> In this example, hashing the large table is actually 2 seconds *faster*
> than hashing the small table (again, all on my laptop).
Are you running the laptop on battery? When I've benchmarked pgsql last
time I used my laptop as well and it only occured to me after a lot of
trying that laptops (even with all energy saving disabled in my case)
don't always make for reliable benchmark machines. Things like your CPU
clockspeed being dynamically adjusted can produce really strange results.
Also when I was running on battery the performance numbers could not be
compared in any way to when I was running with the laptop connected
straight to a socket. Things like IO/CPU ratio were completely different.
And numbers on the final testing servers were even different.
Of course your test case might not be affected by this at all, but it's
something to watch out for.
-Matthias