Re: [GENERAL] currval and DISCARD ALL

On Tue, Apr 16, 2013 at 12:13:48PM -0700, Adrian Klaver wrote:
> On 04/16/2013 08:07 AM, Nigel Heron wrote:
> >
> >On 04/15/2013 05:57 PM, Adrian Klaver wrote:
> >>On 04/15/2013 02:42 PM, Nigel Heron wrote:
> >>>Hi,
> >>>is there a way to clear the session state of sequence values fetched by
> >>>currval(regclass)? "DISCARD ALL" doesn't seem to do it.
> >>>
> ><snip>
> >>Might want to take a look at:
> >>
> >>http://www.depesz.com/2012/12/02/what-is-the-point-of-bouncing/
> >>
> >>for some hints on dealing with sequences and pgBouncer.
> >>
> >
> >thanks, I read it (his blogs are always interesting!). I'm not disputing
> >that calling currval() at the wrong time is a bad idea.
> >I'm just wondering why DISCARD ALL clears everything but this?
> 
> Well per the docs:
> 
> http://www.postgresql.org/docs/9.2/interactive/sql-discard.html
> 
> DISCARD ALL
> 
> is equivalent to:
> 
> SET SESSION AUTHORIZATION DEFAULT;
> RESET ALL;
> DEALLOCATE ALL;
> CLOSE ALL;
> UNLISTEN *;
> SELECT pg_advisory_unlock_all();
> DISCARD PLANS;
> DISCARD TEMP;
> 
> AFAIK, none of the above affect sequences.

I think his point is why don't we clear currval() on DISCARD ALL?  I
can't think of a good reason we don't.  He is saying currval() should
throw an error after DISCARD ALL:
test=> SELECT currval('seq');ERROR:  currval of sequence "seq" is not yet defined in this session

I have moved this thead to hackers to get comments.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +