Ok, I got it Thanks Alan Le lun. 9 sept. 2019 à 20:34, Alan Gates <alanfga...@gmail.com> a écrit :
> Not simultaneously. In Hive 2 the first delete started will obtain a > lock, and the second will have to wait. In Hive 3, the first one to commit > will win and the second will fail (at commit time). > > Alan. > > On Mon, Sep 9, 2019 at 10:55 AM David Morin <morin.david....@gmail.com> > wrote: > >> Thanks Alan, >> >> When you say "you just can't have two simultaneous deletes in the same >> partition", simultaneous means for the same transaction ? >> If a create 2 "transactions" for 2 deletes on the same table/partition it >> works. Am I right ? >> >> >> Le lun. 9 sept. 2019 à 19:04, Alan Gates <alanfga...@gmail.com> a écrit : >> >>> In Hive 2 update and delete take what are called semi-shared locks >>> (meaning they allow shared locks through, while not allowing other >>> semi-shared locks), and insert and select take shared locks. So you can >>> insert or select while deleting, you just can't have two simultaneous >>> deletes in the same partition. >>> >>> The reason insert can take a shared lock is because Hive does not >>> enforce uniqueness constraints, so there's no concept of overwriting an >>> existing row. Multiple inserts can also proceed simultaneously. >>> >>> This changes in Hive 3, where update and delete also take shared locks >>> and a first committer wins strategy is employed instead. >>> >>> Alan. >>> >>> On Mon, Sep 9, 2019 at 8:29 AM David Morin <morin.david....@gmail.com> >>> wrote: >>> >>>> Hello, >>>> >>>> I use in production HDP 2.6.5 with Hive 2.1.0 >>>> We use transactional tables and we try to ingest data in a streaming >>>> way (despite the fact we still use Hive 2) >>>> I've read some docs but I would like some clarifications concerning the >>>> use of Locks with transactional tables. >>>> Do we have to use locks during insert or delete ? >>>> Let's consider this pipeline: >>>> 1. create a transaction for delete and related lock (shared) >>>> 2. create delta directory + file with this new transaction (original >>>> transaction != current with original is the transaction used for the last >>>> insert) >>>> 3 Same steps 1 and 2 for Insert (except original transaction = current) >>>> 4. commit transactions >>>> >>>> Can we use Shared lock here ? Thus select queries can still be used >>>> >>>> Thanks >>>> David >>>> >>>> >>>> >>>> >>>> >>>> >>>>
