Re: Adding support for Default partition in partitioning

On Wed, Jun 7, 2017 at 2:08 AM, Jeevan Ladhe
<jeevan(dot)ladhe(at)enterprisedb(dot)com> wrote:
[...]
>>
>> The code in check_default_allows_bound() to check whether the default
>> partition
>> has any rows that would fit new partition looks quite similar to the code
>> in
>> ATExecAttachPartition() checking whether all rows in the table being
>> attached
>> as a partition fit the partition bounds. One thing that
>> check_default_allows_bound() misses is, if there's already a constraint on
>> the
>> default partition refutes the partition constraint on the new partition,
>> we can
>> skip the scan of the default partition since it can not have rows that
>> would
>> fit the new partition. ATExecAttachPartition() has code to deal with a
>> similar
>> case i.e. the table being attached has a constraint which implies the
>> partition
>> constraint. There may be more cases which check_default_allows_bound()
>> does not
>> handle but ATExecAttachPartition() handles. So, I am wondering whether
>> it's
>> better to somehow take out the common code into a function and use it. We
>> will
>> have to deal with a difference through. The first one would throw an error
>> when
>> finding a row that satisfies partition constraints whereas the second one
>> would
>> throw an error when it doesn't find such a row. But this difference can be
>> handled through a flag or by negating the constraint. This would also take
>> care
>> of Amit Langote's complaint about foreign partitions. There's also another
>> difference that the ATExecAttachPartition() queues the table for scan and
>> the
>> actual scan takes place in ATRewriteTable(), but there is not such queue
>> while
>> creating a table as a partition. But we should check if we can reuse the
>> code to
>> scan the heap for checking a constraint.
>>
>> In case of ATTACH PARTITION, probably we should schedule scan of default
>> partition in the alter table's work queue like what
>> ATExecAttachPartition() is
>> doing for the table being attached. That would fit in the way alter table
>> works.
>
>
> I am still working on this.
> But, about your comment here:
> "if there's already a constraint on the default partition refutes the
> partition
> constraint on the new partition, we can skip the scan":
> I am so far not able to imagine such a case, since default partition
> constraint
> can be imagined something like "minus infinity to positive infinity with
> some finite set elimination", and any new non-default partition being added
> would simply be a set of finite values(at-least in case of list, but I think
> range
> should not also differ here). Hence one cannot imply the other here.
> Possibly,
> I might be missing something that you had visioned when you raised the flag,
> please correct me if I am missing something.
>

IIUC, default partition constraints is simply NOT IN (<values of all
other sibling partitions>).
If constraint on the default partition refutes the new partition's
constraints that means we have overlapping partition, and perhaps
error.

Regards,
Amul