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Josh Elser commented on ACCUMULO-2766: -------------------------------------- [~kturner] how's progress on this coming along? Given what you describe here, I think this would be a good candidate to get in before a 1.5.2. Do you have an estimate on time remaining? > Single walog operation may wait for multiple hsync calls > -------------------------------------------------------- > > Key: ACCUMULO-2766 > URL: https://issues.apache.org/jira/browse/ACCUMULO-2766 > Project: Accumulo > Issue Type: Bug > Components: tserver > Affects Versions: 1.5.0, 1.5.1, 1.6.0 > Reporter: Keith Turner > Assignee: Keith Turner > Priority: Critical > Labels: performance > Fix For: 1.5.2, 1.6.1 > > Attachments: ACCUMULO-2677-1.patch, ACCUMULO-2766-2.patch > > > While looking into slow {{hsync}} calls, I noticed an oddity in the way > Accumulo processes syncs. Specifically the way {{closeLock}} is used in > {{DfsLogger}}, it seems like the following situation could occur. > > # thread B starts executing DfsLogger.LogSyncingTask.run() > # thread 1 enters DfsLogger.logFileData() > # thread 1 writes to walog > # thread 1 locks _closeLock_ > # thread 1 adds sync work to workQueue > # thread 1 unlocks _closeLock_ > # thread B takes sync work off of workQueue > # thread B locks _closeLock_ > # thread B calls sync > # thread 3 enters DfsLogger.logFileData() > # thread 3 writes to walog > # thread 3 blocks locking _closeLock_ > # thread 4 enters DfsLogger.logFileData() > # thread 4 writes to walog > # thread 4 blocks locking _closeLock_ > # thread B unlocks _closeLock_ > # thread 4 locks _closeLock_ > # thread 4 adds sync work to workQueue > # thread B takes sync work off of workQueue > # thread B blocks locking _closeLock_ > # thread 4 unlocks _closeLock_ > # thread B locks _closeLock_ > # thread B calls sync > # thread B unlocks _closeLock_ > # thread 3 locks _closeLock_ > # thread 3 adds sync work to workQueue > # thread 3 unlocks _closeLock_ > In this situation thread 3 unnecessarily has to wait for an extra {{hsync}} > call. Not sure if this situation actually occurs, or if it occurs very > frequently. Looking at the code it seems like it would be nice if sync > operations could be queued w/o synchronizing w/ sync operations. -- This message was sent by Atlassian JIRA (v6.2#6252)