Re: Logical Replication vs. 2PC

On 20.03.21 03:17, Amit Kapila wrote:
> Are you saying that users might use the same GID which we have
> constructed internally (say by combining origin and xid: originid_xid)
> and then there will be conflict while replaying such transactions?

No, I was pondering about a user doing (in short sequence):

..
PREPARE TRANSACTION 'foobar';
COMMIT PREPARED 'foobar';

BEGIN;
...
PREPARE TRANSACTION 'foobar';
COMMIT PREPARED 'foobar';

> Right and even for one subscription that can lead to blocking
> transactions. But isn't it similar to what we get for a primary key
> violation while replaying transactions?

Sure, it's a conflict that prevents application. A primary key conflict
may be different in that it does not eventually resolve, though.

> In that case, we suggest users
> remove conflicting rows, so in such cases, we can recommend users to
> commit/rollback such prepared xacts?

Right, if you use gids, you could ask the user to always provide unique
identifiers and not reuse them on any other node. That's putting the
burden of coming up with unique identifiers on the user, but that's a
perfectly fine and reasonable thing to do. (Lots of other systems out
there requiring a unique request id or such, which would get confused if
you issue requests with duplicate ids.)

Regards

Markus