update query blows out

Hi folks, sorry if the following is confusing, I have just tried to
provide the pertinent info and I have been up for more than 24 hours
working. I am getting weary....

I am having a problem with an update transaction. I need to update 4000+
records but the update query keeps blowing out postgres and at times I
am forced to restart the postmaster or reboot my server if I update
2500+ records. The query is fine with 2225 records it is just somewhere
beyond 2225 that brings the server down.

I assumed this was related to the shared memory settings but when I
tried changing those values the behavior was identical. I did not try
beyond 256 megs for shmmax.
I then tried the temporary solution of lowering the number of
shared_buffers and max_connections but that did not change anything either.
I then tried using the IN operator but that did not change anything either

I am wondering if there is some other limit that I am hitting in MacOSX
that is not related to the SHM vars.

I hope I am just overlooking something simple and that the list will
come back with some chiding and an answer :)

does anybody have any suggestions?

thank you very much,

-Shane

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SQL DETAILS:

my query is of this form:

BEGIN;

UPDATE "mytable" SET "n_filtered"=0,"n_dirty"=1 where ("s_fileName" =
'filename1' OR "s_fileName" = 'filename2' ....... OR "s_fileName" =
'filename2000') AND ("n_objId=12345);

COMMIT;

explain tells me this:

seq scan on "mytable" (cost=0.00..5020.00 rows=5 width=174) Filter
.........

-----------------------------------------------------------

-----------------------------------------------------------
SYSTEM:

os: Mac 10.2.4
chip: 1.4 GHz
ram: 1 GB
-----------------------------------------------------------

-----------------------------------------------------------
ERROR MESSAGE:

server process (pid 650) was terminated by signal 11
all server processes terminated; reinitializing shared memopry and
semaphores

-----------------------------------------------------------

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SOLUTIONS I HAVE TRIED

1. tweaking the five kern.sysv vars. to every configurable option possible

currently I am at:

kern.sysv.shmmax: 1073741824
kern.sysv.shmmin: 256
kern.sysv.shmmni: 8192
kern.sysv.shmseg: 2048
kern.sysv.shmall: 262144

(I know shmmin is way too high according to the stuff I read, I was just
getting desperate, I have tried just leaving it at 1)

2. lowering the number of shared_buffers and max_connections to 32:16
32:8 16:8 in postgresql.conf

currently I am at 64 shared_bufs and 32 max_connects (these were the
defaults)

3. Using the IN sql operator rather than a bunch of ORs, but I still
have the same problem

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