Yes, each partition modified by a batch has its modifications applied altogether, atomically (at the node level).
On Friday, 9 September 2016, Bhuvan Rawal <bhu1ra...@gmail.com> wrote: > As per this > <https://docs.datastax.com/en/cql/3.3/cql/cql_reference/batch_r.html> doc > conditional batches can contain queries only belonging to that partition. > On trying it in 3.6 I got this exception as expected: > InvalidRequest: Error from server: code=2200 [Invalid query] > message="Batch with conditions cannot span multiple partitions" > > On trying single partition batch with multiple LWT statements cassandra > accepted them at times and rejected the complete batch statement based on > the other LWT. I mean in the below batch > BEGIN BATCH > Statement 1 IF SOME CONDITION; > Statement 2 IF SOME CONDITION2; > Statement 3; > APPLY BATCH; > > LWT of Either of Statement 1/2 was being observed of batch to be > successful or fail and as per this doc > <https://docs.datastax.com/en/cql/3.3/cql/cql_reference/batch_r.html> "If > one statement in a batch is a conditional update, the conditional logic > must return true, or the entire batch fails." Thats what must be > essentially happening and therefore having more than one lwt may not make a > lot of sence. > > One query still remains though, can single partition batch considered to > be isolated per replica. Say if there are 5 rows in a partition and we are > updating all using lwt the clients should read either all of them old or > all of them during batch update. > > Will be glad if someone can clarify the above doubt. > > > > On Tue, Sep 6, 2016 at 11:18 PM, Bhuvan Rawal <bhu1ra...@gmail.com > <javascript:_e(%7B%7D,'cvml','bhu1ra...@gmail.com');>> wrote: > >> Hi, >> >> We are working to solve on a multi threaded distributed design which in >> which a thread reads current state from Cassandra (Single partition ~ 20 >> Rows), does some computation and saves it back in. But it needs to be >> ensured that in between reading and writing by that thread any other thread >> should not have saved any operation on that partition. >> >> We have thought of a solution for the same - *having a write_time column* >> in the schema and making it static. Every time the thread picks up a job >> read will be performed with LOCAL_QUORUM. While writing into Cassandra >> batch will contain a LWT (IF write_time is read time) otherwise read will >> be performed and computation will be done again and so on. This will ensure >> that while saving partition is in a state it was read from. >> >> In order to avoid race condition we need to ensure couple of things: >> >> 1. While saving data in a batch with a single partition (*Rows may be >> Updates, Deletes, Inserts)* are they Isolated per replica node. (Not >> necessarily on a cluster as a whole). Is there a possibility of client >> reading partial rows? >> >> 2. If we do a LOCAL_QUORUM read and LOCAL_QUORUM writes in this case >> could there a chance of inconsistency in this case (When LWT is being used >> in batches). >> >> 3. Is it possible to use multiple LWT in a single Batch? In general how >> does LWT performs with Batch and is Paxos acted on before batch execution? >> >> Can someone help us with this? >> >> Thanks & Regards, >> Bhuvan >> >> >
