tds_fdw : Severe performance degradation from postgresql 10.23 to 16.4

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.