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https://issues.apache.org/jira/browse/CASSANDRA-14292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16388039#comment-16388039
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ZhaoYang commented on CASSANDRA-14292:
--------------------------------------

It’s 3.0.16 only..

> Batch commitlog performance regression in 3.0.16
> ------------------------------------------------
>
>                 Key: CASSANDRA-14292
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14292
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: ZhaoYang
>            Assignee: ZhaoYang
>            Priority: Major
>             Fix For: 3.0.x
>
>
> Prior to CASSANDRA-13987, in batch commitlog mode, commitlog will be synced 
> to disk right after mutation comes.
>  * haveWork semaphore is released in BatchCommitLogService.maybeWaitForSync
>  * AbstractCommitlogService will continue and sync to disk
> After C-13987, it makes a branch for chain maker flush more frequently in 
> periodic mode. To make sure in batch mode CL still flushes immediately, it 
> added {{syncRequested}} flag.
>  Unfortunately, in 3.0 branch, this flag is not being set to true when 
> mutation is waiting.
> So in AbstractCommitlogService, it will not execute the CL sync branch until 
> it reaches sync window(2ms)..
> {code:java|title=AbstractCommitLogService.java}
> if (lastSyncedAt + syncIntervalMillis <= pollStarted || shutdown || 
> syncRequested)
> {
>     // in this branch, we want to flush the commit log to disk
>     syncRequested = false;
>     commitLog.sync(shutdown, true);
>     lastSyncedAt = pollStarted;
>     syncComplete.signalAll();
> }
> else
> {
>     // in this branch, just update the commit log sync headers
>     commitLog.sync(false, false);
> }
> {code}



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