[
https://issues.apache.org/jira/browse/CASSANDRA-6106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13779600#comment-13779600
]
Christopher Smith commented on CASSANDRA-6106:
----------------------------------------------
Jonathan:
If you look at my patch, it calibrates against currentTimeMillis() so that you
do get about as proper a "microseconds since the epoch" as is possible. The one
thing you could do to improve it would be to periodically recalibrate with
currentTimeMillis, but I'd argue that is actually a *bad* thing, as that would
introduce the possibility of timestamps that go back in time.
What this does is dramatically reduce the probability that two concurrent
writes sent to two different nodes will collide (and therefore Cassandra
violates its atomicity "guarantee").
> 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: Bug
> Components: Core
> Environment: DSE Cassandra 3.1, but also HEAD
> Reporter: Christopher Smith
> Priority: Minor
> Labels: collision, conflict, timestamp
> Attachments: microtimstamp.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().
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
