It was just the first place google turned up, I made an answer late in the evening trying to help someone out on my own free time.
Regards, Ryan Svihla > On Sep 12, 2016, at 6:34 AM, Mark Thomas <ma...@apache.org> wrote: > >> On 11/09/2016 23:07, Ryan Svihla wrote: >> 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). > > Is there a good reason for linking to the 3rd party docs rather than the > official docs in this case? I can't see one at the moment. > > The official docs appear to be: > > http://cassandra.apache.org/doc/latest/cql/dml.html#batch > > It might not matter in this particular instance but it looks as if there > is a little more to the syntax than the 3rd party docs suggest (even if > you switch to the latest version of those 3rd party docs). > > Generally, if you are going to point to docs, please point to the > official Apache Cassandra docs unless there is a very good reason not > to. (And if the good reason is that there’s a deficiency in the Apache > Cassandra docs, please make it known on the list or in a Jira so someone > can write what’s missing) > > Mark > > >> 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 >> <mailto: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 >>> <mailto: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 <mailto:jens.ran...@tink.se> >>> Phone: +46 708 84 18 32 >>> Web: www.tink.se <http://www.tink.se/> >>> >>> Facebook <https://www.facebook.com/#!/tink.se> Linkedin >>> <http://www.linkedin.com/company/2735919?trk=vsrp_companies_res_photo&trkInfo=VSRPsearchId%3A1057023381369207406670%2CVSRPtargetId%3A2735919%2CVSRPcmpt%3Aprimary> >>> Twitter >>> <https://twitter.com/tink> >
