_TABLE_POST_OPERATION:

postTruncate(env);

LOG.debug("truncate '" + getTableName() + "' completed");

return Flow.NO_MORE_STATE;

default:

throw new UnsupportedOperationException("unhandled state=" + state);

}

} catch (HBaseException|IOException e) {

LOG.warn("Retriable error trying to truncate table=" + getTableName() + " state=" + state, e);

}

return Flow.HAS_MORE_STATE;

}

[/code] http://blog.csdn.net/chenfenggang/article/details/78335970