That is it possible to tell the planner that index is off limits i.e. don't
ever generate a plan using it?

Rationale:  Schema changes on big tables.  I might have convinced myself /
strong beliefs that for all queries that I need to be fast the planner does
not need to use a given index (e.g. other possible plans are fast enough).
However if I just drop the index and it turns out I'm wrong I might be in a
world of pain because it might just take way to long to recreate the index.

I know that I can use pg_stat* to figure out if an index is used at all.
But in the presense of multiple indices and complex queries the planner
might prefer the index-to-be-dropped but the difference to the alternatives
available is immaterial.

The current best alternative we have is to test such changes on a testing
database that gets regularly restored from production.  However at least in
our case we simply don't know all possible queries (and logging all of them
is not an option).



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