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https://issues.apache.org/jira/browse/HBASE-6389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418160#comment-13418160
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nkeywal commented on HBASE-6389:
--------------------------------
bq. What's the general thought here? Reapply the patch? The timeout after the
patch is not really a timeout any longer, so at the very least the config
option is misnamed now. Or in different words: What is the point of this
timeout now?
After some thinking about it:
- if you want the exact same behavior as proposed by the patch you wan set
hbase.master.wait.on.regionservers.timeout and
hbase.master.wait.on.regionservers.interval to a high value
- if you want to fix the problem mentioned in this patch we could solve it by
throwing an exception when hbase.master.wait.on.regionservers.timeout is
reached. This would require to increase the default as Aditya said it above.
On a side note, I wonder what would be the impact when you're loosing a large
part of your servers. Someone setting this value to its exact number of nodes
will be disappointed.
> 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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