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Date: Fri, 27 Sep 2013 14:32:02 +0000 (UTC)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12670852.1380237933608.30316.1380292322745@arcas>
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Subject: [jira] [Commented] (CASSANDRA-6106) QueryState.getTimestamp() &
 FBUtilities.timestampMicros() reads current timestamp with
 System.currentTimeMillis() * 1000 instead of System.nanoTime() / 1000
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    [ https://issues.apache.org/jira/browse/CASSANDRA-6106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13779983#comment-13779983 ] 

Jonathan Ellis commented on CASSANDRA-6106:
-------------------------------------------

I like it.

I'd be inclined to prefer reserving a couple bytes from our existing 64bit clock, noting that we have several centuries of headroom in micros-since-epoch in 48 bits.  Compression will help on disk, but we do have to decompress to do anything useful and I don't want to cause more GC on every op to deal with what is a pretty rare corner case.
                
> 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().

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