Anton, Is such behavior observed for 2PC or for 1PC optimization? Does not it mean that the things can be even worse and an inconsistent write is possible on a backup? E.g. in scenario: 1. txA writes a value 1 for the key on primary. 2. txA unlocks the key on primary. 3. txA freezes before updating backup. 4. Very fast and lucky txB writes a value 2 for the key on primary and backup. 5. txB wakes up and writes 1 for the key. 6. As result there is 2 on primary and 1 on backup.
Naively it seems that locks should be released after all replicas are updated. ср, 10 июл. 2019 г. в 16:36, Anton Vinogradov <a...@apache.org>: > > Folks, > > Investigating now unexpected repairs [1] in case of ReadRepair usage at > testAccountTxNodeRestart. > Updated [2] the test to check is there any repairs happen. > Test's name now is "testAccountTxNodeRestartWithReadRepair". > > Each get method now checks the consistency. > Check means: > 1) tx lock acquired on primary > 2) gained data from each owner (primary and backups) > 3) data compared > > Sometime, backup may have obsolete value during such check. > > Seems, this happen because tx commit on primary going in the following way > (check code [2] for details): > 1) performing localFinish (releases tx lock) > 2) performing dhtFinish (commits on backups) > 3) transferring control back to the caller > > So, seems, the problem here is that "tx lock released on primary" does not > mean that backups updated, but "commit() method finished at caller's > thread" does. > This means that, currently, there is no happens-before between > 1) thread 1 committed data on primary and tx lock can be reobtained > 2) thread 2 reads from backup > but still strong HB between "commit() finished" and "backup updated" > > So, it seems to be possible, for example, to gain notification by a > continuous query, then read from backup and gain obsolete value. > > Is this "partial happens before" behavior expected? > > [1] https://issues.apache.org/jira/browse/IGNITE-11973 > [2] https://github.com/apache/ignite/pull/6679/files > [3] > org.apache.ignite.internal.processors.cache.distributed.dht.GridDhtTxLocal#finishTx -- Best regards, Ivan Pavlukhin
