[jira] [Commented] (HBASE-9132) Use table dir modtime to avoid scanning table dir to check cached table descriptor in 0.94

["Dave Latham (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-9132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13730173#comment-13730173 ] 

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

Here's a patch for 0.94.
Table descriptor read:
 - first check directory modtime against cached entry.
 - If directory has not changed, use cached entry.
 - Else, check the descriptor file modtime.
 - If the descriptor file has not changed, use it (and create a new cached entry with the updated directory modtime)
 - Else, read the new descriptor file.
                
> 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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