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https://issues.apache.org/jira/browse/HBASE-17178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15705686#comment-15705686
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Yu Li commented on HBASE-17178:
-------------------------------
{code}
+ int maxRegionsInTransition = getMaxRegionsInTransition();
{code}
Move this line out of synchronized, like {{maximumBalanceTime}}
{code}
+ // Throttling by max number regions in transition
+ while (!interrupted
+ && maxRegionsInTransition > 0
+ &&
this.assignmentManager.getRegionStates().getRegionsInTransitionCount()
+ >= maxRegionsInTransition) {
+ try {
+ // sleep if the number of regions in transition exceeds the limit
+ Thread.sleep(100);
+ } catch (InterruptedException ie) {
+ interrupted = true;
+ }
+ }
{code}
Two questions on this part inside {{balanceThrottling}}:
1. Shall the balancing be affected by other RIT? Assuming RS crash happened in
middle of balancing, shall we wait?
2. If some fatal error happens and cause some regions in transition for a long
time, the code flow of balancer might block here and not controlled by the
{{cutoffTime}}?
And maybe upload the patch into RB will make the review/comment easier (smile),
thanks.
> Add region balance throttling
> -----------------------------
>
> Key: HBASE-17178
> URL: https://issues.apache.org/jira/browse/HBASE-17178
> Project: HBase
> Issue Type: Improvement
> Components: Balancer
> Reporter: Guanghao Zhang
> Assignee: Guanghao Zhang
> Attachments: HBASE-17178-v1.patch, HBASE-17178-v2.patch,
> HBASE-17178-v3.patch
>
>
> Our online cluster serves dozens of tables and different tables serve for
> different services. If the balancer moves too many regions in the same time,
> it will decrease the availability for some table or some services. So we add
> region balance throttling on our online serve cluster.
> We introduce a new config hbase.balancer.max.balancing.regions, which means
> the max number of regions in transition when balancing.
> If we config this to 1 and a table have 100 regions, then the table will have
> 99 regions available at any time. It helps a lot for our use case and it has
> been running a long time
> our production cluster.
> But for some use case, we need the balancer run faster. If a cluster has 100
> regionservers, then it add 50 new regionservers for peak requests. Then it
> need balancer run as soon as
> possible and let the cluster reach a balance state soon. Our idea is compute
> max number of regions in transition by the max balancing time and the average
> time of region in transition.
> Then the balancer use the computed value to throttling.
> Examples for understanding.
> A cluster has 100 regionservers, each regionserver has 200 regions and the
> average time of region in transition is 1 seconds, we config the max
> balancing time is 10 * 60 seconds.
> Case 1. One regionserver crash, the cluster at most need balance 200 regions.
> Then 200 / (10 * 60s / 1s) < 1, it means the max number of regions in
> transition is 1 when balancing. Then the balancer can move region one by one
> and the cluster will have high availability when balancing.
> Case 2. Add other 100 regionservers, the cluster at most need balance 10000
> regions. Then 10000 / (10 * 60s / 1s) = 16.7, it means the max number of
> regions in transition is 17 when balancing. Then the cluster can reach a
> balance state within the max balancing time.
> Any suggestions are welcomed.
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