Re: Record SET session in VariableSetStmt

Hi,

On 10/6/22 1:18 PM, Julien Rouhaud wrote:
> Hi,
> 
> On Thu, Oct 06, 2022 at 12:57:17PM +0200, Drouvot, Bertrand wrote:
>> Hi hackers,
>>
>> "SET local" is currently recorded in VariableSetStmt (with the boolean
>> is_local) but "SET session" is not.
>>
>> Please find attached a patch proposal to also record "SET session" so that
>> VariableSetStmt records all the cases.
>>
>> Remark: Recording "SET session" will also help for the Jumbling work being
>> done in [1].
> 
> I don't think it's necessary.  SET and SET SESSION are semantically the same

Thanks for your feedback!

> so
> nothing should rely on how exactly someone spelled it.  This is also the case
> for our core jumbling code, where we guarantee (or at least try to) that two
> semantically identical statements will get the same queryid, and therefore
> don't distinguish eg. LIKE vs ~~.

Agree, but on the other hand currently SET and SET SESSION are recorded 
with distinct queryid:

postgres=# select calls, query, queryid from pg_stat_statements;
  calls |                    query                    |       queryid
-------+---------------------------------------------+----------------------
      2 | select calls, query from pg_stat_statements | -6345508659980235519
      1 | set session enable_seqscan=1                | -3921418831612111986
      1 | create extension pg_stat_statements         | -1739183385080879393
      1 | set enable_seqscan=1                        |  7925920505912025406
(4 rows)

and this behavior would change with the Jumbling work in progress in [1] 
(mentioned up-thread) if we don't record "SET SESSION".

I think that would make sense to keep the same behavior, what do you think?

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com