[
https://issues.apache.org/jira/browse/HBASE-13389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14509175#comment-14509175
]
stack commented on HBASE-13389:
-------------------------------
bq. After 6 days (currently) we are zero'ing mvcc during compactions.
[~lhofhansl] Pardon me, where is this enforced (all hfiles participating in a
compaction must be 6-days old?) 6-days is arbitrary, right? It means that
there cannot be a WAL outstanding that has an edit that has not yet been
flushed, right? It also means, that there cannot be an edit in a WAL that has
not been replicated and flushed on the remote side? Is there a trigger we could
use instead rather than an arbitrary timing?
[~jeffreyz] Thanks for chiming in. I don't see the WALEdit sequenceid being
used when we replicate. Is this something to implement? (Sounds like a good
idea... )
> [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
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
