hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Aditya Kishore (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6389) Modify the conditions to ensure that Master waits for sufficient number of Region Servers before starting region assignments
Date Thu, 19 Jul 2012 22:31:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418731#comment-13418731
] 

Aditya Kishore commented on HBASE-6389:
---------------------------------------

@Ted

The last patch address the exact issue listed at https://issues.apache.org/jira/browse/HBASE-6406?focusedCommentId=13417665&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13417665

What had happened is that in most test runs, the test testRegionServerSessionExpired() get
launched before testMasterSessionExpired() or testMasterZKSessionRecoveryFailure(). This test
testRegionServerSessionExpired() brings down one of the two region servers but this RS is
not dead by the time testMasterSessionExpired() or testMasterZKSessionRecoveryFailure() starts.

The precondition of each test evaluates and ensure than a minimum of two region servers are
online (by testing if their threads are "alive" and not by testing their ZK node or connecting
to it).

So while one of the RS is shutting itself down (and its thread is still alive), and either
of testMasterSessionExpired() or testMasterZKSessionRecoveryFailure() could start because
the test precondition is satisfied. However, both of these test cases result in Master recovery
and reinitialization which actually attempts to check for the quorum of 2 Online region servers
and since there is only one region server online at this point, the initialization fails with
timeout and the master is killed.

By this time the dying region server's thread is dead and the precondition of the next test
sees that it needs to create one region server. But since no master is running at this point,
the newly created region server's run thread gets blocked in HRegionServer.blockAndCheckIfStopped()
and the RS does not come online. As a result the test thread which is waiting for the RS to
come online keeps waiting which is why you see the test hung in setup().

My last patch ensured that the dying RS is completely stopped before testRegionServerSessionExpired()
completes so that the subsequent tests' precondition does not get fooled into thinking that
the minimum server count is met and start the testcase.
                
> Modify the conditions to ensure that Master waits for sufficient number of Region Servers
before starting region assignments
> ----------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-6389
>                 URL: https://issues.apache.org/jira/browse/HBASE-6389
>             Project: HBase
>          Issue Type: Bug
>          Components: master
>    Affects Versions: 0.94.0, 0.96.0
>            Reporter: Aditya Kishore
>            Assignee: Aditya Kishore
>            Priority: Critical
>             Fix For: 0.96.0, 0.94.2
>
>         Attachments: HBASE-6389_trunk.patch, HBASE-6389_trunk.patch, HBASE-6389_trunk.patch
>
>
> Continuing from HBASE-6375.
> It seems I was mistaken in my assumption that changing the value of "hbase.master.wait.on.regionservers.mintostart"
to a sufficient number (from default of 1) can help prevent assignment of all regions to one
(or a small number of) region server(s).
> While this was the case in 0.90.x and 0.92.x, the behavior has changed in 0.94.0 onwards
to address HBASE-4993.
> From 0.94.0 onwards, Master will proceed immediately after the timeout has lapsed, even
if "hbase.master.wait.on.regionservers.mintostart" has not reached.
> Reading the current conditions of waitForRegionServers() clarifies it
> {code:title=ServerManager.java (trunk rev:1360470)}
> ....
> 581	  /**
> 582	   * Wait for the region servers to report in.
> 583	   * We will wait until one of this condition is met:
> 584	   *  - the master is stopped
> 585	   *  - the 'hbase.master.wait.on.regionservers.timeout' is reached
> 586	   *  - the 'hbase.master.wait.on.regionservers.maxtostart' number of
> 587	   *    region servers is reached
> 588	   *  - the 'hbase.master.wait.on.regionservers.mintostart' is reached AND
> 589	   *   there have been no new region server in for
> 590	   *      'hbase.master.wait.on.regionservers.interval' time
> 591	   *
> 592	   * @throws InterruptedException
> 593	   */
> 594	  public void waitForRegionServers(MonitoredTask status)
> 595	  throws InterruptedException {
> ....
> ....
> 612	    while (
> 613	      !this.master.isStopped() &&
> 614	        slept < timeout &&
> 615	        count < maxToStart &&
> 616	        (lastCountChange+interval > now || count < minToStart)
> 617	      ){
> ....
> {code}
> So with the current conditions, the wait will end as soon as timeout is reached even
lesser number of RS have checked-in with the Master and the master will proceed with the region
assignment among these RSes alone.
> As mentioned in -[HBASE-4993|https://issues.apache.org/jira/browse/HBASE-4993?focusedCommentId=13237196#comment-13237196]-,
and I concur, this could have disastrous effect in large cluster especially now that MSLAB
is turned on.
> To enforce the required quorum as specified by "hbase.master.wait.on.regionservers.mintostart"
irrespective of timeout, these conditions need to be modified as following
> {code:title=ServerManager.java}
> ..
>   /**
>    * Wait for the region servers to report in.
>    * We will wait until one of this condition is met:
>    *  - the master is stopped
>    *  - the 'hbase.master.wait.on.regionservers.maxtostart' number of
>    *    region servers is reached
>    *  - the 'hbase.master.wait.on.regionservers.mintostart' is reached AND
>    *   there have been no new region server in for
>    *      'hbase.master.wait.on.regionservers.interval' time AND
>    *   the 'hbase.master.wait.on.regionservers.timeout' is reached
>    *
>    * @throws InterruptedException
>    */
>   public void waitForRegionServers(MonitoredTask status)
> ..
> ..
>     int minToStart = this.master.getConfiguration().
>     getInt("hbase.master.wait.on.regionservers.mintostart", 1);
>     int maxToStart = this.master.getConfiguration().
>     getInt("hbase.master.wait.on.regionservers.maxtostart", Integer.MAX_VALUE);
>     if (maxToStart < minToStart) {
>       maxToStart = minToStart;
>     }
> ..
> ..
>     while (
>       !this.master.isStopped() &&
>         count < maxToStart &&
>         (lastCountChange+interval > now || timeout > slept || count < minToStart)
>       ){
> ..
> {code}

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira

        

Mime
View raw message