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https://issues.apache.org/jira/browse/CASSANDRA-6106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13979758#comment-13979758
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Benedict commented on CASSANDRA-6106:
-------------------------------------
Well, what I should have made clear is that I am willing to drop the
monotonicity guarantees, however I am -1 on your extra thread.
But I still think the monotonicity guarantees are good, and not so difficult to
prove, so if we can get somebody who doesn't have a newborn to contend with to
take a look maybe that wouldn't be a bad thing :)
In case it helps, here's a quick proof we can never give a whack value:
{noformat}
1. -100000<= adjustMicros<=100000
2. expire-adjustFrom=1000000000
2a. expireMicros-adjustFromMicros=1000000
3. adjustFromMicros<=micros<=expireMicros
4. delta = (adjustMicros * (micros-adjustFromMicros)) /
(expireMicros-adjustFromMicros)
5. 2a ^ 3 ^ 4 -> expireMicros-adjustFromMicros > micros-adjustFromMicros ->
|delta| <= |adjustMicros|
{noformat}
i.e. the adjustment is definitely always less than adjustMicros, which is
itself always less than 100ms per second (per 1 and 2). So we can never give a
totally whack result. Can do more thorough proofs of other criteria, but I
think this plus my other statement is enough to demonstrate its safety.
> Provide timestamp with true microsecond resolution
> --------------------------------------------------
>
> 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
> Assignee: Benedict
> Priority: Minor
> Labels: timestamps
> Fix For: 2.1 beta2
>
> 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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