FreeBSD problem under heavy load

I seem to run into a serious problem. With 6.5.x + FreeBSD 3.2, I get
a core under heavy load (16 or more concurrent users). FreeBSD 2.2.x
seems more stable but soon or later same thing happens. Examing a
core, I found it segfaulted in hash_search(). It was not possible to
get more info having a -g compiled backend becasue it did not fail if -
g was given. It is likely that random memory corruptions occured. It
is also reported by a user that he often sees:
NOTICE:  LockReplace: xid table corrupted

Note that these problems never happen on Linux (even running 128 users
are ok on Linux). Only FreeBSD is suffered as far as I can see(not
sure about other *BSD). Increasing shmem or semaphore never helps.

How to reproduce the problem:

1) obtain pgbench source from
ftp.sra.co.jp/pub/cmd/postgres/pgbench/pgbench-1.1.tar.gz

2) unpack the archive and run configure

3) edit the first line in Makefile

POSTGRESHOME = /usr/local/pgsql

4) make. you will get an executable "pgbench" there.

5) make a fresh DB (suppose it is "test")

6) initialize DB

pgbench -i test

this will take for a while

7) run the test

pgbench -n -c numeber_of_concurrent users test

I see problems with numeber_of_concurrent users ~ 16 or more.

Here are my shmem settings:

shminfo:       shmmax: 41943041        (max shared memory segment size)       shmmin:       1 (min shared memory
segmentsize)       shmmni:      32 (max number of shared memory identifiers)       shmseg:       8 (max shared memory
segmentsper process)       shmall:   10240 (max amount of shared memory in pages)
 

seminfo:       semmap:     40  (# of entries in semaphore map)       semmni:     32  (# of semaphore identifiers)
semmns:   256  (# of semaphores in system)       semmnu:     30  (# of undo structures in system)       semmsl:    256
(max# of semaphores per id)       semopm:    100  (max # of operations per semop call)       semume:     10  (max # of
undoentries per process)       semusz:     92  (size in bytes of undo structure)       semvmx:  32767  (semaphore
maximumvalue)       semaem:  16384  (adjust on exit max value)
 

Any thoughts?
--
Tatsuo Ishii