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From "Christopher Tubbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-4692) CompactionDriver leaves abandoned metadata scans
Date Fri, 04 Aug 2017 16:49:00 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-4692?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16114613#comment-16114613
] 

Christopher Tubbs commented on ACCUMULO-4692:
---------------------------------------------

[~milleruntime], when I took a look at the code, it looks like this affects 1.7+

I spoke to [~kturner] about this and he indicated that it would be hard to know exactly where
to end the scan, because you don't know the split points in advance for the given table range.
So, you don't know how many tablets metadata to read for that table. We talked about the possibility
of implementing the "close" method for scanner so that such scans could be terminated once
you've read all the data you want from the scanner.

> CompactionDriver leaves abandoned metadata scans
> ------------------------------------------------
>
>                 Key: ACCUMULO-4692
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-4692
>             Project: Accumulo
>          Issue Type: Bug
>          Components: fate
>            Reporter: Adam Fuchs
>
> We wrote a tool to kick off tablet compactions in the background while minimizing compaction
load per-server. The tool uses range compaction on one tablet per call. We're seeing a high
number of scans on the metadata table (~7,000 on a ~100 node cluster).
> The metadata query in the isReady() method of CompactionDriver that is used to see if
the compaction has completed uses a range that goes to the end of the metadata entries for
the given table, but it stops consuming the results of the scanner at the end of the compaction
range. isReady gets called in a pretty tight loop, especially with hundreds of compactions
running concurrently. Seems like we should limit the scan to the metadata range associated
with the compaction so that the scan can get cleaned up quickly.



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