out of memory error

Greetings,

During testing of our application we ran into a very odd error:

very randomly during the test the postgresql log file showed a "ERROR:
53200: out of memory"
we changed the logging configuration to log statements causing errors
and found the error to be caused by a SELECT,

here is the relevant info from postgresql log file :

ERROR: 53200: out of memory
DETAIL: Failed on request of size 188
LOCATION: AllocSetAlloc, aset.c:700

Interestingly the box did not OOM (i.e nothing in /var/log/messages)
running RHAS3 with PG 7.4.2

-bash-2.05b$ id
uid=26(postgres) gid=26(postgres) groups=26(postgres)
-bash-2.05b$ psql -V
psql (PostgreSQL) 7.4.2
contains support for command-line editing
-bash-2.05b$ cat /etc/redhat-release
Red Hat Enterprise Linux ES release 3 (Taroon)
-bash-2.05b$ ulimit -a
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
file size (blocks, -f) unlimited
max locked memory (kbytes, -l) 4
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 7168
virtual memory (kbytes, -v) unlimited

This happens randomly, when the failing SELECT was run via psql it
executed w/o error.

Any suggestions on how this can be debugged?

-Adi