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From Ryan King <r...@twitter.com>
Subject Re: Memory overhead of vector clocks…. how often are they pruned?
Date Wed, 24 Aug 2011 16:05:54 GMT
On Tue, Aug 23, 2011 at 7:58 PM, Kevin Burton <burton@spinn3r.com> wrote:

> I had a thread going the other day about vector clock memory usage and that
> it is a series of (clock id, clock):ts and the ability to prune old entries
> … I'm specifically curious here how often old entries are pruned.
>
> If you're storing small columns within cassandra.  Say just an integer.
>  The vector clock overhead could easily use up far more data than is
> actually in your database.
>
> However, if they are pruned, then this shouldn't really be a problem.
>
> How much memory is this wasting?
>

I think there is some confusion here– cassandra doesn't use vector clocks.

-ryan


> Thoughts?
>
>
>     Jonathan Ellis jbellis@gmail.com to user
>  show details Aug 19 (4 days ago)
>  The problem with naive last write wins is that writes don't always
> arrive at each replica in the same order.  So no, that's a
> non-starter.
>
> Vector clocks are a series of (client id, clock) entries, and usually
> a timestamp so you can prune old entries.  Obviously implementations
> can vary, but to pick a specific example, Voldemort [1] uses 2 bytes
> per client id, a variable number (at least one) of bytes for the
> clock, and 8 bytes for the timestamp.
>
> [1]
> https://github.com/voldemort/voldemort/blob/master/src/java/voldemort/versioning/VectorClock.java
>
>
> --
>
> Founder/CEO Spinn3r.com
>
> Location: *San Francisco, CA*
> Skype: *burtonator*
>
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