Re: pg_stat_statments queryid

On Thu, May 24, 2012 at 4:26 PM, Peter Geoghegan <peter@2ndquadrant.com> wrote:
> On 24 May 2012 11:50, Magnus Hagander <magnus@hagander.net> wrote:
>> Was there any actual reason why we didn't end up exposing queryid in
>> the pg_stat_statements view?
>>
>> It would be highly useful when tracking changes over time. Right now I
>> see people doing md5(query) to do that, which is a lot more ugly (and
>> obviously uses more space and is slow, too).
>
> Right. I continue to maintain that this is a good idea. I raised the
> issue more than once. However, my proposal was not accepted by Tom and
> Robert, apparently on the basis that queryId's actual value was
> partially dictated by things like the endianness of the architecture
> used, and the value of OIDs when serialising and subsequently hashing
> the post-analysis tree.
>
> What I'd like to be able to do is aggregate this information over time
> and/or across standbys in a cluster, as queries are evicted and
> subsequently re-entered into pg_stat_statement's shared hash table.

That's exactly the usecase I'm looking at here, except it's not
actually across standbys in this case.


> Now, there are situations were this isn't going to work, like when a
> third-party logical replication system is used. That's unfortunate,
> but I wouldn't expect it makes the information any less useful to the
> large majority of people. I'd also credit our users with being
> discerning enough to realise that they should not jump to the
> conclusion that the value will be stable according to any particular
> standard.

As long as it's documented as such, I don't see a problem with that at all.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/