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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18056) Change CompactingMemStore in BASIC mode to merge multiple segments in pipeline
Date Sun, 21 May 2017 09:11:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018768#comment-16018768

Eshcar Hillel commented on HBASE-18056:

I think we are missing the point here.
The original need for merge in the pipeline was the degradation in *read* performance when
we didn't use merge.
The GC is not the issue here, but for sure we demonstrated in the benchmark that doing merge
is not increasing GC and has no negative effect on write performance https://issues.apache.org/jira/browse/HBASE-16417?focusedCommentId=15929565&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15929565

Using/not using MSLABs is also not the issue here since the merge is only at the index level,
it doesn't remove duplicates and its affect is the same whether data is stored on MSLABs or

+1 for this patch, it is only pushing a solution we already agreed on.
Without it we have a problem with the high percentiles of reads, and I didn't see any reasonable
explanation or evidence that it causes any  issues in any other settings.

> Change CompactingMemStore in BASIC mode to merge multiple segments in pipeline
> ------------------------------------------------------------------------------
>                 Key: HBASE-18056
>                 URL: https://issues.apache.org/jira/browse/HBASE-18056
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Anastasia Braginsky
>         Attachments: HBASE-18056-V01.patch
> Under HBASE-16417 it was decided that CompactingMemStore in BASIC mode should merge multiple
ImmutableSegments in CompactionPipeline. Basic+Merge actually demonstrated reduction in GC,
alongside improvement in other metrics.
> However, the limit on the number of segments in pipeline is still set to 30. Under this
JIRA it should be changed to 1, as it was tested under HBASE-16417.

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