Re: Statistics Import and Export

Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> We need to get the original element type on the import side somehow,
> right? Otherwise it will be hard to tell whether '{1, 2, 3, 4}' has
> element type "int4" or "text", which affects the binary representation
> of the anyarray value in pg_statistic.

Yeah, but that problem exists no matter what. I haven't read enough
of the patch to find where it's determining that, but I assume there's
code in there to intuit the statistics storage type depending on the
table column's data type and the statistics kind.

> Either we need to get it at export time (which seems the most reliable
> in principle, but problematic for older versions) and pass it as an
> argument to pg_set_attribute_stats(); or we need to derive it reliably
> from the table schema on the destination side, right?

We could not trust the exporting side to tell us the correct answer;
for one reason, it might be different across different releases.
So "derive it reliably on the destination" is really the only option.

I think that it's impossible to do this in the general case, since
type-specific typanalyze functions can store pretty nearly whatever
they like. However, the pg_stats view isn't going to show nonstandard
statistics kinds anyway, so we are going to be lossy for custom
statistics kinds.

regards, tom lane