Re: [HACKERS] logical decoding of two-phase transactions

On Tue, Nov 17, 2020 at 9:05 PM Amit Kapila  wrote:
>
> On Tue, Nov 17, 2020 at 5:02 PM Ajin Cherian  wrote:
> >
> > On Tue, Nov 17, 2020 at 10:14 PM Amit Kapila  wrote:
> >
> > >
> > > Doesn't this happen only if you set replication origins? Because
> > > otherwise both PrepareTransaction() and
> > > RecordTransactionCommitPrepared() used the current timestamp.
> > >
> >
> > I was also checking this, even if you set replicating origins, the
> > preparedTransaction will reflect the local prepare time in
> > pg_prepared_xacts. pg_prepared_xacts fetches this information
> > from GlobalTransaction data which does not store the origin_timestamp;
> > it only stores the prepared_at which is the local timestamp.
> >
>
> Sure, but my question was does this difference in behavior happens
> without replication origins in any way? The reason is that if it
> occurs only with replication origins, I don't think we need to bother
> about the same because that feature is not properly implemented and
> not used as-is. See the discussion [1] [2]. OTOH, if this behavior can
> happen without replication origins then we might want to consider
> changing it.

Logical replication workers always have replication origins, right? Is
that what you meant 'with replication origins'?

IIUC logical replication workers always set the origin's commit
timestamp as the commit timestamp of the replicated transaction. OTOH,
the timestamp of PREPARE, ‘prepare’ of pg_prepared_xacts, always uses
the local timestamp even if the caller of PrepareTransaction() sets
replorigin_session_origin_timestamp. In terms of user-visible
timestamps of transaction operations, I think users might expect these
timestamps are matched between the origin and its subscribers. But the
pg_xact_commit_timestamp() is a function of the commit timestamp
feature whereas ‘prepare’ is a pure timestamp when the transaction is
prepared. So I’m not sure these timestamps really need to be matched,
though.

Regards,

-- 
Masahiko Sawada
EnterpriseDB:  https://www.enterprisedb.com/