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From "Jim Kellerman (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1644) [hbase] Compactions should not block updates
Date Fri, 03 Aug 2007 17:10:53 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1644?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jim Kellerman updated HADOOP-1644:
----------------------------------

        Fix Version/s: 0.15.0
             Priority: Major  (was: Minor)
           Issue Type: Improvement  (was: Wish)
    Affects Version/s: 0.15.0
              Summary: [hbase] Compactions should not block updates  (was: [hbase] Compactions
should take no longer than period between memcache flushes)

> [hbase] Compactions should not block updates
> --------------------------------------------
>
>                 Key: HADOOP-1644
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1644
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: contrib/hbase
>    Affects Versions: 0.15.0
>            Reporter: stack
>            Assignee: stack
>             Fix For: 0.15.0
>
>
> Currently, compactions take a long time.  During compaction, updates are carried by the
HRegions' memcache (+ backing HLog).  memcache is unable to flush to disk until compaction
completes.
> Under sustained, substantial --  rows that contain multiple columns one of which is a
web page -- updates by multiple concurrent clients (10 in this case), a common hbase usage
scenario, the memcache grows fast and often to orders of magnitude in excess of the configured
'flush-to-disk' threshold.
> This throws the whole system out of kilter.  When memcache does get to run after compaction
completes -- assuming you have sufficent RAM and the region server doesn't OOME -- then the
resulting on-disk file will be way larger than any other on-disk HStoreFile bringing on a
region split ..... but the resulting split will produce regions that themselves need to be
immediately split because each half is beyond the configured limit, and so on...
> In another issue yet to be posted, tuning and some pointed memcache flushes makes the
above condition less extreme but until compaction durations come close to the memcache flush
threshold compactions will remain disruptive. 
> Its allowed that compactions may never be fast enough as per bigtable paper (This is
a 'wish' issue).

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