I will try to reduce shared buffer to 1536 [1.87 Mb].

1536 is probaby too low. I've tested a bunch of different settings on my 8GB Opteron server and 10K seems to be the best setting.

also effective cache is the sum of kernel buffers + shared_buffers so it
should be bigger than shared buffers.

also make the effective cache to 2097152 [2 Gb]. I will give you the result , because tomorrow [4/12/05] will be the official day of my hospital [which have more than 1700 OPD patient/day].

To figure out your effective cache size, run top and add free+cached.

Also turning hyperthreading off may help, it is unlikely it is doing any
good unless you are running a relatively new (2.6.x) kernel.

Why , could you give me the reason?

Pre 2.6, the kernel does not know the difference between logical and physical CPUs. Hence, in a dual processor system with hyperthreading, it actually sees 4 CPUs. And when assigning processes to CPUs, it may assign to 2 logical CPUs in the same physical CPU.

I presume you are vacuuming on a regular basis?

Yes , vacuumdb daily.

Do you vacuum table by table or the entire DB? I find over time, the system tables can get very bloated and cause a lot of slowdowns just due to schema queries/updates. You might want to try a VACUUM FULL ANALYZE just on the system tables.

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