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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 21:30:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14179145#comment-14179145
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Lars Hofhansl commented on HBASE-12311:
---------------------------------------

It's not hard to record that information per block. It's hard to get that information out
to where/when I need it.

In the SQM I want to know how many versions (and columns actually) I can expect worst case.
If it's maintained per block that has to be aggregated somewhere. If it is per store file
it is easily aggregated per store.


> 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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