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From "Mikhail Bautin (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4465) Lazy-seek optimization for StoreFile scanners
Date Wed, 05 Oct 2011 21:32:29 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13121497#comment-13121497

Mikhail Bautin commented on HBASE-4465:

Thanks, Jonathan! I just chatted with Nicolas and he said we should not worry about the 89
branch yet because he will be syncing our internal changes into the public 89 branch.
> Lazy-seek optimization for StoreFile scanners
> ---------------------------------------------
>                 Key: HBASE-4465
>                 URL: https://issues.apache.org/jira/browse/HBASE-4465
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Mikhail Bautin
>            Assignee: Mikhail Bautin
>              Labels: optimization, seek
>             Fix For: 0.89.20100924, 0.94.0
>         Attachments: HBASE-4465_Lazy-seek_optimization_for_St-20111005121052-b2ea8753.patch
> Previously, if we had several StoreFiles for a column family in a region, we would seek
in each of them and only then merge the results, even though the row/column we are looking
for might only be in the most recent (and the smallest) file. Now we prioritize our reads
from those files so that we check the most recent file first. This is done by doing a "lazy
seek" which pretends that the next value in the StoreFile is (seekRow, seekColumn, lastTimestampInStoreFile),
which is earlier in the KV order than anything that might actually occur in the file. So if
we don't find the result in earlier files, that fake KV will bubble up to the top of the KV
heap and a real seek will be done. This is expected to significantly reduce the amount of
disk IO (as of 09/22/2011 we are doing dark launch testing and measurement).
> This is joint work with Liyin Tang -- huge thanks to him for many helpful discussions
on this and the idea of putting fake KVs with the highest timestamp of the StoreFile in the
scanner priority queue.

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