"Yinan Li" <yinanli@cse.ust.hk> writes:
> When I use the statistics collector to see the number of IO, I always get
> zero in almost all of columns. I really want to know the reason for that.
It sure sounds like you don't really have stats_block_level turned on.
Did you remember to SIGHUP the postmaster after editing the
configuration file?
regards, tom lane