Re: function calls optimization

I recently implemented something closely related to this.  Combining and
migrating expensive STABLE user-defined functions to the FROM clause, where
the function is evaluated as a lateral join (or "cross apply").  I'm
defining expensive as 50x times more expensive than the default function
cost.

For functions that return multiple outputs and where the query uses (...).*
notation, this will, for example, consolidate all of the calls in the *
expansion into a single call.  It also looks in the WHERE clause and HAVING
clause, and combines those references, too.  Currently it requires the
function to be in a top-level AND condition, if it appears in a predicate.

I think I can get permission for contributing it back.  If there's an
interest in it, let me know.



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Jim Finnerty, AWS, Amazon Aurora PostgreSQL
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