Re: tds_fdw : Severe performance degradation from postgresql 10.23 to 16.4

On 11/8/24 20:32, Achilleas Mantzios wrote:
> Dear All, 
>
> we have hit a serious performance regression going from 10.23 → 16.4 as
> far as tds_fdw (MS SQL) FDW is concerned. To cut the long story short, I
> recreated the good fast “old” (pgsql 10) setup on the same vm as the
> slow “new” (pgsql 16). Here is the bug report on github :
>
> https://github.com/tds-fdw/tds_fdw/issues/371
>
> All environment on the two pgsql clusters is shared (freetds version,
> tds_fdw, gcc, llvm). Only thing differs are pgsql versions. The speed on
> the old pgsql 10.23 is about 10 to 20 times higher than pgsql 16.4 . |
> Setting client_min_messages TO debug3 does yield identical output on the
> two systems.
> |
>
> The new pgsql 16.4 shows 100% CPU usage during the query execution.
>
> I know we are pretty much alone with this, but it would be very nice if
> anyone could help, see smth we are missing or guide us via the right path.
>

I have little experience with tds_fdw, and can't investigate that
locally. But it might be interesting to compare CPU profiles for the two
(slow and fast) cases. Chances are the difference will be an indication
regarding what got that slower. It might be something in PG or in the
FDW, hard to say.

regards

--
Tomas Vondra