postgres is slow??

Hi, I've written a little tcl program to test how many seconds it takes to
run an 'update' transaction and found that the running time increases by a
couple of seconds every time i run my script.

My script does the following:
-connect to postgres
-updates a row and then updates it again with some other value
-iterate the update step above 200 times
-print the number of seconds that iteration took
-disconnect from postgres

Results: So the first time, i get about 2 seconds, then 4, 6, 8... etc.

So, each time that row gets updated, the longer the next update takes...
What is happening? What do i need to do so that postgres doesn't do this?
... What do i need to do so that postgres always updates a row 200 times
in 2 seconds?

Any help would be appreciated.
Please reply to: cshum(at)cats(dot)ucsc(dot)edu