Re: expanding inheritance in partition bound order

On 16 August 2017 at 11:06, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:

> Attached updated patches.

Thanks Amit for the patches.

I too agree with the overall approach taken for keeping the locking
order consistent: it's best to do the locking with the existing
find_all_inheritors() since it is much cheaper than to lock them in
partition-bound order, the later being expensive since it requires
opening partitioned tables.

> I haven't yet done anything about changing the timing of opening and
> locking leaf partitions, because it will require some more thinking about
> the required planner changes. But the above set of patches will get us
> far enough to get leaf partition sub-plans appear in the partition bound
> order (same order as what partition tuple-routing uses in the executor).

So, I believe none of the changes done in pg_inherits.c are essential
for expanding the inheritence tree in bound order, right ? I am not
sure whether we are planning to commit these two things together or
incrementally :
1. Expand in bound order
2. Allow for locking only the partitioned tables first.

For #1, the changes in pg_inherits.c are not required (viz, keeping
partitioned tables at the head of the list, adding inhchildparted
column, etc).

If we are going to do #2 together with #1, then in the patch set there
is no one using the capability introduced by #2. That is, there are no
callers of find_all_inheritors() that make use of the new
num_partitioned_children parameter. Also, there is no boolean
parameter for find_all_inheritors() to be used to lock only the
partitioned tables.

I feel we should think about
0002-Teach-pg_inherits.c-a-bit-about-partitioning.patch later, and
first get the review done for the other patches.

-------

I see that RelationGetPartitionDispatchInfo() now returns quite a
small subset of what it used to return, which is good. But I feel for
expand_inherited_rtentry(), RelationGetPartitionDispatchInfo() is
still a bit heavy. We only require the oids, so the
PartitionedTableInfo data structure (including the pd->indexes array)
gets discarded.

Also, RelationGetPartitionDispatchInfo() has to call get_rel_relkind()
for each child. In expand_inherited_rtentry(), we anyway have to open
all the child tables, so we get the partition descriptors for each of
the children for free. So how about, in expand_inherited_rtentry(), we
traverse the partition tree using these descriptors similar to how it
is traversed in RelationGetPartitionDispatchInfo() ? May be to avoid
code duplication for traversing, we can have a common API.

Still looking at RelationGetPartitionDispatchInfo() changes ...

--
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company