On 17 August 2017 at 09:33, Andres Freund <and...@anarazel.de> wrote:
> On 2017-08-16 21:25:48 -0400, Robert Haas wrote: > > On Wed, Aug 16, 2017 at 5:55 PM, Andres Freund <and...@anarazel.de> > wrote: > > > I think we should constrain the API to only allow later LSNs than > > > currently in the slot, rather than arbitrary ones. That's why I was > > > thinking of "forward". I'm not convinced it's a good / safe idea to > > > allow arbitrary values to be set. > > > > Maybe I shouldn't play the devil's advocate here, but isn't a feature > > like this by definition only for people who Know What They Are Doing? > > If so, why not let them back the slot up? I'm sure that will work out > > just fine. They Know What They Are Doing. > > I have yet to hear a reason for allowing to move things backward etc. So > I'm not sure what the benefit would be. But more importantly I'd like to > make this available to non-superusers at some point, and there I think > it's more important that they can't do bad things. The reason for > allowing it for non-superusers is that I think it's quite a useful > function to be used by an automated system. E.g. to ensure enough, but > not too much, WAL is available for a tertiary standby both on the actual > primary and a failover node. > I strongly agree. If you really need to move a physical slot back (why?) you can do it with an extension that uses the low level APIs. But I can't see why you would want to. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
