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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Assigned: (HBASE-1740) ICV has a subtle race condition only visible under high load
Date Thu, 10 Sep 2009 23:37:57 GMT

     [ https://issues.apache.org/jira/browse/HBASE-1740?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

ryan rawson reassigned HBASE-1740:
----------------------------------

    Assignee: ryan rawson

> ICV has a subtle race condition only visible under high load
> ------------------------------------------------------------
>
>                 Key: HBASE-1740
>                 URL: https://issues.apache.org/jira/browse/HBASE-1740
>             Project: Hadoop HBase
>          Issue Type: Bug
>    Affects Versions: 0.20.0
>            Reporter: ryan rawson
>            Assignee: ryan rawson
>             Fix For: 0.20.1
>
>         Attachments: HBASE-1740-test.patch, HBASE-1740.patch, HBASE-icv.patch
>
>
> ICV demonstrates a race condition under high load.  The result is a duplicate KeyValue
with the same timestamp, at first in the memcache, and in hfile, then both in hfile.  The
get/scan code doesnt know which one to read, and picks one arbitrarily.  One of the keyvalues
is correct, one is incorrect.
> What happens at a deeper level:
> - we start an ICV
> - a snapshot happens and moves the memstore to the snapshot
> - the ICV code puts a key-value into memstore that has the same timestamp as a keyvalue
in the snapshot.
> This is a deep race condition and several attempts to fix it failed in production here
at SU.  This issue is about a more permanent fix.

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