RE: logical decoding and replication of sequences, take 2

Dear Amit, Tomas,

> > >
> > > I am wondering that instead of building the infrastructure to know
> > > whether a particular change is transactional on the decoding side,
> > > can't we have some flag in the WAL record to note whether the change
> > > is transactional or not? I have discussed this point with my colleague
> > > Kuroda-San and we thought that it may be worth exploring whether we
> > > can use rd_createSubid/rd_newRelfilelocatorSubid in RelationData to
> > > determine if the sequence is created/changed in the current
> > > subtransaction and then record that in WAL record. By this, we need to
> > > have additional information in the WAL record like XLOG_SEQ_LOG but we
> > > can probably do it only with wal_level as logical.
> > >
> >
> > I may not understand the proposal exactly, but it's not enough to know
> > if it was created in the same subxact. It might have been created in
> > some earlier subxact in the same top-level xact.
> >
> 
> We should be able to detect even some earlier subxact or top-level
> xact based on rd_createSubid/rd_newRelfilelocatorSubid.

Here is a small PoC patchset to help your understanding. Please see attached
files.

0001, 0002 were not changed, and 0004 was reassigned to 0003.
(For now, I focused only on test_decoding, because it is only for evaluation purpose.)

0004 is what we really wanted to say. is_transactional is added in WAL record, and it stores
whether the operations is transactional. In order to distinguish the status, rd_createSubid and
rd_newRelfilelocatorSubid are used. According to the comment, they would be a valid value
only when the relation was changed within the transaction
Also, sequences_hash was not needed anymore, so it and related functions were removed.

How do you think?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED