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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12411) Avoid seek + read completely?
Date Sun, 09 Nov 2014 19:23:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14204071#comment-14204071
] 

Lars Hofhansl commented on HBASE-12411:
---------------------------------------

Unfortunately the numbers of very inconclusive. Of course I can set it up such that pread
is better, but if the scans are just slightly better scattered across HFiles then the prefetching
show benefit, at least for larger scans.

It almost seems that Scan needs another option in addition to small scans, an option to force
pread. Meh. I'll investigate some more.


> 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
>
> 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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