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Date: Sat, 28 Jun 2014 19:41:24 +0000 (UTC)
From: "Jonathan Park (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 ]

Jonathan Park updated ACCUMULO-2889:
------------------------------------

    Attachment: accumulo-2889_withoutpatch.png
                accumulo-2889-withpatch.png
                ACCUMULO-2889.1.patch
                start-ingest.sh
                batch_perf_test.sh
                run_all.sh

Results from performance tests:

Test design:
- Run continuous ingest with 4 ingesters each ingesting 25million entries and then measure time until completion
- We varied # of minor compactors and tablets per server (in retrospect, # of minor compactors didn't really matter in these tests, it may have been better to vary # of clients).
- Each trial was run 3x and the average was taken.

Tests were run on a single node (24 logical cores, 64 GB RAM, 8 drives)

||minc||tablets/server||w/o patch(ms)||w/ patch(ms)||ratio||
|4|32|269790.33|257537.33|0.95458325|
|12|32|271124.33|255952|0.94403922|
|12|320|355962.67|323737|0.90946896|
|24|32|268709|261362.67|0.97266065|
|24|320|355182.33|324308.67|0.91307659|

I'll try to run this on a multi-node cluster if I can get around to it.

> 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-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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