Re: Statistics Import and Export

All the C code changes make sense to me. Though as an aside, we're going to run into the parameter-ordering problem when it comes to pg_clear_attribute_stats, but that's a (read: my) problem for a later patch.

Documentation:

+         The currently-supported relation statistics are
+         <literal>relpages</literal> with a value of type
+         <type>integer</type>, <literal>reltuples</literal> with a value of
+         type <type>real</type>, and <literal>relallvisible</literal> with a
+         value of type <type>integer</type>.

Could we make this a bullet-list? Same for the required attribute stats and optional attribute stats. I think it would be more eye-catching and useful to people skimming to recall the name of a parameter, which is probably what most people will do after they've read it once to get the core concepts.


Question:

Do we want to re-compact the oids we consumed in pg_proc.dat?


Test cases:

We're ripping out a lot of regression tests here. Some of them obviously have no possible pg_restore_* analogs, such as explicitly set NULL values vs omitting the param entirely, but some others may not, especially the ones that test required arg-pairs.

Specifically missing are:

* regclass not found
* attribute is system column
* scalars can't have mcelem
* mcelem / mcelem freqs mismatch (parts 1 and 2)
* scalars can't have elem_count_histogram

* cannot set most_common_elems for range type
 
I'm less worried about all the tests of successful import calls, as the pg_upgrade TAP tests kick those tires pretty well.

I'm also ok with losing the copies from test to test_clone, those are also covered well by the TAP tests.

I'd feel better if we adapted the above tests from set-tests to restore-tests, as the TAP suite doesn't really cover intentionally bad stats.