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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-6389) Modify the conditions to ensure that Master waits for sufficient number of Region Servers before starting region assignments
Date Fri, 02 Nov 2012 19:25:14 GMT

     [ https://issues.apache.org/jira/browse/HBASE-6389?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

stack updated HBASE-6389:
-------------------------

    Release Note: 
Reverts the cluster startup behavior to pre 0.94.0.

With this, Master will wait until "hbase.master.wait.on.regionservers.mintostart" number of
Region Servers have registered with it before it starts region assignment. The default value
of this setting is 1.

In large clusters with thousands of regions you may want to increase this to a higher number
which is sufficient to handle the task of opening those region in parallel.

If left to the default, at times, the Master could assign all regions to a single Region Server
which will result in slow startup and in worst case could OOM the Region Server (some time
resulting in META inconsistency).

Here is how it works now (from the javadoc):

We wait until one of these 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

  was:
Reverts the cluster startup behavior to pre 0.94.0.

With this, Master will wait until "hbase.master.wait.on.regionservers.mintostart" number of
Region Servers have registered with it before it starts region assignment. The default value
of this setting is 1.

In large clusters with thousands of regions you may want to increase this to a higher number
which is sufficient to handle the task of opening those region in parallel.

If left to the default, at times, the Master could assign all regions to a single Region Server
which will result in slow startup and in worst case could OOM the Region Server (some time
resulting in META inconsistency).

    Hadoop Flags: Incompatible change,Reviewed

Committed to trunk.  Thanks for the clarifications Aditya (and the fix).  Lars, you want this
for 0.94.3?  I marked it as an 'incompatible change' but this is a bug fix, and the behavior
now more rational.
                
> 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: 0.94.3, 0.96.0
>
>         Attachments: HBASE-6389_0.94.patch, HBASE-6389_trunk.patch, HBASE-6389_trunk.patch,
HBASE-6389_trunk.patch, HBASE-6389_trunk_v2.patch, HBASE-6389_trunk_v2.patch, org.apache.hadoop.hbase.TestZooKeeper-output.txt,
testReplication.jstack
>
>
> 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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