Re: Collect frequency statistics for arrays

On Thu, Mar 1, 2012 at 1:09 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

That seems like a pretty narrow, uncommon use-case.  Also, to get

accurate stats for such queries that way, you'd need really enormous
histograms.  I doubt that the existing parameters for histogram size
will permit meaningful estimation of more than the first array entry
(since we don't make the histogram any larger than we do for a scalar
column).

The real point here is that the fact that we're storing btree-style
stats for arrays is an accident, backed into by having added btree
comparators for arrays plus analyze.c's habit of applying default
scalar-oriented analysis functions to any type without an explicit
typanalyze entry.  I don't recall that we ever thought hard about
it or showed that those stats were worth anything.

OK. I don't object to removing btree stats from arrays.

What do you thinks about pg_stats view in this case? Should it combine values histogram and array length histogram in single column like do for MCV and MCELEM?