Aditya Kishore created HBASE-6389:
-------------------------------------
Summary: Modify the conditions to ensure that Master waits for
suffcient 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
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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