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https://issues.apache.org/jira/browse/HBASE-15102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15097326#comment-15097326
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Ashu Pachauri commented on HBASE-15102:
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{quote} The value of step is modified inside the if block. This potentially
would result in mismatch between adjusts to memstore size and blockcache
size.{quote}
On the contrary, it won't. I modified the value of step deliberately instead of
directly manipulating the memstore and blockcache size, because the memstore
and block cache size are always adjusted by the value of step.
> HeapMemoryTuner can "overtune" memstore size and suddenly drop it into
> blocking zone
> ------------------------------------------------------------------------------------
>
> Key: HBASE-15102
> URL: https://issues.apache.org/jira/browse/HBASE-15102
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 2.0.0, 1.2.0, 1.3.0, 1.2.1
> Reporter: Ashu Pachauri
> Assignee: Ashu Pachauri
> Priority: Critical
> Attachments: HBASE-15102-V0.patch
>
>
> DefaultHeapMemoryTuner often resets the maximum step size for tuning to 8% of
> total heap size. Often, when the size of memstore is to be decreased while
> tuning, the 8% tuning can suddenly drop the memstore size below the low water
> mark of the previous memstore size (which could potentially be the used size
> of the memstore)
> This is problematic because suddenly it blocks all the updates by suddenly
> causing a situation where memstore used size is above high water mark. This
> has a very bad performance impact on an otherwise fine HBase cluster.
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