Re: [Sender Address Forgery]Re: pg_(total_)relation_size andpartitioned tables

Thanks for taking a look.

On 2018/01/19 14:39, Michael Paquier wrote:
> On Thu, Jan 18, 2018 at 06:54:18PM +0900, Amit Langote wrote:
>> I think having pg_partition_root() and pg_partition_parent() will give
>> users enough to get useful views as follows:
> 
> So... pg_partition_root() gives you access to the highest relation in
> the hierarchy, and pg_partition_parent() gives you access to the direct
> parent.

Right.

>> drop table p;
>> create table p (a int) partition by list (a);
>> create table p123 partition of p for values in (1, 2, 3) partition by list
> (a);
>> create table p12 partition of p1 for values in (1, 2) partition by list (a);
>> create table p12 partition of p123 for values in (1, 2) partition by list (a);
>> create table p1 partition of p12 for values in (1);
>> create table p2 partition of p12 for values in (2);
>> create table p3 partition of p123 for values in (3);
> 
> You need to reorder those queries, the creation of the first p12 would
> fail as p1 does not exist at this point.

Oops.  I had copy-pasted above commands from the psql's \s output and
ended up copying the command I didn't intend to.  Here it is again, but
without the mistake I made in my last email:

drop table p;
create table p (a int) partition by list (a);
create table p123 partition of p for values in (1, 2, 3) partition by list
(a);
create table p12 partition of p123 for values in (1, 2) partition by list (a);
create table p1 partition of p12 for values in (1);
create table p2 partition of p12 for values in (2);
create table p3 partition of p123 for values in (3);

> Wouldn't also a
> pg_partition_tree() be useful? You could shape it as a function which
> returns all regclass partitions in the tree as unique entries. Combined
> with pg_partition_parent() it can be powerful as it returns NULL for the
> partition at the top of the tree. So I think that we could live without
> pg_partition_root(). At the end, let's design something which makes
> unnecessary the use of WITH RECURSIVE when looking at a full partition
> tree to ease the user's life.

Do you mean pg_partition_tree(regclass), that returns all partitions in
the partition tree whose root is passed as the parameter?

Perhaps, like the following (roughly implemented in the attached)?

select  pg_partition_root(p) as root_parent,
        pg_partition_parent(p) as parent,
        p as relname,
        pg_total_relation_size(p) as size
from    pg_partition_tree_tables('p') p
order by 4;
 root_parent | parent | relname |  size
-------------+--------+---------+---------
 p           |        | p       |       0
 p           | p      | p123    |       0
 p           | p123   | p12     |       0
 p           | p123   | p3      | 3653632
 p           | p12    | p1      | 3653632
 p           | p12    | p2      | 3653632
(6 rows)

> Documentation, as well as regression tests, would be welcome :)

OK, I will add those things in the next version.

Thanks,
Amit