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From "Nicolas Liochon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10018) Change the location prefetch
Date Mon, 25 Nov 2013 11:08:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13831365#comment-13831365
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Nicolas Liochon commented on HBASE-10018:
-----------------------------------------

bq. Does the prefetch have to be done inline
Not really. It's just a little bit more complicated if we start a thread.

bq.  What to do though if 1M regions
It does not care: it reads the next 10 regions, whatever the table size. 
Ihmo, when you have a lot of region it does not really work, when you have just a few it's
not really necessary.
Excepted in the scenario mentioned by Elliott above.

bq.  Could just flip the configuration to turn off prefetch in 0.98? 
I would prefer to be more radical: just remove it. Or at least, make it optional, deactivated
by default, on .96 and .98.
Thinking more about it, that's my prefered scenario. If nobody disagrees, I will do that:
"make it optional, deactivated by default, on .96 and .98."

> Change the location prefetch
> ----------------------------
>
>                 Key: HBASE-10018
>                 URL: https://issues.apache.org/jira/browse/HBASE-10018
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.98.0, 0.96.0
>            Reporter: Nicolas Liochon
>            Assignee: Nicolas Liochon
>            Priority: Minor
>             Fix For: 0.98.0, 0.96.1
>
>
> Issues with prefetching are:
> - we do two calls to meta: one for the exact row, one for the prefetch 
> - it's done in a lock
> - we take the next 10 regions. Why 10, why the 10 next?
> - is it useful if the table has 100K regions?
> Options are:
> - just remove it
> - replace it with a reverse scan: this would save a call
>  



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