Re: pg_stat_statements: duplicated external query texts with MSY2

Julien Rouhaud <rjuju123(at)gmail(dot)com> writes:
> On Mon, Jun 8, 2020 at 11:28 PM legrand legrand
> <legrand_legrand(at)hotmail(dot)com> wrote:
>> pgbench -i postgres
>> pgbench -c20 -t5 postgres
>> generates the attached pgss_query_texts.stat,
>> where "BEGIN" and "UPDATE pgbench_accounts SET abalance = abalance + $1 WHERE aid = $2"
>> appears 20 times ...

> Is the duplication only in the query text file? Looking at the code
> the query text part is stored holding a shared lwlock, so it seems
> like an expected behavior (less overhead but might store duplicated
> query text)

I agree, this looks like operating-as-designed: different processes can
store the same query text and only later discover that they were creating
duplicate hash table entries. It's a bit surprising that the duplication
would be reproducible, but it just depends on timing. Maybe this is
telling us something about how scheduling works under MSYS2.

regards, tom lane