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From "Dave Latham (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9132) Use table dir modtime to avoid scanning table dir to check cached table descriptor in 0.94
Date Tue, 06 Aug 2013 01:16:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13730241#comment-13730241
] 

Dave Latham commented on HBASE-9132:
------------------------------------

Thanks, Ted, for the comments.

{quote}nit: uppercase 'h'{quote}
That was following existing code that uses {{cachehits}} and {{cachedtdm}}.

{quote}Why passing false above ?{quote}
Because that method doesn't need the directory mod time, so passing false skips an extra roundtrip
to the NameNode.

                
> Use table dir modtime to avoid scanning table dir to check cached table descriptor in
0.94
> ------------------------------------------------------------------------------------------
>
>                 Key: HBASE-9132
>                 URL: https://issues.apache.org/jira/browse/HBASE-9132
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Dave Latham
>            Assignee: Dave Latham
>             Fix For: 0.94.12
>
>         Attachments: HBASE-9132-0.94.patch
>
>
> As described in HBASE-8778, anything that needs to read table descriptors (such as region
assignments) currently results in a table directory scan which is slow on tables with many
regions.  HBASE-8778 moved the table descriptors to a subdir for 0.96+.  For 0.94 a smaller
change that is safe with rolling restarts is to cache the directory modtime and use the cached
table descriptor if the directory modtime has not changed since a table descriptor change
always changes the directory.

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