Postgresql suddenly shutdown. Please help

Hello,

First about my english,

I have a server (Dual Petium IV Xeon 2Ghz, 512 MB RAM, 64 GB SCSI HD) in Linux
RH 8.0, using Postgresql 7.3, compiled from the sources.

Well, I have detected two times that the sever after runing about 40 or 50
days, the postgres database server die.

The second time that the database died, when I turned on the monitor, I saw on
the login text screen some messages like these:

Out of Memory: killed process 20003 (postmaster)
...
... (idem)
...
Out of Memory: killed process 1055 (http)
...

I think that the system is "out of memory", and is killing processes, for
freeing memory... Therefore postgres die. I say that this is what i suppose,
but, why ?

I think that this high memory hungry, could be relationed with postgres. In
the 40-50 days that postgres lives, I have to say that I've never do a manual
vacuum, because the server is so far away and I don't trust in automatic
vacuum that could be lock until all transactions end.

Here are, a bit of the "serverlog" and "postgresql.conf" files:

================================================
tail -40 serverlog
================================================
LOG: statistics collector process (pid 2672) was terminated by signal 9
LOG: statistics collector process (pid 2674) was terminated by signal 9
LOG: statistics collector process (pid 2677) was terminated by signal 9
LOG: statistics collector process (pid 2680) was terminated by signal 9
LOG: statistics collector process (pid 2682) was terminated by signal 9
LOG: statistics collector process (pid 2685) was terminated by signal 9
LOG: statistics collector process (pid 2687) was terminated by signal 9
LOG: statistics collector process (pid 2690) was terminated by signal 9
LOG: server process (pid 2676) was terminated by signal 9
LOG: terminating any other active server processes
WARNING: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
LOG: statistics collector process (pid 2692) was terminated by signal 9
LOG: statistics collector process (pid 2694) was terminated by signal 9
FATAL: The database system is in recovery mode
LOG: statistics collector process (pid 2697) was terminated by signal 9
LOG: statistics collector process (pid 2700) was terminated by signal 9
FATAL: The database system is in recovery mode
LOG: statistics collector process (pid 2702) was terminated by signal 9
LOG: statistics collector process (pid 2704) was terminated by signal 9
LOG: statistics collector process (pid 2706) was terminated by signal 9
LOG: all server processes terminated; reinitializing shared memory and
semaphores
LOG: statistics collector process (pid 2708) was terminated by signal 9
LOG: startup process (pid 2710) was terminated by signal 9
LOG: aborting startup due to startup process failure
LOG: database system was interrupted at 2003-05-15 09:39:04 CEST
LOG: checkpoint record is at 0/244C2B84
LOG: redo record is at 0/244C2B84; undo record is at 0/0; shutdown TRUE
LOG: next transaction id: 20147; next oid: 119397
LOG: database system was not properly shut down; automatic recovery in
progress
LOG: ReadRecord: record with zero length at 0/244C2BC4
LOG: redo is not required
LOG: database system is ready
LOG: fast shutdown request
LOG: shutting down
LOG: database system is shut down

================================================
postgresql.conf
================================================
#
# Connection Parameters
#
#tcpip_socket = false
#ssl = false

max_connections = 128
#superuser_reserved_connections = 2

#port = 5432
#hostname_lookup = false
#show_source_port = false

#unix_socket_directory = ''
#unix_socket_group = ''
#unix_socket_permissions = 0777 # octal

#virtual_host = ''

#krb_server_keyfile = ''

#
# Shared Memory Size
#
shared_buffers = 1024 # 2*max_connections, min 16, typically 8KB each
#max_fsm_relations = 100 # min 10, fsm is free space map, ~40 bytes
#max_fsm_pages = 10000 # min 1000, fsm is free space map, ~6 bytes
#max_locks_per_transaction = 64 # min 10
wal_buffers = 8 # min 4, typically 8KB each

#
# Non-shared Memory Sizes
#
sort_mem = 8192 # min 64, size in KB
#vacuum_mem = 8192 # min 1024, size in KB

==========================================================

Please, how can I resolve this problem ? Why postgres shuts down ?

Thanks very much.