how to debug the postgres performance issue

Hi,

We are doing the performance test in two nodes system(active/standby). Now we find that the disk IO is very high but the CPU is low. Is there any method or tool to help us debug to find which function makes this issue?

We try to use the gprof but it does not help us. The result show the LWLockAssign（the shared buffer init） is called the most time. The other function is called no more that 33139. That seems no problem.

Could you please give any suggestion how to debug the high IO/low CPU issue?

Thanks
Steven

===================================
no time accumulated

% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 9240928 0.00 0.00 LWLockAssign
0.00 0.00 0.00 33139 0.00 0.00 ShmemAlloc
0.00 0.00 0.00 33084 0.00 0.00 seg_alloc
….