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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-12311) Version stats in HFiles?
Date Fri, 07 Nov 2014 01:43:35 GMT

     [ https://issues.apache.org/jira/browse/HBASE-12311?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Lars Hofhansl updated HBASE-12311:
----------------------------------
    Attachment: 12311-v2.txt

Got another few minutes on this. Bit further now. Still not working at all. Again just want
to park it.
* collects standard deviation as well
* knows how to combine trackers from multiple files - including the standard deviation correctly

The only part left, really, is to hook this up in SQM.

Once I get this working, I'll do some number and see whether this effort is worth it.

> Version stats in HFiles?
> ------------------------
>
>                 Key: HBASE-12311
>                 URL: https://issues.apache.org/jira/browse/HBASE-12311
>             Project: HBase
>          Issue Type: Brainstorming
>            Reporter: Lars Hofhansl
>         Attachments: 12311-v2.txt, 12311.txt, CellStatTracker.java
>
>
> 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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