Shared memory seems not in use

Hi Guys,

I would really appreciate if someone could bring the light to this. Thank
you in advance. Here's my story:

postgresql-7.4.6
Linux Red Hat 9.0

I'm trying as anyone who ever installed Postgresql optimize it for speed.
After reading all those articles about increasing shared memory and tweaking
other params in postgesql.conf I ended up with :

Making 96MB shmax in Linux total
Making 96MB shmall in Linux total

Setting 8000 * 8 KB each for shared buffers in postgres conf
Setting sort_memory to 1024
Setting effective cache to 8MB in postgres conf
Decreasing connections number to 64
Checking Indexes in database scheme

And it did not seem affect in any way speed. The most confusing thing to me
that if I run Linux 'free' command it shows for shared memory usage 0bytes.
How it could come so? Here are my outputs:

[root(at)ns bin]# free
total used free shared buffers cached
Mem: 481268 473480 7788 0 117628 67424
-/+ buffers/cache: 288428 192840
Swap: 979956 889040 90916

[root(at)ns bin]# ipcs

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 2654208 postgres 600 67960832 6
0x00000000 32769 root 600 92164 10 dest
0x00000000 2228226 root 600 524288 21 dest

------ Semaphore Arrays --------
key semid owner perms nsems
0x0052e2c1 25329664 postgres 600 17
0x0052e2c2 25362433 postgres 600 17
0x0052e2c3 25395202 postgres 600 17
0x00000000 5439491 apache 600 1
0x00000000 5472260 apache 600 1
0x00000000 5505029 apache 600 1
0x00000000 6029318 apache 600 1
0x00000000 6062087 apache 600 1
0x00000000 6094856 apache 600 1
0x00000000 12353545 apache 600 1
0x00000000 12386314 apache 600 1
0x00000000 12419083 apache 600 1
0x00000000 12779532 apache 600 1
0x00000000 12812301 apache 600 1
0x00000000 12845070 apache 600 1
0x00000000 17858575 apache 600 1
0x00000000 17891344 apache 600 1
0x00000000 17924113 apache 600 1
0x0052e2c4 25427986 postgres 600 17
0x0052e2c5 25460755 postgres 600 17
0x00000000 18972694 apache 600 1
0x00000000 19005463 apache 600 1
0x00000000 19038232 apache 600 1
0x00000000 19300377 apache 600 1
0x00000000 19333146 apache 600 1
0x00000000 19365915 apache 600 1
0x00000000 19955740 apache 600 1
0x00000000 19988509 apache 600 1
0x00000000 20021278 apache 600 1
0x00000000 21102623 apache 600 1
0x00000000 21135392 apache 600 1
0x00000000 21168161 apache 600 1
0x00000000 23035938 apache 600 1
0x00000000 23068707 apache 600 1
0x00000000 23101476 apache 600 1
0x00000000 24346661 apache 600 1
0x00000000 24379430 apache 600 1
0x00000000 24412199 apache 600 1
0x00000000 24510504 apache 600 1
0x00000000 24543273 apache 600 1
0x00000000 24576042 apache 600 1
0x00000000 24838187 apache 600 1
0x00000000 24870956 apache 600 1
0x00000000 24903725 apache 600 1

------ Message Queues --------
key msqid owner perms used-bytes messages

Michael.