Στις 9/11/24 16:05, ο/η Achilleas Mantzios έγραψε:
Στις 9/11/24 12:49, ο/η Tomas Vondra έγραψε:
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.
Thank you Tomas, do you have linux-perf in mind? How could we get the
CPU profiles of the two ? Just in case it was not clear, the tests
were done on the same VM, at the same time, having the two DBs
listening on different ports. Kinda spooky from my part to do that on
the production system, but I wanted everything to be the same (latency
to/from the ms sql, etc) except the pgsql version, to prove my
assumption, and it seems pgsql version is what makes the difference
(in conjunction of course with tds_fdw ) .
Meaning there are CPP directives in the tds_fdw source making it behave
differently according to the Postgresql version. The two tds_fdw's have
the same version.
regards
