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https://issues.apache.org/jira/browse/HBASE-10247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13969063#comment-13969063
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Lars Hofhansl commented on HBASE-10247:
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That is one use case. I meant an even more general scenario. Currently for
*any* scan we need to seek into all involved HFiles and the memstore to find
the next element.
For many scans (for example when the set of columns is known ahead of time, and
we're looking for latest N versions only) we can seek on-demand in order of the
newest to latest, as soon as we found what we're looking for we can stop and
avoid seeking into the older HFiles.
> Client promises about timestamps
> --------------------------------
>
> Key: HBASE-10247
> URL: https://issues.apache.org/jira/browse/HBASE-10247
> Project: HBase
> Issue Type: Brainstorming
> Reporter: Lars Hofhansl
> Priority: Minor
>
> This is to start a discussion about timestamp promises declared per table of
> CF.
> For example if a client promises only monotonically increasing timestamps (or
> no custom set timestamps) and VERSIONS=1, we can aggressively and easily
> remove old versions of the same row/fam/col from the memstore before we
> flush, just by supplying a comparator that ignores the timestamp (i.e. two KV
> just differing by TS would be considered equal).
> That would increase the performance of counters significantly.
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