Postgres is using 100% CPU

Hi All,

I am using postgresDB on redhat machine which is having 4GB RAM
machine. As soon as it starts to update the postgres DB it will reach
100%cpu. It will comedown to normal after 40 minutes. I tried perform
some tuning on the postgres DB, But result was same.I am not postgres
DB expert. Even we are not seeing in all machine. Only few machines we
are seeing this issue. Any help on this would be appreciated.

Thanks,
Ashik