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From "Kelvin Kakugawa (JIRA)" <j...@apache.org>
Subject [jira] Updated: (CASSANDRA-1930) db.Table flusherLock write lock fairness policy is sub-optimal
Date Tue, 04 Jan 2011 01:26:46 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-1930?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kelvin Kakugawa updated CASSANDRA-1930:
---------------------------------------

    Attachment: CASSANDRA-1930.0001.patch

use default RRW lock policy

> db.Table flusherLock write lock fairness policy is sub-optimal
> --------------------------------------------------------------
>
>                 Key: CASSANDRA-1930
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1930
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.3, 0.4, 0.5, 0.6, 0.6.1, 0.6.2, 0.6.3, 0.6.4, 0.6.5, 0.6.6, 0.6.7,
0.6.8, 0.6.9, 0.7 beta 1, 0.7 beta 2, 0.7 beta 3, 0.7.0 rc 1, 0.7.0 rc 2, 0.7.0 rc 3, 0.7.0,
0.7.1, 0.8
>            Reporter: Kelvin Kakugawa
>            Assignee: Kelvin Kakugawa
>             Fix For: 0.8
>
>         Attachments: CASSANDRA-1930.0001.patch
>
>
> h4. scenario:
> 1) high write throughput cluster
> 2) external services adding material cpu contention
> h4. symptoms:
> The row mutation stage falls *very* behind.
> h4. cause:
> ReentrantReadWriteLock's fair policy causes write lock acquisition / release to require
a material amount of CPU time.
> h4. summary:
> When there are other services contending for the CPU, the RRW lock's fair policy causes
write lock acquisition / release to take enough time to eventually put threads waiting for
read lock acquisition very behind.  We repro'd this scenario by reducing the scope of the
write lock to: 1 boolean check, 1 boolean assignment, and 1 db.Memtable instantiation (itself,
just: 2 variable assignments) w/ the same performance.  Modifying the fairness policy to be
the default policy allowed the row mutation stage to keep up.

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