Re: Question about StartLogicalReplication() error path

Hi,

On 2021-06-11 13:15:11 -0400, Robert Haas wrote:
> On Fri, Jun 11, 2021 at 2:23 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> > * The comment acknowledges that a user might expect an error in that
> > case; but doesn't really address why the user would expect an error,
> > and why it's OK to violate that expectation.
>
> This code was written by Andres, so he'd be the best person to comment
> on it, but it seems to me that the comment does explain this, and that
> it's basically the same explanation as what Amit said. If the client
> doesn't have to do anything for a certain range of WAL and just
> acknowledges it, it would under your proposal have to also durably
> record that it had chosen to do nothing, which might cause extra
> fsyncs, potentially lots of extra fsyncs if this happens frequently
> e.g. because most tables are filtered out and the replicated ones are
> only modified occasionally.

Yes, that's the motivation.

> I'm not sure that it would be a good trade-off to have a tighter
> sanity check at the expense of adding that overhead.

Especially because it very well might break existing working setups...

Greetings,

Andres Freund