Mark, Is there some official Apache policy on which sites it's appropriate to link to on an Apache mailing list? If so, could you please post a link to it so we can all understand the rules. Or is this your personal opinion on what you'd like to see here?
Thanks! On Mon, Sep 12, 2016 at 7:34 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> > >> > >
