Postmaster taking up 100% of CPU

Hi,everyone

The CPU of my linux box is 100% by postmaster processes for hours.
How to deal with it?
The following is my top log and ps log:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 8970 postgres  16   0 53692  36m  34m R 27.3  3.6   1:14.80 postmaster
 8807 postgres  16   0 53696  36m  34m R 27.0  3.6   1:26.62 postmaster
 8653 postgres  16   0 53696  36m  34m R 23.7  3.6   1:32.29 postmaster
 8961 postgres  16   0 53692  36m  34m R 21.7  3.6   1:36.59 postmaster