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https://issues.apache.org/jira/browse/CASSANDRA-1954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13010750#comment-13010750
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Sylvain Lebresne commented on CASSANDRA-1954:
---------------------------------------------
The main advantages in my opinion is that write don't have to acquire the flush
read lock anymore. This means that you avoid the stop-the-world behavior each
time a memtable is switched. The idea of the volatile boolean for writes is
that it will be set only if while scheduling a flush we detect a over capacity
problem. This may not be less code that we had before, but I do believe this
will help getting much uniform latencies for writes.
> Double-check or replace RRW memtable lock
> -----------------------------------------
>
> Key: CASSANDRA-1954
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1954
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Stu Hood
> Assignee: Sylvain Lebresne
> Priority: Minor
> Fix For: 0.8
>
> Attachments:
> 0001-Double-check-in-maybeSwitchMemtable-to-minimize-writeL.txt,
> 0001-Remove-flusherLock-readLock.patch, 1954-0.7-v2.txt, 1954-v2.txt,
> 1954_trunk.patch
>
> Original Estimate: 8h
> Remaining Estimate: 8h
>
> {quote}...when a Memtable reaches its threshold, up to (all) N write threads
> will often notice, and race to acquire the writeLock in order to freeze the
> memtable. This means that we do way more writeLock acquisitions than we need
> to...{quote}
> See CASSANDRA-1930 for backstory, but adding double checking inside a read
> lock before trying to re-entrantly acquire the writelock would eliminate most
> of these excess writelock acquisitions.
> Alternatively, we should explore removing locking from these structures
> entirely, and replacing the writeLock acquisition with a per-memtable counter
> of active threads.
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