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https://issues.apache.org/jira/browse/HBASE-13389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14395851#comment-14395851
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Lars Hofhansl commented on HBASE-13389:
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[~jeffreyz], [~stack], I have to admit I do not quite follow the reasoning
behind HBASE-12600.
The main question I have:
Do we need valid (non 0) mvcc readpoints for committed data (i.e. data that was
flushed to an HFile and hence we'll never need to replay any HLogs for those)?
Do we need these anywhere but in the memstore?
> [REGRESSION] HBASE-12600 undoes skip-mvcc parse optimizations
> -------------------------------------------------------------
>
> Key: HBASE-13389
> URL: https://issues.apache.org/jira/browse/HBASE-13389
> Project: HBase
> Issue Type: Sub-task
> Components: Performance
> Reporter: stack
>
> HBASE-12600 moved the edit sequenceid from tags to instead exploit the
> mvcc/sequenceid slot in a key. Now Cells near-always have an associated
> mvcc/sequenceid where previous it was rare or the mvcc was kept up at the
> file level. This is sort of how it should be many of us would argue but as a
> side-effect of this change, read-time optimizations that helped speed scans
> were undone by this change.
> In this issue, lets see if we can get the optimizations back -- or just
> remove the optimizations altogether.
> The parse of mvcc/sequenceid is expensive. It was noticed over in HBASE-13291.
> The optimizations undone by this changes are (to quote the optimizer himself,
> Mr [~lhofhansl]):
> {quote}
> Looks like this undoes all of HBASE-9751, HBASE-8151, and HBASE-8166.
> We're always storing the mvcc readpoints, and we never compare them against
> the actual smallestReadpoint, and hence we're always performing all the
> checks, tests, and comparisons that these jiras removed in addition to
> actually storing the data - which with up to 8 bytes per Cell is not trivial.
> {quote}
> This is the 'breaking' change:
> https://github.com/apache/hbase/commit/2c280e62530777ee43e6148fd6fcf6dac62881c0#diff-07c7ac0a9179cedff02112489a20157fR96
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