As far as I remember, there is an optimization in Cassandra to manage Paxos ballot per table. So asking a Paxos operation to span multiple tables (even if same partition key) would require a lot of changes in the current impl.
The question has already been raised, you may want to convince the committers by adding some comments here: https://issues.apache.org/jira/browse/CASSANDRA-10085 On Mon, Oct 24, 2016 at 9:58 AM, Mickael Delanoë <delanoe...@gmail.com> wrote: > Hi, > > I would like to use lightweight transaction inside a batch but the request > is rejected by cassandra, however I think this is a use case than could be > handled without problem. > Below is what I wanted to do. > > I am using cassandra 3.7. > > CREATE KEYSPACE test_ksp WITH replication = {'class': 'SimpleStrategy', > 'replication_factor': '1'}; > > CREATE TABLE test_ksp.item ( > user_id bigint, > item_id text, > item_value text, > item_key1 text, > item_key2 text, > PRIMARY KEY ((user_id), item_id)); > > CREATE TABLE test_ksp.item_id_by_key ( > user_id bigint, > item_key text, > item_id text, > PRIMARY KEY ((user_id), item_key)); > > USE test_ksp; > > BEGIN BATCH > INSERT INTO item (user_id, item_id, item_value, item_key1, item_key2) > values (1,'i11','item-C', 'key-XYZ-123', 'key-ABC-789') IF NOT EXISTS; > INSERT INTO item_id_by_key (user_id, item_key, item_id) VALUES (1, > 'key-XYZ-123', 'i11'); > INSERT INTO item_id_by_key (user_id, item_key, item_id) VALUES (1, > 'key-ABC-789', 'i11'); > APPLY BATCH; > > > So as you can see this is a batch that targets 2 tables but with the same > partition key (i.e the same target nodes). Moreover It uses only ONE > condition on one table only. > I don't understand why cassandra returns an error "Batch with conditions > cannot span multiple tables" in that case. > > I understand that if I had used several conditions on different tables it > could be a problem, but in my case there is only one condition and moreover > I have always the same partition key for every table inside the batch. > As there is only one condition, I expected the paxos protocol just act on > this condition and as the partition keys are all the same, the paxos > protocol has only to work with the same replica nodes (not span across > multiple partition). > In my point of view this is as if the LWT was in a single statement, > except that after the LWT is accepted a complete batch has to be executed. > > Is there someone that could explain why this use case need to be rejected > by cassandra? And do you think this is something that cassandra could > handle in a future version ? > > Regards, > Mickaël > >
