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From: Jonathan Ellis <jbellis@gmail.com>
Date: Fri, 19 Aug 2011 21:38:47 -0500
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 <CALdd-zhpYG12XQkt8okSegvcqaK0QzUBYA1ZLdJZa9tV2JRKBQ@mail.gmail.com>
Subject: Re: memory overhead of vector clocks vs timestamps and running
 *without* either to save memory?
To: user@cassandra.apache.org
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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/v=
ersioning/VectorClock.java

On Fri, Aug 19, 2011 at 7:41 PM, Kevin Burton <burton@spinn3r.com> wrote:
> I have a few questions which I can't seem to find answers to...
> I know that the memory overhead of timestamps is 8 bytes per row/column.
> =A0=A0What is the memory overhead of vector clocks?
> Is it possible (at least in theory) to run without timestamps on your
> values? =A0I'm fine with last writer wins semantics and the memory overhe=
ad
> here seems very high.
> I understand that the timestamps might also be for repartitioning which a=
dds
> complexity.
> Thanks!
>
> --
>
> Founder/CEO=A0Spinn3r.com
>
> Location:=A0San Francisco, CA
> Skype:=A0burtonator
>
> Skype-in:=A0(415) 871-0687
>


--=20
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com