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From "Jason Rutherglen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4027) Enable direct byte buffers LruBlockCache
Date Fri, 24 Jun 2011 23:10:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054737#comment-13054737
] 

Jason Rutherglen commented on HBASE-4027:
-----------------------------------------

{quote}One big question is whether you're going to make copies out of the direct byte buffers
on each read of that block, or if you're going to change KeyValue to use the ByteBuffer interface
(or some other) instead of the byte[] directly{quote}

Right the {{HFile.Scanner.getKeyValue()}} method is calling {{block.array()}}.  We'd need
to track down all {{byte[]}} references, and convert them to {{ByteBuffer}}.  That's more
of a separate Jira.  

I think converting a direct ByteBuffer to byte[] will generate a fair amount of garbage, though
of a different (smaller and more numerous) kind than the blocks.

> Enable direct byte buffers LruBlockCache
> ----------------------------------------
>
>                 Key: HBASE-4027
>                 URL: https://issues.apache.org/jira/browse/HBASE-4027
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Jason Rutherglen
>            Priority: Minor
>
> Java offers the creation of direct byte buffers which are allocated outside of the heap.
> They need to be manually free'd, which can be accomplished using an documented {{clean}}
method.
> The feature will be optional.  After implementing, we can benchmark for differences in
speed and garbage collection observances.

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