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

"Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com> writes:
> On Nov 22, 2007 6:44 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Are you examining only "trivial" queries? I've been able to identify a
>> couple of new planner hotspots that could explain some slowdown if the
>> planning time is material compared to the execution time. If you're
>> seeing a slowdown on queries that run for awhile, that would be
>> something else ...

> Yes, I kept only queries with no join and a couple of where
> conditions. As I explained previously, I can reproduce the behavior
> with a single index scan on only one table (plan posted previously).
> If anyone is interested I can post the content of this table (there's
> nothing confidential in it so I should have the customer permission)
> and a couple of instructions to reproduce the test case.

I don't think you need to --- the "read-only transaction" case built
into pgbench is probably an equivalent test. What it looks like to
me is that the EquivalenceClass mechanism has added a little bit of
overhead, which isn't actually buying much of anything in these
trivial cases. I'll look at whether it can be short-circuited.

regards, tom lane