Tom Lane wrote:
Not too many releases ago, there were several columns in pg_proc that
were intended to support estimation of the runtime cost and number of
result rows of set-returning functions.  I believe in fact that these
were the remains of Joe Hellerstein's thesis on expensive-function
evaluation


FYI, Hellerstein's thesis on xfunc optimization is available here:

    ftp://ftp.cs.wisc.edu/pub/tech-reports/reports/1996/tr1304.ps.Z

There's also a paper on this subject by Hellerstein that was published in Transactions on Database Systems:

    http://www.cs.berkeley.edu/~jmh/miscpapers/todsxfunc.pdf

I haven't had a chance to digest either one yet, but it might be worth a look.

-Neil

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