On August 20, 2015 at 2:17:31 AM, Simon Riggs (simon@2ndquadrant.com(mailto:simon@2ndquadrant.com)) wrote:
> On 18 August 2015 at 21:03, Paul Ramsey wrote:
>
> > So I need a way to either (a) notice when I already have a (old) copy
> > of the library loaded and avoid trying to setup the GUC in that case
> > or (b) set-up the GUC in a somewhat less brittle way than
> > DefineCustomStringVariable() allows, something that can overwrite
> > things instead of just erroring out.
>
> Are you trying to preserve the in-memory state across upgrade as well? It sounds unlikely we can support that
directlyin the general case.
I’m not sure what you mean by this.
> Sounds like we need RedefineCustomStringVariable()
Yes, if that had existed we would not have had any problems (as long as it delegated back to Define..() in the case
wherethe variable hadn’t been created yet…, since one of the problems is knowing if/to-what-extent a custom variable
hasalready been defined).
We do now have a fix, which involved copying about 100 lines of core code (find_option, guc_var_compare,
guc_name_compare)up, that does a low level search to see if there is a config_generic for a particular variable name,
andif so whether it’s a placeholder or not. The presence of a non-placeholding definition is used as a “uh oh, there’s
alreadya library in here” warning which keeps us from re-defining the variable and causing trouble.
P.
>
> --
> Simon Riggs http://www.2ndQuadrant.com/(http://www.2ndquadrant.com/)
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
