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Re: Function Stats WAS: Passing arguments to views

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Function Stats WAS: Passing arguments to views
Date: 2006-02-03 19:49:06
Message-ID: 200602031149.07079.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom,

> > What I'd like to do is implement the constant method for 8.2, and work
> > on doing the S() method later on.  Does that make sense?
>
> I'm not thrilled with putting in a stopgap that we will have to support
> forever.  The constant method is *clearly* inadequate for many (probably
> most IMHO) practical cases.  Where do you see it being of use?

Well, mostly for the real-world use cases where I've run into SRF estimate 
issues, which have mostly been SRFs which return one row.

> W.R.T. the estimator function method, the concern about recursion seems
> misplaced.  Such an estimator presumably wouldn't invoke the associated
> function itself.  

No, but if you're calling the S() estimator in the context of performing a 
join, what do you supply for parameters?

> I'm more concerned about coming up with a usable API 
> for such things.  Our existing mechanisms for estimating operator
> selectivities require access to internal planner data structures, which
> makes it pretty much impossible to write them in anything but C.  We'd
> need something cleaner to have a feature I'd want to export for general
> use.

Yes -- we need to support the simplest case, which is functions that return 
either (a) a fixed number of rows, or (b) a fixed multiple of the number 
of rows passed to the function.  These simple cases should be easy to 
build.  For more complex estimation, I personally don't see a problem with 
forcing people to hack it in C.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

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