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https://issues.apache.org/jira/browse/HBASE-15158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15132679#comment-15132679
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stack commented on HBASE-15158:
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bq. Is it possible to double release a row lock in the finally clause when
there's an exception in the Coprocessor? Does that matter ?
Where could we double unlock? Where you looking? A double unlock would be bad
I'd say. We could unlock someone else. If we double-complete the mvcc, it
explodes... Maybe that is our canary? Maybe I should change this row locking
key to be the row byte array identity or something, something that is unique to
the particular instance.
> Change order in which we do write pipeline operations; do all under row locks!
> ------------------------------------------------------------------------------
>
> Key: HBASE-15158
> URL: https://issues.apache.org/jira/browse/HBASE-15158
> Project: HBase
> Issue Type: Sub-task
> Components: Performance
> Reporter: stack
> Assignee: stack
> Fix For: 2.0.0
>
> Attachments: 15158.patch, 15158v2.patch, 15158v3.patch,
> 15158v4.patch, 15158v4.patch
>
>
> Change how we do our write pipeline. I want to do all write pipeline ops
> under row lock so I lean on this fact fixing performance regression in
> check-and-set type operations like increment, append, and checkAnd* (see
> sibling issue HBASE-15082).
> To be specific, we write like this now:
> {code}
> # take rowlock
> # start mvcc
> # append to WAL
> # add to memstore
> # let go of rowlock
> # sync WAL
> # in case of error: rollback memstore
> {code}
> Instead, write like this:
> {code}
> # take rowlock
> # start mvcc
> # append to WAL
> # sync WAL
> # add to memstore
> # let go of rowlock
> ... no need to do rollback.
> {code}
> The old ordering was put in place because it got better performance in a time
> when WAL was different and before row locks were read/write (HBASE-12751).
> Testing in branch-1 shows that a reordering and skipping mvcc waits gets us
> back to the performance we had before we unified mvcc and sequenceid
> (HBASE-8763). Tests in HBASE-15046 show that at the macro level using our
> usual perf tools, reordering pipeline seems to cause no slowdown (see
> HBASE-15046). A rough compare of increments with reordered write pipeline
> seems to have us getting back a bunch of our performance (see tail of
> https://issues.apache.org/jira/browse/HBASE-15082?focusedCommentId=15111703&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15111703
> and subsequent comment).
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