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Posted to issues@hbase.apache.org by "Chao Shi (JIRA)" <ji...@apache.org> on 2013/08/01 10:13:52 UTC

[jira] [Commented] (HBASE-7266) [89-fb] Using pread for non-compaction read request

    [ https://issues.apache.org/jira/browse/HBASE-7266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13726207#comment-13726207 ] 

Chao Shi commented on HBASE-7266:
---------------------------------

Lars, yes, we're using an early 0.94 version. Thanks for the fix and we will try to benchmark a newer version. I think the fix is too tricky and I would prefer the idea Liyin proposed. Let's discus in the new issue.
                
> [89-fb] Using pread for non-compaction read request
> ---------------------------------------------------
>
>                 Key: HBASE-7266
>                 URL: https://issues.apache.org/jira/browse/HBASE-7266
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Liyin Tang
>
> There are 2 kinds of read operations in HBase: pread and seek+read.
> Pread, positional read, is stateless and create a new connection between the DFSClient and DataNode for each operation. While seek+read is to seek to a specific postion and prefetch blocks from data nodes. The benefit of seek+read is that it will cache the prefetch result but the downside is it is stateful and needs to synchronized.
> So far, both compaction and scan are using seek+read, which caused some resource contention. So using the pread for the scan request can avoid the resource contention. In addition, the region server is able to do the prefetch for the scan request (HBASE-6874) so that it won't be necessary to let the DFSClient to prefetch the data any more.
> I will run through the scan benchmark (with no block cache) with verify the performance.

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