Horton

Re: extended stats on partitioned tables

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Jaime Casanova <jcasanov@systemguards.com.ec>, pgsql-hackers@postgresql.org
Date: 2021-11-04T02:20:56Z
Lists: pgsql-hackers

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On Thu, Nov 04, 2021 at 12:44:45AM +0100, Tomas Vondra wrote:
> > I probably did this to make the code change small, to avoid indentin the whole
> > block.
> 
> But indenting the block is not necessary. It's possible to do something
> like this:
> 
>     if (!rel->inh)
>         return 1.0;
> 
> or whatever is the "default" result for that function.

You're right.  I did like that, Except in examine_variable, which already does
it with "break".

> > Maybe the for inh<=1 loop should instead be two calls to new functions factored
> > out of get_relation_statistics() and RemoveStatisticsById(), which take "bool
> > inh".

I did like that in a separate patch for now.
And I avoided making a !inh tuple for partitioned tables, since they're never
populated.

> >> And I'm not sure we do the right thing after removing children, for example
> >> (that should drop the inheritance stats, I guess).
> > 
> > Do you mean for inheritance only ?  Or partitions too ?
> > I think for partitions, the stats should stay.
> > And for inheritence, they can stay, for consistency with partitions, and since
> > it does no harm.
> > 
> 
> I think the behavior should be the same as for data in pg_statistic,
> i.e. if we keep/remove those, we should do the same thing for extended
> statistics.

This works for column stats the way I proposed for extended stats: child stats
are never removed, neither when the only child is dropped, nor when re-running
ANALYZE (actually, that part is odd).

I can stop sending patches if it makes it hard to reconcile, but I wanted to
put it "on paper" to see/show what the patch series would look like, for v15
and back branches.

-- 
Justin

Commits

  1. Add stxdinherit flag to pg_statistic_ext_data

  2. Build inherited extended stats on partitioned tables

  3. Ignore extended statistics for inheritance trees

  4. Don't build extended statistics on inheritance trees

  5. Tighten up relation kind checks for extended statistics

  6. Avoid assuming that statistics for a parent relation reflect the properties of