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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1823) Ability for Scanners to bypass the block cache
Date Fri, 11 Sep 2009 03:38:57 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1823?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753969#action_12753969
] 

Jonathan Gray commented on HBASE-1823:
--------------------------------------

Thanks for review, Andrew.

Opened HBASE-1827 to add option to shell.  Don't want to hold up commit of this.

Seems to work in preliminary testing.  Going to do more testing tomorrow and then will commit.


> Ability for Scanners to bypass the block cache
> ----------------------------------------------
>
>                 Key: HBASE-1823
>                 URL: https://issues.apache.org/jira/browse/HBASE-1823
>             Project: Hadoop HBase
>          Issue Type: New Feature
>          Components: client, regionserver
>    Affects Versions: 0.20.0
>            Reporter: Jonathan Gray
>            Assignee: Jonathan Gray
>             Fix For: 0.20.1, 0.21.0
>
>         Attachments: HBASE-1823-v1.patch, HBASE-1823-v2.patch
>
>
> There are a number of use cases where exposing the ability to not cache blocks during
a scan would be valuable.  For example, running row counts.
> The LRU is scan-resistant, so it does provide some protection already, but even in that
case all you prevent is the eviction of hot blocks.  The LRU still runs many evictions and
the blocks are referenced for much longer periods of time, so this adds enormous stress to
the GC.
> Compactions already do this.  This issue is about exposing that as a switch to the client-side
Scan object (will also enable it for MR jobs then).

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