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Posted to commits@cassandra.apache.org by "Christopher Smith (JIRA)" <ji...@apache.org> on 2013/12/21 10:16:15 UTC
[jira] [Commented] (CASSANDRA-6106) QueryState.getTimestamp() &
FBUtilities.timestampMicros() reads current timestamp with
System.currentTimeMillis() * 1000 instead of System.nanoTime() / 1000
[ https://issues.apache.org/jira/browse/CASSANDRA-6106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13854825#comment-13854825 ]
Christopher Smith commented on CASSANDRA-6106:
----------------------------------------------
If we really care about performance for getting the time, on linux we should just create an NIO buffer around the real-time timer and avoid calling out to C to get the time completely.
> QueryState.getTimestamp() & FBUtilities.timestampMicros() reads current timestamp with System.currentTimeMillis() * 1000 instead of System.nanoTime() / 1000
> ------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-6106
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6106
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Environment: DSE Cassandra 3.1, but also HEAD
> Reporter: Christopher Smith
> Priority: Minor
> Labels: timestamps
> Fix For: 2.1
>
> Attachments: microtimstamp.patch, microtimstamp_random.patch, microtimstamp_random_rev2.patch
>
>
> I noticed this blog post: http://aphyr.com/posts/294-call-me-maybe-cassandra mentioned issues with millisecond rounding in timestamps and was able to reproduce the issue. If I specify a timestamp in a mutating query, I get microsecond precision, but if I don't, I get timestamps rounded to the nearest millisecond, at least for my first query on a given connection, which substantially increases the possibilities of collision.
> I believe I found the offending code, though I am by no means sure this is comprehensive. I think we probably need a fairly comprehensive replacement of all uses of System.currentTimeMillis() with System.nanoTime().
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