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https://issues.apache.org/jira/browse/HBASE-8665?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sergey Shelukhin updated HBASE-8665:
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Status: Patch Available (was: Open)
> bad compaction priority behavior in queue can cause store to be blocked
> -----------------------------------------------------------------------
>
> Key: HBASE-8665
> URL: https://issues.apache.org/jira/browse/HBASE-8665
> Project: HBase
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Sergey Shelukhin
> Attachments: HBASE-8665-v0.patch
>
>
> Note that this can be solved by bumping up the number of compaction threads
> but still it seems like this priority "inversion" should be dealt with.
> There's a store with 1 big file and 3 flushes (1 2 3 4) sitting around and
> minding its own business when it decides to compact. Compaction (2 3 4) is
> created and put in queue, it's low priority, so it doesn't get out of the
> queue for some time - other stores are compacting. Meanwhile more files are
> flushed and at (1 2 3 4 5 6 7) it decides to compact (5 6 7). This compaction
> now has higher priority than the first one. After that if the load is high it
> enters vicious cycle of compacting and compacting files as they arrive, with
> store being blocked on and off, with the (2 3 4) compaction staying in queue
> for up to ~20 minutes (that I've seen).
> I wonder why we do thing thing where we queue compaction and compact
> separately. Perhaps we should take snapshot of all store priorities, then do
> select in order and execute the first compaction we find. This will need
> starvation safeguard too but should probably be better.
> Btw, exploring compaction policy may be more prone to this, as it can select
> files from the middle, not just beginning, which, given the treatment of
> already selected files that was not changed from the old ratio-based one (all
> files with lower seqNums than the ones selected are also ineligible for
> further selection), will make more files ineligible (e.g. imagine with 10
> blocking files, with 8 present (1-8), (6 7 8) being selected and getting
> stuck). Today I see the case that would also apply to old policy, but
> yesterday I saw file distribution something like this: 4,5g, 2,1g, 295,9m,
> 113,3m, 68,0m, 67,8m, 1,1g, 295,1m, 100,4m, unfortunately w/o enough logs to
> figure out how it resulted.
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