Re: [HACKERS] expanding inheritance in partition bound order

On Thu, Aug 31, 2017 at 1:15 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Aug 30, 2017 at 12:47 PM, Ashutosh Bapat
> <ashutosh.bapat@enterprisedb.com> wrote:
>> +1. I think we should just pull out the OIDs from partition descriptor.
>
> Like this?  The first patch refactors the expansion of a single child
> out into a separate function, and the second patch implements EIBO on
> top of it.
>
> I realized while doing this that we really want to expand the
> partitioning hierarchy depth-first, not breadth-first.  For some
> things, like partition-wise join in the case where all bounds match
> exactly, we really only need a *predictable* ordering that will be the
> same for two equi-partitioned table.

+1. Spotted right!

> A breadth-first expansion will
> give us that.  But it's not actually in bound order.  For example:
>
> create table foo (a int, b text) partition by list (a);
> create table foo1 partition of foo for values in (2);
> create table foo2 partition of foo for values in (1) partition by range (b);
> create table foo2a partition of foo2 for values from ('b') to ('c');
> create table foo2b partition of foo2 for values from ('a') to ('b');
> create table foo3 partition of foo for values in (3);
>
> The correct bound-order expansion of this is foo2b - foo2a - foo1 -
> foo3, which is indeed what you get with the attached patch.  But if we
> did the expansion in breadth-first fashion, we'd get foo1 - foo3 -
> foo2a, foo2b, which is, well, not in bound order.  If the idea is that
> you see a > 2 and rule out all partitions that appear before the first
> one with an a-value >= 2, it's not going to work.

Here are the patches revised a bit. I have esp changed the variable
names and arguments to reflect their true role in the functions. Also
updated prologue of expand_single_inheritance_child() to mention
"has_child". Let me know if those changes look good.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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