On Wed, Dec 8, 2021 at 5:54 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Wed, Dec 8, 2021 at 12:36 PM Masahiko Sawada <sawada.m...@gmail.com> wrote: > > > > On Wed, Dec 8, 2021 at 3:50 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > On Wed, Dec 8, 2021 at 11:48 AM Masahiko Sawada <sawada.m...@gmail.com> > > > wrote: > > > > > > > > > > > > > > Can't we think of just allowing prepare in this case and updating the > > > > > skip_xid only at commit time? I see that in this case, we would be > > > > > doing prepare for a transaction that has no changes but as such cases > > > > > won't be common, isn't that acceptable? > > > > > > > > In this case, we will end up committing both the prepared (empty) > > > > transaction and the transaction that updates the catalog, right? > > > > > > > > > > Can't we do this catalog update before committing the prepared > > > transaction? If so, both in prepared and non-prepared cases, our > > > implementation could be the same and we have a reason to accomplish > > > the catalog update in the same transaction for which we skipped the > > > changes. > > > > But in case of a crash between these two transactions, given that > > skip_xid is already cleared how do we know the prepared transaction > > that was supposed to be skipped? > > > > I was thinking of doing it as one transaction at the time of > commit_prepare. Say, in function apply_handle_commit_prepared(), if we > check whether the skip_xid is the same as prepare_data.xid then update > the catalog and set origin_lsn/timestamp in the same transaction. Why > do we need two transactions for it?
I meant the two transactions are the prepared transaction and the transaction that updates the catalog. If I understand your idea correctly, in apply_handle_commit_prepared(), we update the catalog and set origin_lsn/timestamp. These are done in the same transaction. Then, we commit the prepared transaction, right? If the server crashes between them, skip_xid is already cleared and logical replication starts from the LSN after COMMIT PREPARED. But the prepared transaction still exists on the subscriber. Regards, -- Masahiko Sawada EDB: https://www.enterprisedb.com/
