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From "Liyin Tang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7266) [89-fb] Using pread for non-compaction read request
Date Wed, 31 Jul 2013 17:19:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13725443#comment-13725443

Liyin Tang commented on HBASE-7266:

Chao,we have switched all the read operation to pread in the 89-fb branch. There are 2 followup
tasks for the pread. 1) The DFSClient maintains a connection pool instead of creating new
connection for each pread operation. 2) HBase will actively pre-load the next several blocks
in a stream fashion for large sequential scans (HBASE-9102)
> [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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