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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: What does a write lock ?
Date Thu, 07 Jul 2011 18:24:45 GMT
Hi Jonnathan,

This brings up an important question.  I have been assuming that the
validation check is part of the atomic update operation. Is this NOT the
case?  Which is to say, can the row be changed between the time the
validation method is executed and the validated data is written?

The reason I ask is because I have been thinking of this as effectively a
write-lock on the row during the entire update
process, including validation, but your answer has caused some concerns that
this is wrong...

Thanks

JK

On Thu, Jul 7, 2011 at 2:01 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> None of the above, it uses a glorified CAS* at the column level
>
> *http://en.wikipedia.org/wiki/Compare-and-swap
>
> On Thu, Jul 7, 2011 at 12:51 PM, A J <s5alye@gmail.com> wrote:
> > Does a write lock:
> > 1. Just the columns in question for the specific row in question ?
> > 2. The full row in question ?
> > 3. The full CF ?
> >
> > I doubt read does any locks.
> >
> > Thanks.
> >
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of DataStax, the source for professional Cassandra support
> http://www.datastax.com
>



-- 
It's always darkest just before you are eaten by a grue.

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