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From Jonathan Ellis <>
Subject Re: Achieving isolation on single row modifications with batch_mutate
Date Tue, 30 Nov 2010 14:50:51 GMT
On Sat, Nov 27, 2010 at 10:12 AM, E S <> wrote:
> I'm trying to figure out the best way to achieve single row modification
> isolation for readers.

I have a lot of No's for you. :)

> As an example, I have 2 rows (1,2) with 2 columns (a,b).  If I modify both rows,
> I don't care if the user sees the write operations completed on 1 and not on 2
> for a short time period (seconds).  I also don't care if when reading row 1 the
> user gets the new value, and then on a re-read gets the old value (within a few
> seconds).  Because of this, I have been planning on using a consistency level of
> one.
> However, if I modify both columns A,B on a single row, I need both changes on
> the row to be visible/invisible atomically.  It doesn't matter if they both
> become visible and then both invisible as the data propagates across nodes, but
> a half-completed state on an initial read will basically be returning corrupt
> data given my apps consistency requirements.  My understanding from the FAQ that
> this single row multicolumn change provides no read isolation, so I will have
> this problem.  Is this correct?  If so:
> Question 1:  Is there a way to get this type of isolation without using a
> distributed locking mechanism like cages?


> Question 2:  Are there any plans to implement this type of isolation within
> Cassandra?


> Question 3:  If I went with a distributed locking mechanism, what consistency
> level would I need to use with Cassandra?  Could I still get away with a
> consistency level of one?

Maybe.  If you want to guarantee that you see the most recent write,
then ONE will not be high enough. But if all you care about is seeing
all of the update or none of it, then ONE + locking will be fine.

> Question 4:  Does anyone know of a good c# alternative to cages/zookeeper?


Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support

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