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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15158) Change order in which we do write pipeline operations; do all under row locks!
Date Thu, 04 Feb 2016 18:02:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15132679#comment-15132679

stack commented on HBASE-15158:

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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