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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6506) Setting CACHE_BLOCKS to false in an hbase shell scan doesn't work
Date Sun, 05 Aug 2012 16:05:02 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13428866#comment-13428866
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stack commented on HBASE-6506:
------------------------------

Can you make a patch Josh?  Thanks.

You probably don't want to turn off caching completely?  You should cache at least the blocks
that hold the hfile indices.  Otherwise, if caching fully off, any read will have to bring
in the indices each time first.
                
> Setting CACHE_BLOCKS to false in an hbase shell scan doesn't work
> -----------------------------------------------------------------
>
>                 Key: HBASE-6506
>                 URL: https://issues.apache.org/jira/browse/HBASE-6506
>             Project: HBase
>          Issue Type: Bug
>          Components: shell
>    Affects Versions: 0.94.0
>            Reporter: Josh Wymer
>            Priority: Minor
>              Labels: cache, ruby, scan, shell
>   Original Estimate: 1m
>  Remaining Estimate: 1m
>
> I was attempting to prevent blocks from being cached by setting CACHE_BLOCKS => false
in the hbase shell when doing a scan but I kept seeing tons of evictions when I ran it. After
inspecting "table.rb" I found this line:
> cache = args["CACHE_BLOCKS"] || true
> The problem then is that if CACHE_BLOCKS is false then this expression will always return
true. Therefore, it's impossible to turn off block caching. 

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