I agree with your description. But the documentation https://apacheignite. readme.io/docs/transactions is misleading in stating that no read locks are acquired (says "READ_COMMITTED - Data is read without a lock and is never cached in the transaction itself."). Which should be wrong. Read locks are acquired but they are released as soon as the read is complete (and they are not held until the transaction commits or rolls back).
Thanks, On Wed, Jul 25, 2018 at 10:33 AM, Valentin Kulichenko < valentin.kuliche...@gmail.com> wrote: > Hi John, > > Read committed isolation typically implies that lock on read is not held > throughout the transaction lifecycle, i.e. released right after read is > completed (in Ignite this just means that no lock is required at all). This > semantic allows second read to get an updated value that was already > committed by another transaction. See Wikipedia description for example: > https://en.wikipedia.org/wiki/Isolation_(database_systems)#Read_committed > > What you're describing is REPEATABLE_READ isolation which guarantees that > subsequent reads return the same value. In Ignite it's achieved by > acquiring lock on read and releasing it only on commit/rollback. > > -Val > > On Wed, Jul 25, 2018 at 10:12 AM John Wilson <sami.hailu...@gmail.com> > wrote: > > > Hi, > > > > Consider the following transaction where we read key 1 twice. > > > > try (Transaction tx = Ignition.ignite().transactions().txStart( > PESSIMISTIC, > > READ_COMMITTED)) { > > cache.get(1); > > //... > > cache.get(1); > > tx.commit(); > > } > > > > According to the documentation here, > > https://apacheignite.readme.io/docs/transactions, data is read without a > > lock and is never cached. If that is the case, then how do we avoid a > dirty > > read on the second cache.get(1)? Another uncommitted transaction may > update > > the key between the first and second reads. > > > > In most RDMS, a READ_COMMITTED isolation level, acquires locks for both > > read and writes. The read lock is released after a read while the write > > lock is held until the transaction completes. So for the above example, I > > expect a read lock on each cache.get(1). > > > > > > Thanks, > > >
