Query timing stable?

Hi,

I turned on "\timing" in the command line. It seems that the timing is
not stable. For the same query, the query's executing time is longer for
the first time I run it than for the second and third time run it. I
think it might be "cached" automatically.

Is there a way to turn the "automatic caching" off so that I can get the
same "timing" when I run the same query? Or is there some other way to
get stable query time whenever the query is run?

Thanks,
Cheng