Hi,

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. Perhaps the easiest way would be adding a new column or two into pg_stat_all_indexes, which we would increment in get_actual_variable_range() when fetching data.

Any thoughts?


.marko


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