Re: 8.3devel slower than 8.2 under read-only load

Greg Smith <gsmith(at)gregsmith(dot)com> writes:
> On Wed, 21 Nov 2007, Guillaume Smet wrote:
>> *** 8.2 ***
>> tps = 853.360277 (including connections establishing)
>>
>> *** 8.3 ***
>> tps = 784.819087 (including connections establishing)

> This is an 8% drop. I've seen a larger difference than that between two
> identical installations of the same version when the database is many GB
> large. Hard drives deliver a higher transfer rate at their inner
> portions, typically the start of the disk from the operating system's
> perspective. It's not unusual for the slow parts of the disk to be 30-40%
> slower than the fast ones.

FWIW, the test cases I was just comparing are entirely CPU-bound ---
vmstat says there are no disk reads happening at all. Now I only got a
3% drop, so that may not be the same effect Guillaume is seeing. But
the whole thing is a bit upsetting seeing that we thought we'd reduced
the overhead for short read-only transactions ...

regards, tom lane