1. A batch with updates to a single partition turns into a single mutation so partition writes aren't possible (so may as well use Unlogged batches) 2. Yes, so use local_serial or serial reads and all updates you want to honor LWT need to be LWT as well, this way everything is buying into the same protocol and behaving accordingly. 3. LWT works with batch (has to be same partition). https://docs.datastax.com/en/cql/3.1/cql/cql_reference/batch_r.html if condition doesn't fire none of the batch will (same partition will mean it'll be the same mutation anyway so there really isn't any magic going on).
Your biggest issue with such a design will be contention (as it would with an rdbms with say row locking), as by intent you're making all reads and writes block until any pending ones are complete. I'm sure there are a couple things I forgot but this is the standard wisdom. Regards, Ryan Svihla > On Sep 11, 2016, at 3:49 PM, Jens Rantil <jens.ran...@tink.se> wrote: > > Hi, > > This might be off-topic, but you could always use Zookeeper locking and/or > Apache Kafka topic keys for doing things like this. > > Cheers, > Jens > >> On Tuesday, September 6, 2016, Bhuvan Rawal <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 > > > -- > Jens Rantil > Backend engineer > Tink AB > > Email: jens.ran...@tink.se > Phone: +46 708 84 18 32 > Web: www.tink.se > > Facebook Linkedin Twitter >
