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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8362) Possible MultiGet optimization
Date Wed, 17 Apr 2013 22:43:18 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8362?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13634546#comment-13634546
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Lars Hofhansl commented on HBASE-8362:
--------------------------------------

Doing this via a custom filter is possible. Currently, though, you cannot have different filters
in different regions (i.e. all Gets would have to be passed to every filter materialized in
every region); at least I do not see a way to do that.

The problem with reseek is that it does not necessarily seek to an existing row. Say you have
row1 and row3 in a table and now you issue a get for row2. You'd reseek to row2, which would
place the scanner just before row3, the next call to next() would return row3, which is not
what you want; hence we'd either have know whether the reseek found an existing row (in which
case next will return the one we want) or we need to check the result from next() (and if
the row key does not match we are this work for nothing).

The other question is around bloom filters, which currently are only checked for get scans.

                
> Possible MultiGet optimization
> ------------------------------
>
>                 Key: HBASE-8362
>                 URL: https://issues.apache.org/jira/browse/HBASE-8362
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>
> Currently MultiGets are executed on a RegionServer in a single thread in a loop that
handles each Get separately (opening a scanner, seeking, etc).
> It seems we could optimize this (per region at least) by opening a single scanner and
issue a reseek for each Get that was requested.
> I have not tested this yet and no patch, but I would like to solicit feedback on this
idea.

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