"Gurjeet Singh" <singh.gurjeet@gmail.com> writes:
> During these spikes, in the 'top' sessions we see the 'idle' PG
> processes consuming between 2 and 5 % CPU, and since the box has 8 CPUS (2
> sockets and each CPU is a quad core Intel Xeon processors) and somewhere
> around 200 Postgres processes, the load spikes to above 200; and it does
> this very sharply.
This looks like heavy contention for a spinlock. You need to get a
higher-level analysis of what's happening before anyone can say much
more than that.
Note that 8.1 is pretty much ancient history as far as scalability to
8-core hardware goes. You should probably consider updating to 8.3
before investing too much time in tracking down what's happening.
If you can still show the problem on 8.3 then there would be some
interest in fixing it ...
regards, tom lane