[jira] [Commented] (HBASE-13389) [REGRESSION] HBASE-12600 undoes skip-mvcc parse optimizations

["Jeffrey Zhong (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-13389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14394111#comment-14394111 ] 

Jeffrey Zhong commented on HBASE-13389:
---------------------------------------

[~stack] The performance regression is due to we keep mvcc values longer(HBASE-11315) so comes the later change https://github.com/apache/hbase/commit/2c280e62530777ee43e6148fd6fcf6dac62881c0#diff-07c7ac0a9179cedff02112489a20157fR96. 

I'm surprised the extra mvcc value caused so much perf regression. Here is the code which calculates minSeqId to keep in file Compactor.java during compaction. 

{code}
        // when isAllFiles is true, all files are compacted so we can calculate the smallest 
        // MVCC value to keep
        if(fd.minSeqIdToKeep < file.getMaxMemstoreTS()) {
          fd.minSeqIdToKeep = file.getMaxMemstoreTS();
        }
....
        // output to writer:
        for (Cell c : cells) {
          if (cleanSeqId && c.getSequenceId() <= smallestReadPoint) {
            CellUtil.setSequenceId(c, 0);
          }
{code}

> [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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