Re: [HACKERS] Function to control physical replication slot

On 2017-04-12 20:15:52 -0400, Peter Eisentraut wrote:
> On 4/11/17 05:15, Magnus Hagander wrote:
> > Is there a particular reason we don't have a function to *set* the
> > restart_lsn of a replication slot, other than to drop it and recreate it?
> 
> I suppose there could be lots of problems if the LSN you specify isn't
> valid.  And it might be hard to determine whether a given LSN is valid.

As long as we're only talking about the LSN of a physical slot (and not
the xmin) I'm not sure it's that important that it's valid, as long as
it's not in the future.  But we could otherwise pretty easily assert
that the new value has to be old_value <= new_value <=
GetRedoRecPtr()/GetFlushRecPtr().  That should be sufficient for both of
your use-cases afaics?

- Andres