Found it!
include/config.h.in
#define INDEX_MAX_KEYS 8
----- Original Message -----
From: "Thomas Lockhart" <lockhart@alumni.caltech.edu>
To: "Grigori Soloviov" <grisha@iqchoice.com>
Sent: Thursday, July 06, 2000 6:30 PM
Subject: Re: [HACKERS] pl/pgsql function out parameters
> > Don't you know how to make it take more than 8 parameters?
>
> In the current development tree, the limit is higher than 8 parameters.
> My recollection is that in earlier code the "8 parameter limit" is
> fairly difficult to work around. Not sure if 7.0 makes it easier; look
> for a hardcoded #define in include/config.h.
>
> - Thomas
>