Re: Record SET session in VariableSetStmt

On 10/6/22 2:28 PM, Julien Rouhaud wrote:
> On Thu, Oct 06, 2022 at 02:19:32PM +0200, Drouvot, Bertrand wrote:
>>
>> On 10/6/22 1:18 PM, Julien Rouhaud wrote:
>>
>>> 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?
> 
> It's because until now jumbling of utility statements was just hashing the
> query text, which is quite terrible.  This was also implying getting different
> queryids for things like this:
> 
> =# select query, queryid from pg_stat_statements where query like '%work_mem%';;
>           query         |       queryid
> -----------------------+----------------------
>   SeT work_mem = 123465 | -1114638544275583196
>   Set work_mem = 123465 | -1966597613643458788
>   SET work_mem = 123465 |  4161441071081149574
>   seT work_mem = 123465 |  8327271737593275474
> (4 rows)
> 
> If we move to a real jumbling of VariableSetStmt, we should keep the rules
> consistent with the rest of the jumble code and ignore an explicit "SESSION" in
> the original command.

Understood, so I agree that it makes sense to keep the jumbling behavior 
consistent and so keep the same queryid for statements that are 
semantically identical.

Thanks for your feedback!

Regards,

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