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From "Edward Bortnikov (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 19:21:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018956#comment-16018956

Edward Bortnikov commented on HBASE-18056:


I'm having a hard time understanding why this commit became a big deal :) We made a mistake.
This parameter change should have been committed together with BASIC compaction becoming the
default configuration. BASIC does not make sense without it. We presented a vey extensive
perf evaluation exactly with this parameter value. It demonstrated improvement in all the
operational metrics, GC included. The parameter should be not accessible to users; it is not
documented in the reference manual; its sole purpose is developer flexibility. 

It is perfectly okay to re-open the discussion (and also revert the setting) once there is
solid proof that something is broken. But we didn't see any such proof yet. Delaying without
reason jeopardizes the feature, especially in anticipation of release.

Just saying it again - we made a technical mistake, and we are fixing it now. There is no
new data.  

What is it that I get wrong? Thanks. 

> 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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