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Date: Thu, 9 Jul 2015 22:51:05 +0000 (UTC)
From: "Josh Elser (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (ACCUMULO-2889) Batch metadata table updates for
 new walogs
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     [ https://issues.apache.org/jira/browse/ACCUMULO-2889?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Josh Elser updated ACCUMULO-2889:
---------------------------------
    Resolution: Incomplete
        Status: Resolved  (was: Patch Available)

This needs some more love. With Eric's recent changes to how WALs are recorded in the metadata table, it may invalidate the approach this patch was going. Feel free to reopen if desired.

> Batch metadata table updates for new walogs
> -------------------------------------------
>
>                 Key: ACCUMULO-2889
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2889
>             Project: Accumulo
>          Issue Type: Improvement
>    Affects Versions: 1.5.1, 1.6.0
>            Reporter: Jonathan Park
>            Assignee: Jonathan Park
>         Attachments: ACCUMULO-2889.0.patch.txt, ACCUMULO-2889.1.patch, ACCUMULO-2889.2.patch, accumulo-2889-withpatch.png, accumulo-2889_withoutpatch.png, batch_perf_test.sh, run_all.sh, start-ingest.sh
>
>
> Currently, when we update the Metadata table with new loggers, we will update the metadata for each tablet serially. We could optimize this to instead use a batchwriter to send all metadata updates for all tablets in a batch.
> A few special cases include:
> - What if the !METADATA tablet was included in the batch?
> - What about the root tablet?
> Benefit:
> In one of our clusters, we're experiencing particularly slow HDFS operations leading to large oscillations in ingest performance. We haven't isolated the cause in HDFS but when we profile the tservers, we noticed that they were waiting for metadata table operations to complete. This would target the waiting.
> Potential downsides:
> Given the existing locking scheme, it looks like we may have to lock a tablet for slightly longer (we'll lock for the duration of the batch).


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