The simple thing to say is: If you send a batch_mutate the order which the rows are written is undefined. So you should not make any assumptions such as if rows C is stored, rows A and B also have.
They may do but AFAIK it is not part of the API contract. For the thrift API batch_mutate takes a Map of mutations keyed on the row key. CQL builds a list of row mutations in the same order as the statement. Even if they are in a list there is no guarantee they will be processed in that order. If you get a timed out error all you know is the mutation, as a whole, was applied of < CL nodes. Cheers ----------------- Aaron Morton Freelance Developer @aaronmorton http://www.thelastpickle.com On 15/03/2012, at 1:22 PM, Tyler Hobbs wrote: > Ah, my mistake, you are correct. Not sure why I had forgotten that. > > The pycassa docs are slightly wrong there, though. It's technically atomic > for the same key across multiple column families. I'll get that fixed. > > On Wed, Mar 14, 2012 at 5:22 PM, A J <s5a...@gmail.com> wrote: > > No, batch_mutate() is an atomic operation. When a node locally applies a > > batch mutation, either all of the changes are applied or none of them are.< > The steps in my batch are not confined to a single CF, nor to a single key. > > The documentation says: > datastax: > Column updates are only considered atomic within a given record (row). > > Pycassa.batch: > This interface does not implement atomic operations across column > families. All the limitations of the batch_mutate Thrift API call > applies. Remember, a mutation in Cassandra is always atomic per key > per column family only. > > > On Wed, Mar 14, 2012 at 4:15 PM, Tyler Hobbs <ty...@datastax.com> wrote: > > On Wed, Mar 14, 2012 at 11:50 AM, A J <s5a...@gmail.com> wrote: > >> > >> > >> Are you saying the way 'batch mutate' is coded, the order of writes in > >> the batch does not mean anything ? You can ask the batch to do A,B,C > >> and then D in sequence; but sometimes Cassandra can end up applying > >> just C and A,B (and D) may still not be applied ? > > > > > > No, batch_mutate() is an atomic operation. When a node locally applies a > > batch mutation, either all of the changes are applied or none of them are. > > > > Aaron was referring to the possibility that one of the replicas received the > > batch_mutate, but the other replicas did not. > > > > -- > > Tyler Hobbs > > DataStax > > > > > > -- > Tyler Hobbs > DataStax >
