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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12311) Version stats in HFiles?
Date Tue, 21 Oct 2014 18:00:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14178748#comment-14178748
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Lars Hofhansl commented on HBASE-12311:
---------------------------------------

Are there better/other ideas?
The core issue we want to get to: If a (re)seek would get us to a different HFile block we
should seek, otherwise repeated next()'s inside the block is (far) more efficient. This decision
would need to be made efficient - without needing a bunch of compares of the row-key.

Tracking the maximum number of versions seen would a possible and relatively cheap proxy to
guess the likelihood of a seek getting us out of the current block.


> Version stats in HFiles?
> ------------------------
>
>                 Key: HBASE-12311
>                 URL: https://issues.apache.org/jira/browse/HBASE-12311
>             Project: HBase
>          Issue Type: Brainstorming
>            Reporter: Lars Hofhansl
>
> In HBASE-9778 I basically punted the decision on whether doing repeated scanner.next()
called instead of the issueing (re)seeks to the user.
> I think we can do better.
> One way do that is maintain simple stats of what the maximum number of versions we've
seen for any row/col combination and store these in the HFile's metadata (just like the timerange,
oldest Put, etc).
> Then we estimate fairly accurately whether we have to expect lots of versions (i.e. seek
between columns is better) or not (in which case we'd issue repeated next()'s).



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