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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10319) HLog should roll periodically to allow DN decommission to eventually complete.
Date Sat, 11 Jan 2014 02:15:50 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13868610#comment-13868610
] 

Andrew Purtell commented on HBASE-10319:
----------------------------------------

bq. Since no new data is ever written, the existing periodic check is not activated.

Then this has been a long standing bug, since it confounds expectations set up by hbase-default.xml:

{noformat}
  <property>
    <name>hbase.regionserver.logroll.period</name>
    <value>3600000</value>
    <description>Period at which we will roll the commit log regardless
    of how many edits it has.</description>
  </property>
{noformat}


> HLog should roll periodically to allow DN decommission to eventually complete.
> ------------------------------------------------------------------------------
>
>                 Key: HBASE-10319
>                 URL: https://issues.apache.org/jira/browse/HBASE-10319
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Jonathan Hsieh
>
> We encountered a situation where we had an esseitially read only table and attempted
to do a clean HDFS DN decommission.  DN's cannot decomission if there are open blocks being
written to currently on it.  Because the hbase Hlog file was open, had some data (hlog header),
the DN could not decommission itself.  Since no new data is ever written, the existing periodic
check is not activated.
> After discussing with [~atm], it seems that although an hdfs semantics change would be
ideal (e.g. hbase doesn't have to be aware of hdfs decommission and the client would roll
over) this would take much more effort than having hbase periodically force a log roll.  This
would enable the hdfs dn con complete.



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