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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8001) Avoid unnecessary lazy seek
Date Fri, 08 Mar 2013 06:20:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13596868#comment-13596868
] 

Lars Hofhansl commented on HBASE-8001:
--------------------------------------

In my scenario I can not measure an improvement:
* all data in the blockcache
* 40m small KVs (8 byte keys, 20 byte values) across two CFs
* scan + filter where filter filters everything at the server
* column family with a single column
* VERSIONS=1
* table is fully compacted

Tests:
* adding a single family to Scan object: 11.8
* adding the family+column to the Scan object: 13.1

I get the same numbers with or without the patch. The 2nd number should have improved.

                
> Avoid unnecessary lazy seek
> ---------------------------
>
>                 Key: HBASE-8001
>                 URL: https://issues.apache.org/jira/browse/HBASE-8001
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>    Affects Versions: 0.94.5
>            Reporter: Raymond Liu
>            Assignee: Raymond Liu
>             Fix For: 0.98.0
>
>         Attachments: HBASE-8001_onescanner.patch
>
>
> Lazy seek helps to reduce the real seek needed for multi hfile, when the kv from newer
hfile is enough to satisfy the query.
> While in many case, it just push the real seek later, and do not reduce the number of
real seek. e.g. there are only one hfile, or storefilescanner is closed and only one left,
or the scan need to go through all the versions, or there are only one version of row and
a sequence scan is performed. In these case, lazy seek just bring extra overhead.

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