Re: [HACKERS] Relpartbound, toasting and pg_class

On 2017-06-12 19:00:02 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2017-06-12 18:10:52 -0400, Tom Lane wrote:
> >> it'd be worthwhile checking some actual examples rather than guessing.
> 
> > It's indeed not very compact.  E.g a simple example with small types:
> 
> > CREATE TABLE partitioned(a int, b int, c timestamptz, data text) PARTITION BY RANGE (a, b, c);
> > CREATE TABLE partitioned_child1 PARTITION OF partitioned FOR VALUES FROM (1, 1, '2017-01-01') TO (1, 1,
'2017-02-01');
> 
> > postgres[6961][1]=# SELECT relname, pg_column_size(relpartbound), length(relpartbound), pg_column_size(pg_class)
FROMpg_class WHERE relpartbound IS NOT NULL;
 
> > ┌───────────────────────────────┬────────────────┬────────┬────────────────┐
> > │            relname            │ pg_column_size │ length │ pg_column_size │
> > ├───────────────────────────────┼────────────────┼────────┼────────────────┤
> > │ partitioned_child1            │           1355 │   1351 │           1523 │
> > │ partitioneded_list_committers │           1130 │   8049 │           1298 │
> > └───────────────────────────────┴────────────────┴────────┴────────────────┘
> 
> So, counting on my fingers, you'd need something like twenty partitioning
> columns before you hit trouble with the RANGE syntax.

Well, that's with 4/8 byte wide types.  I'd be surprised if people only
ever used those.  I'd bet quite a bit that people will start using
jsonb, postgis' geometry and such as partition types, even if it makes
most of us cringe.


> On the whole, I'm inclined to agree with Peter and Alvaro that this is
> fine, at least for the short term.  Even in the long term, I doubt we
> need toastability, just a more compact representation than an expression
> tree.  bytea storage of an array, perhaps?  Or maybe better, use anyarray
> like we do in pg_statistic, so that it prints legibly.

I'm not quite sure where the aversion to adding a toast table to
pg_class is coming from?  Why are we ok with arbitrary and hard to
understand restrictions here, and not elsewhere?

Greetings,

Andres Freund