[HBASE-22810] Initialize an separate ThreadPoolExecutor for taking/restoring snapshot

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-1, 1.5.0, 2.3.0, 2.2.1, 2.1.6, 1.3.6, 1.4.11
• Hadoop Flags: Reviewed
• Release Note: Introduced a new config key for the snapshot taking/restoring operations at master side: hbase.master.executor.snapshot.threads, its default value is 3. means we can have 3 snapshot operations running at the same time.
• Assignee: Zheng Hu
• Reporter: Zheng Hu
• Created: 07/Aug/19 06:59
• Updated: 22/Aug/19 22:11
• Resolved: 22/Aug/19 05:46

Description

In EventType class, we have the following definition, means taking snapshot & restoring snapshot are use the MASTER_TABLE_OPERATIONS Executor now.

  /**
   * Messages originating from Client to Master.<br>
   * C_M_SNAPSHOT_TABLE<br>
   * Client asking Master to snapshot an offline table.
   */
  C_M_SNAPSHOT_TABLE        (48, ExecutorType.MASTER_TABLE_OPERATIONS),
  /**
   * Messages originating from Client to Master.<br>
   * C_M_RESTORE_SNAPSHOT<br>
   * Client asking Master to restore a snapshot.
   */
  C_M_RESTORE_SNAPSHOT      (49, ExecutorType.MASTER_TABLE_OPERATIONS),

But when I checked the MASTER_TABLE_OPERATIONS thread pool initialization, I see :

  private void startServiceThreads() throws IOException{
   // ...  some other code initializing .... 

   // We depend on there being only one instance of this executor running
   // at a time.  To do concurrency, would need fencing of enable/disable of
   // tables.
   // Any time changing this maxThreads to > 1, pls see the comment at
   // AccessController#postCompletedCreateTableAction
   this.executorService.startExecutorService(ExecutorType.MASTER_TABLE_OPERATIONS, 1);
   startProcedureExecutor();

That's to say, for CPs enable or disable table sequencely, we will create a ThreadPoolExecutor with threadPoolSize=1. Then we actually cann't accomplish the snapshoting concurrence even if they are total difference tables, says if there are two table snapshoting request, and the Table A cost 5min for snapshoting, then the Table B need to wait 5min and once Table A finish its snapshot , then Table B will start the snapshot.

While we've setting the snapshot timeout, so it will be easy to timeout for table B snapshoting . Actually, we can create a separate thead pool for snapshot operations only.

Issue Links

• breaks: HBASE-22901 TestFlushSnapshotFromClient is failing
• is related to: HBASE-22882 TestFlushSnapshotFromClient#testConcurrentSnapshottingAttempts is flakey (was written flakey)
• links to: GitHub Pull Request #486
• links to: GitHub Pull Request #517