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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12411) Avoid seek + read completely?
Date Tue, 18 Nov 2014 05:28:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14215729#comment-14215729
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ramkrishna.s.vasudevan commented on HBASE-12411:
------------------------------------------------

Patch looks great.  This ensures that the readers of compaction do not interfere with user
reads.  As Stack's comments says we may end up in opening more streams in the NN on the same
HDFS blocks. (May be am wrong as how HDFS would handle it).
But this patch would ensure that the on going compaction would not affect the user scans by
sharing the same reader.

> Avoid seek + read completely?
> -----------------------------
>
>                 Key: HBASE-12411
>                 URL: https://issues.apache.org/jira/browse/HBASE-12411
>             Project: HBase
>          Issue Type: Brainstorming
>          Components: Performance
>            Reporter: Lars Hofhansl
>         Attachments: 12411-v2.txt, 12411-v3.txt, 12411.txt
>
>
> In the light of HDFS-6735 we might want to consider refraining from seek + read completely
and only perform preads.
> For example currently a compaction can lock out every other scanner over the file which
the compaction is currently reading for compaction.
> At the very least we can introduce an option to avoid seek + read, so we can allow testing
this in various scenarios.
> This will definitely be of great importance for projects like Phoenix which parallelize
queries intra region (and hence readers will used concurrently by multiple scanner with high
likelihood.)



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