Re: WIP: Upper planner pathification

Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
>> I do not think the patch will make a lot of performance difference as-is;
>> its value is more in what it will let us do later. There are a couple of

> Yep, for now on my notebook (best from 5 tries):
> % pgbench -i -s 3000
> % pgbench -s 3000 -c 4 -j 4 -P 1 -T 60
> HEAD 569 tps
> patched 542 tps
> % pgbench -s 3000 -c 4 -j 4 -P 1 -T 60 -S
> HEAD 9500 tps
> patched 9458 tps

> Looks close to measurement error, but may be explained increased amount of work
> for planning. Including, may be, more complicated path tree.

I think the default pgbench queries are too simple to have any possible
benefit from this patch. It does look like you're seeing some extra
planning time, which I think is likely due to redundant construction
of PathTargets. The new function set_pathtarget_cost_width() is not
very cheap, and in order to minimize the delta in this patch I did
not worry much about avoiding duplicate calls of it. That's another
thing in a long list of things to do later ;-). There might be other
pain points I haven't recognized yet.

regards, tom lane