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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ACCUMULO-1083) add concurrency to HDFS write-ahead log
Date Sat, 04 Apr 2015 02:28:33 GMT

     [ https://issues.apache.org/jira/browse/ACCUMULO-1083?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Josh Elser updated ACCUMULO-1083:
---------------------------------
    Fix Version/s:     (was: 1.7.0)

> add concurrency to HDFS write-ahead log
> ---------------------------------------
>
>                 Key: ACCUMULO-1083
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1083
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>            Reporter: Adam Fuchs
>         Attachments: walog-performance.jpg, walog-replication-factor-performance.jpg
>
>
> When running tablet servers on beefy nodes (lots of disks), the write-ahead log can be
a serious bottleneck. Today we ran a continuous ingest test of 1.5-SNAPSHOT on an 8-node (plus
a master node) cluster in which the nodes had 32 cores and 15 drives each. Running with write-ahead
log off resulted in a >4x performance improvement sustained over a long period.
> I believe the culprit is that the WAL is only using one file at a time per tablet server,
which means HDFS is only appending to one drive (plus replicas). If we increase the number
of concurrent WAL files supported on a tablet server we could probably drastically improve
the performance on systems with many disks. As it stands, I believe Accumulo is significantly
more optimized for a larger number of smaller nodes (3-4 drives).



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