Re: Partition-wise join for join between (declaratively) partitioned tables

On Tue, Oct 3, 2017 at 7:48 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Sep 21, 2017 at 8:21 AM, Ashutosh Bapat
> <ashutosh.bapat@enterprisedb.com> wrote:
>> Here's set of rebased patches. The patch with extra tests is not for
>> committing. All other patches, except the last one, will need to be
>> committed together. The last patch may be committed along with other
>> patches or as a separate patch.
>
> In set_append_rel_size, is it necessary to set attr_needed =
> bms_copy(rel->attr_needed[index]) rather than just pointing to the
> existing value?  If so, perhaps the comments should explain the
> reasons.  I would have thought that the values wouldn't change after
> this point, in which case it might not be necessary to copy them.

Right. The only places where attr_needed is changed is in
remove_rel_from_query() (useless join removal) and
add_vars_to_targetlist(). Both of those happen before
set_append_rel_size(). Since parent and child join should project same
attributes, having them share the Relids set makes more sense. So,
changed accordingly and explained the same in comments.

Also, changed list_nth() in the following code block to use list_nth_node().

>
> Regarding nomenclature and my previous griping about wisdom, I was
> wondering about just calling this a "partition join" like you have in
> the regression test.  So the GUC would be enable_partition_join, you'd
> have generate_partition_join_paths(), etc.  Basically just delete
> "wise" throughout.

Partition-wise join is standard term used in literature and in
documentation of other popular DBMSes, so partition_wise makes more
sense. But I am fine with partition_join as well. Do you want it
partition_join or partitionjoin like enable_mergejoin/enable_hashjoin
etc.?

>
> The elog(DEBUG3) in try_partition_wise_join() doesn't follow message
> style guidelines and I think should just be removed.  It was useful
> for development, I'm sure, but it's time for it to go.

Done.

>
> +            elog(ERROR, "unrecognized path node type %d", (int) nodeTag(path));
>
> I think we should use the same formulation as elsewhere, namely
> "unrecognized node type: %d".  And likewise probably "unexpected join
> type: %d".

Changed "unrecognized path node type" to "unrecognized node type".

 "unrecognized join type: %d" seems to be used everywhere except
postgres_fdw. So, used that. Also added a cast to int similar to other
places.

>
> partition_join_extras.sql has a bunch of whitespace damage, although
> it doesn't really matter since, as you say, that's not for commit.
>

Right. I will remove that patch from the patch-set when those tests
are no more needed i.e. once we are done with code changes to the
patches.

Attached the updated patch-set.

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