Question about sharding of rows and atomicity

[Don Smith <ds...@likewise.com>]

Does Cassandra shard the columns of a single row across multiple nodes 
so that to read the columns of the row it may need access to multiple 
nodes?   I'd say "no."   Will a read from a given node ever return 
partial results or is the write to a node of a row atomic?

  Thanks, Don

Re: Question about sharding of rows and atomicity

[Jonathan Ellis <jb...@gmail.com>]

On Wed, Oct 5, 2011 at 1:09 PM, Don Smith <ds...@likewise.com> wrote:
> Does Cassandra shard the columns of a single row across multiple nodes so
> that to read the columns of the row it may need access to multiple nodes?
> I'd say "no."

Correct.

>   Will a read from a given node ever return partial results or
> is the write to a node of a row atomic?

http://wiki.apache.org/cassandra/FAQ#batch_mutate_atomic

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

Re: Question about sharding of rows and atomicity

[Konstantin Naryshkin <ko...@a-bb.net>]

Cassandra does not break apart a row. All of the columns of a row are kept on the same nodes.

I believe that writing multiple columns of the same row is transactional, but not atomic. By which I mean that if one column is written all the other ones will be written as well, but if a read happens while the write is being done it is possible that only some of the columns will have the new values.

----- Original Message -----
From: "Don Smith" <ds...@likewise.com>
To: user@cassandra.apache.org
Sent: Wednesday, October 5, 2011 2:09:36 PM
Subject: Question about sharding of rows and atomicity

Does Cassandra shard the columns of a single row across multiple nodes 
so that to read the columns of the row it may need access to multiple 
nodes?   I'd say "no."   Will a read from a given node ever return 
partial results or is the write to a node of a row atomic?

  Thanks, Don