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

On Mon, Feb 6, 2017 at 3:34 PM, Ashutosh Bapat
<ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> PartitionScheme is shared across multiple relations, join or base,
> partitioned similarly. Obviously it can't and does not need to point
> partition bound informations (which should all be same) of all those
> base relations. O the the face of it, it looks weird that it points to
> only one of them, mostly the one which it encounters first. But, since
> it's going to be the same partition bound information, it doesn't
> matter which one. So, I think, we can point of any one of those. Do
> you agree?

Yes.

>> The fact that set_append_rel_size needs to reopen the relation to
>> extract a few more bits of information is not desirable. You need to
>> fish this information through in some other way; for example, you
>> could have get_relation_info() stash the needed bits in the
>> RelOptInfo.
>
> I considered this option and discarded it, since not all partitioned
> relations will have OIDs for partitions e.g. partitioned joins will
> not have OIDs for their partitions. But now that I think of it, we
> should probably store those OIDs just for the base relation and leave
> them unused for non-base relations just like other base relation
> specific fields in RelOptInfo.

Right.

>> FRACTION_PARTS_TO_PLAN seems like it should be a GUC.
>
> +1. Will take care of this. Does "representative_partitions_fraction"
> or "sample_partition_fraction" look like a good GUC name? Any other
> suggestions?

I like the second one.

--
Robert Haas
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