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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13389) [REGRESSION] HBASE-12600 undoes skip-mvcc parse optimizations
Date Tue, 07 Apr 2015 00:14:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14482262#comment-14482262
] 

Lars Hofhansl commented on HBASE-13389:
---------------------------------------

Yeah, not related to log roll, sorry. I meant the max time before we force a memstore flush
(1 hour by default)... HBASE-5930.

I still have not heard a convincing reason why the time to keep the mvcc stuff around needs
to be greater than an hour or two :)


> [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
>         Attachments: 13389.txt
>
>
> 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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