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Date: Thu, 19 Jul 2012 03:07:36 +0000 (UTC)
From: "Aditya Kishore (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Updated] (HBASE-6389) Modify the conditions to ensure that
 Master waits for sufficient number of Region Servers before starting region
 assignments
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     [ https://issues.apache.org/jira/browse/HBASE-6389?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aditya Kishore updated HBASE-6389:
----------------------------------

    Attachment: HBASE-6389_trunk.patch

As suspected, the failure was result of a partial shutdown of region server expired in the previous test.

The region server thread of this expired server was still alive when the next test started which lead the test pre-condition to believe that enough number of RSes are available.

The new patch take care of the problem.
                
> 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}

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