[ants_a]

Interesting why this magic would be needed. Vanilla Postgres does support quorum commit which can do this. You can also set up the equivalent multi-AZ cluster with Patroni, and (modulo bugs) it does the necessary coordination to make sure to promote primaries in a way that does not lose transactions or makes visible a transaction that is not durable.

There still is a Postgres deficiency that makes something similar to this pattern possible. Non-replicated transactions where the client goes away mid-commit become visible immediately. So in the example, if T1 happens on a partitioned leader, disconnects during commit, T2 also happens on a partitioned node, and T3 and T4 happen later on a new leader, you would also see the same result. However, this does not jive with the statement that fault injection was not done in this test.

Edit: did not notice the post that this pattern can be explained by inconsistent commit order on replica and primary. Kind of embarrassing given I've done a talk proposing how to fix that.

[sontek]

Link the talk video

[ants_a]

https://www.youtube.com/watch?v=vz-dhwSpjOw