Re: get_actual_variable_range vs idx_scan/idx_tup_fetch

Marko Tiikkaja <marko@joh.to> writes:
> This week we had one of the most annoying problems I've ever encountered 
> with postgres.  We had a big index on multiple columns, say,  foo(a, b, 
> c).  According to pg_stat_all_indexes the index was being used *all the 
> time*.  However, after looking into our queries more closely, it turns 
> out that it was only being used to look up statistics for the foo.a 
> column to estimate merge scan viability during planning.  But this took 
> hours for two people to track down.

> So what I'd like to have is a way to be able to distinguish between 
> indexes being used to answer queries, and ones being only used for stats 
> lookups during planning.

Why?  Used is used.
        regards, tom lane