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From "Samarth Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-4021) Remove CachingHTableFactory
Date Fri, 14 Jul 2017 02:24:02 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-4021?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16086739#comment-16086739
] 

Samarth Jain commented on PHOENIX-4021:
---------------------------------------

Before we go down the route of caching an HConnection, it would be good to confirm that if
an HConnection gets into a funky state, then internal logic will get it back in a usable state
(through retries, establishing new ZK session, etc.)

> Remove CachingHTableFactory
> ---------------------------
>
>                 Key: PHOENIX-4021
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4021
>             Project: Phoenix
>          Issue Type: Bug
>    Affects Versions: 4.11.0
>            Reporter: Geoffrey Jacoby
>            Assignee: Geoffrey Jacoby
>              Labels: globalMutableSecondaryIndex
>             Fix For: 4.12.0
>
>         Attachments: PHOENIX-4021.patch
>
>
> CachingHTableFactory is used as a performance optimization when writing to global indexes
so that HTable instances are cached and later automatically cleaned up, rather than instantiated
each time we write to an index.
> This should be removed for two reasons:
> 1. It opens us up to race conditions, because HTables aren't threadsafe, but CachingHTableFactory
doesn't guard against two threads both grabbing the same HTable and using it simultaneously.
Since all ops going through a region share the same IndexWriter and ParallelWriterIndexCommitter,
and hence the same CachingHTableFactory, that means separate operations can both be holding
the same HTable. 
> 2. According to discussion on PHOENIX-3159, and offline discussions I've had with [~apurtell],
HBase 1.x and above make creating throwaway HTable instances cheap so the caching is no longer
needed.
> For 4.x-HBase-1.x and master, we should remove CachingHTableFactory, and for 4.x-HBase-0.98,
we should either get rid of it (if it's not too much of a perf hit) or at least make it threadsafe.



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