RE: speeding up planning with partitions

Hi David,

On Thu, Jan 10, 2019 at 4:02 PM, David Rowley wrote:
> 3. I wonder if there's a better way to handle what
> build_dummy_partition_rel() does. I see the child's relid to the
> parent's relid and makes up a fake AppendRelInfo and puts it in the
> parent's slot. What's going to happen when the parent is not the
> top-level parent? It'll already have a AppendRelInfo set.
...
>
> select * from parent p1 inner join parent p2 on p1.a=p2.a where p1.id < 10;

I think there is a mistake in the select SQL.
"p1.id < 10" doesn't prune any partition because tables are partitioned by
column "a" in your definition. Isn't it?

> Does that not mean that the if (parent->top_parent_relids) will always
> be false in build_dummy_partition_rel() and it'll only ever get
> rtekind == RTE_RELATION?

At least, I checked if (parent->top_parent_relids) can be true if I execute
below SQL.

select * from parent p1 inner join parent p2 on p1.a=p2.a where p1.id < 15;

I couldn't check other points you mentioned, but I also think
build_dummy_partition_rel() needs more consideration because I felt it has
complicated logic when I was checking around here.

Amit,
I also realized there are some mistakes in the comments around this function.

+ * build_dummy_partition_rel
+ * Build a RelOptInfo and AppendRelInfo for a pruned partition
s/and AppendRelInfo/and an AppendRelInfo/

+ * Now we'll need a (no-op) AppendRelInfo for parent, because we're
+ * setting the dummy partition's relid to be same as the parent's.
s/a \(no-op\) AppendRelInfo/an \(no-op\) AppendRelInfo/

--
Yoshikazu Imai