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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8299) ExploringCompactionPolicy can get stuck in rare cases.
Date Tue, 09 Apr 2013 22:02:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627177#comment-13627177

Sergey Shelukhin commented on HBASE-8299:

I get that it needs to be fixed, but this fix affects the cases beyond the ones it's looking
to solve, so I am looking for another, or modified, fix.

This fix changes the logic of requestCompaction to force compaction   every time it's called
when needsCompaction is true, which is different from current behavior (and that for old default
policy) where needsCompaction is an inaccurate pre-check and real decision is done in requestCompaction,
which is called speculatively form many place. Changing semantics of requestCompaction like
that will cause bad compactions in normal cases where compaction is not needed. 
Including bad consequences with many compactions (see compaction checker - how it runs compactions).
I am looking to avoid that.

The ways to avoid it that can be used are:
1) Keep this patch but add force flag/method which will trigger this  behavior of "select
compaction regardless of ratio".
2) Change semantics of needsCompaction and requestCompaction across the code so that the assumption
this patch makes is actually true.
3) Change the heuristic to not get stuck in such case via other means.

It seems that (1) is the simplest. 
> ExploringCompactionPolicy can get stuck in rare cases.
> ------------------------------------------------------
>                 Key: HBASE-8299
>                 URL: https://issues.apache.org/jira/browse/HBASE-8299
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.95.1
>            Reporter: Elliott Clark
>            Assignee: Elliott Clark
>         Attachments: HBASE-8299-0.patch
> If the files are very oddly sized then it's possible that ExploringCompactionPolicy can
get stuck.

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