Now, if it's simpler to just xlog the gid at COMMIT PREPARED time when wal_level >= logical I don't think that's the end of the world. But since we already have almost everything we need in memory, why not just stash the gid on ReorderBufferTXN?
I have been through this thread... And to be honest, I have a hard time understanding for which purpose the information of a 2PC transaction is useful in the case of logical decoding. The prepare and commit prepared have been received by a node which is at the root of the cluster tree, a node of the cluster at an upper level, or a client, being in charge of issuing all the prepare queries, and then issue the commit prepared to finish the transaction across a cluster. In short, even if you do logical decoding from the root node, or the one at a higher level, you would care just about the fact that it has been committed.
in any state. So there three records in the WAL: PREPARE, PRECOMMIT, COMMIT_PREPARED and recovery can involve either all of them, either PRECOMMIT+COMMIT_PREPARED either just COMMIT_PREPARED.
That's your modified Pg though.
This 2pc logical decoding patch proposal is for core and I think it just confused things to introduce discussion of unrelated changes made by your product to the codebase.