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Sylvain Lebresne commented on CASSANDRA-1954: --------------------------------------------- Correct me if I am wrong but I think there is a 2 things: * We need to ensure that we call the discard of the commmit context post-flush in the same order that we got the context pre-flush. A lock is fine, especially if we diminish contention on it with double-checking or with an atomic boolean. That this block all writes however seems unnecessary. Why lock the read-lock during write (for that purpose I mean)? As long as we get the commit log context and schedule the post-flush task before changing the active memtable, we should be right. We may have to replay a tiny bit more, since a few write will go into the being flushed memtable after we got the context, but we won't lose any. On a related note, why I understand why we want to preserve this 'pre-flush/post-flush' order er column family, I'm not sure I understand why it must be global since the commit log header distinguishes between the different CFs ? * We need to keep writes out of being-flushed memtables. For that, we can use per-memtable counters and make flush start by waiting on the counter to reach 0. Am I missing something obvious here ? As for the View structure proposed by Stu in the previous comment, this could actually be a quite reasonable solution for CASSANDRA-2105 so I'll probably give that a shot too in this context. > 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 > Priority: Minor > Attachments: > 0001-Double-check-in-maybeSwitchMemtable-to-minimize-writeL.txt > > > {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