Re: More shared buffers causes lower performances

On Dec 26, 2007 4:41 PM, Guillaume Smet <guillaume.smet@gmail.com> wrote:
> Then I decided to perform read-only tests using -S option (pgbench -S
> -s 100 -c 16 -t 30000 -U postgres bench). And still the same
> behaviour:
> shared_buffers=64MB : 20k tps
> shared_buffers=1024MB : 8k tps

Some more information. If I strace the backends during the test, the
test is faster with shared_buffers=1024MB and I have less system calls
(less read and less lseek).

A quick cut | uniq | sort gives me:
With 64MB:
  12548 semop
 160039 sendto
 160056 recvfrom
 294289 read
 613338 lseek

With 1024MB:
  11396 semop
 129947 read
 160039 sendto
 160056 recvfrom
 449584 lseek

--
Guillaume