Re: Forcing Postgres to Execute a Specific Plan

All paths of optimizer are just in function "standard_planner", which mainly
calls "subquery_planner", which just takes the rewrited structure "Query" as
the main parameter. But system provides another way if you wannt to write
your own optimizer, that is: define the global var "planner_hook" to your
own optimizer function (please refer to function "planner"). So this is one
of the way prevents the system takes it own optimizer routine.

If you want to modify the plan returned by the optimizer, you can add some
code just in the function "planner", i.e., takes result as the param of your
routine.

Any way, It is needed that you get very familiar with the structure of
"PlannedStmt".

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2008/6/3 John Cieslewicz <johnc(at)cs(dot)columbia(dot)edu>:
I completely understand that what I am proposing is somewhat mad and I
didn't expect it to be easy.

Basically, I'm doing some research on a new operator and would like to start
testing it by inserting it into a very specific place in very specific plans
without having to do too much work in plan generation or optimization. I
think that I could do this by writing some code to inspect a plan and swap
out the piece that I care about. I realize this is a hack, but at the moment
it's just for research purposes. Though I have worked with the internals of
other db systems, I'm still getting familiar with postgres. Could such a
piece of code be placed in the optimizer just before it returns an optimized
plan or can a plan be modified after it is returned by the optimizer?

John Cieslewicz.