RE: Failed transaction statistics to measure the logical replication progress

On Monday, November 1, 2021 10:18 PM I wrote:
> On Thursday, October 28, 2021 11:19 PM I wrote:
> > I've created a new patch that extends pg_stat_subscription_workers to
> > include other transaction statistics.
> >
> > Note that this patch depends on v18 patch-set in [1]...
> Rebased based on the v19 in [1].
I'd like to add one more explanation about the latest patches for review.

On Thursday, October 28, 2021 11:19 PM I wrote:
> (2)
> Updates of stats on the view at either commit prepared or rollback prepared
> time.
> This means we don't lost prepared transaction size even after server restart
> and user can see the results of two phase operation at those timings.
There is another reason I had to treat 'prepare' message like above.
Any reviewer might think that sending prepared bytes to stats collector
and making the bytes survive over the restart is too much.

But, we don't know if the prepared transaction is processed
by commit prepared or rollback prepared at 'prepare' time.
An execution of commit prepared needs to update the column of xact_commit and
xact_commit_bytes while rollback prepared does the column of xact_abort
and xact_abort_bytes where this patch is introducing.

Therefore, even when we can calculate the bytes of prepared txn at prepare time,
it's *not* possible to add the transaction bytes to either stats column of
bytes sizes and clean up the bytes. Then, there was a premise
that we should not lose the prepared txn bytes by the shutdown
so my patch has become the implementation described above.

Best Regards,
Takamichi Osumi