Re: vacuumdb changes for stats import/export

>
>
> >
> > Statistics are transactional.  Without this option specified are we
> really
> > removing them and commiting prior to computing and saving new ones?  And
> we are
> > opposed to just changing this behavior and instead prefer to add an
> option that
> > at first glance seems like everyone should use?
>
> Yes, I thought it was transactional too, but the doc patch suggests is
> isn't, so maybe I am wrong.
>

It is transactional, mostly.

The attribute stats for the table being analyzed and all attribute stats
for the dependent indexes that have at least one expression column, plus
extended stats objects on that table, will be replaced in one atomic
operation. The old stats were there, commit happens, now the new stats are
there.

The relation stats (pg_class) happen in-place, non-transactionally. So if
you had an analyze that got canceled, and some of the relstats had been
updated on the table or indexes, those would stay as-is.

Having said all that, these are very nitpick details that may not need to
be in our documentation.


>
> > "If not specified the system will analyze all statistics-capable objects
> in
> > alphabetical order.  Specifying this option then limits the result to
> only
> > those objects that do not already have statistics.". That may not be how
> the
> > feature strictly behaves but that would seem to be all one would expect
> it to
> > do.
>

/me dons Hat of Pedantry (+2 against simple explanations)

"Specifying this option then limits the result to only tables that are
missing an attribute statistic, have an index that is missing an attribute
statistic, or have an extended statistics object that is itself missing
object statistics".

/me removes hat

"Specifying this option then limits the result to only those tables that do
not already have complete statistics."

The above phrase is asking the word "complete" to do a lot of heavy
lifting, covering the dependent indexes and extended statistics objects.
Specifying "table" makes it clear that any deficit in statistics results in
the table getting analyzed, not just the single index or extended object.