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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:
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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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