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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. -- This message is automatically generated by JIRA. For more information on JIRA, see: http://www.atlassian.com/software/jira