Re: machine-readable explain output

Peter Eisentraut <peter_e@gmx.net> writes:
> A regression test for EXPLAIN, however, should primarily check whether the 
> output format is stable.  We are planning to offer this as a public interface, 
> after all.  You could use faked up statistics and all but one or two plan 
> types turned off, and then the results should be pretty stable.

You'd be surprised :-(.  We've found in the past that queries in the
regression tests get different plans across different platforms just
because of alignment-rule differences (leading to different numbers
of rows per page, etc etc).  I think that test cases could be chosen
to be relatively stable points in the plan space, but it's hopeless
to imagine that the low-order digits of cost estimates will be the
same across all platforms.
        regards, tom lane