On 18.03.21 10:45, Amit Kapila wrote:
While reviewing/testing subscriber-side work for $SUBJECT [1], I noticed a problem that seems to need a broader discussion, so started this thread. We can get prepare for the same GID more than once for the cases where we have defined multiple subscriptions for publications on the same server and prepared transaction has operations on tables subscribed to those subscriptions. For such cases, one of the prepare will be successful and others will fail in which case the server will send them again. Once the commit prepared is done for the first one, the next prepare will be successful. Now, this is not ideal but will work.
That's assuming you're using the same gid on the subscriber, which does not apply to all use cases. It clearly depends on what you try to achieve by decoding in two phases, obviously.
We clearly don't have this issue in BDR, because we're using xids (together with a node id) to globally identify transactions and construct local (per-node) gids that don't clash.
(Things get even more interesting if you take into account that users may reuse the same gid for different transactions. Lag between subscriptions could then lead to blocking between different origin transactions...)
Regards Markus
