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https://issues.apache.org/jira/browse/CASSANDRA-14292?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ZhaoYang updated CASSANDRA-14292:
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Attachment: 14292-3.0-unittest.png
14292-3.0-dtest.png
> 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
>
> Attachments: 14292-3.0-dtest.png, 14292-3.0-unittest.png
>
>
> 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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