Re: [HACKERS] Optimise default partition scanning while adding newpartition

On 2017/09/16 1:57, Amit Langote wrote:
> On Sat, Sep 16, 2017 at 12:59 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> I believe the intended advantage of the current system is that if you
>> specify multiple operations in a single ALTER TABLE command, you only
>> do one scan rather than having a second scan per operation.  If that's
>> currently working, we probably don't want to make it stop working.
> 
> OK.
> 
> How about squash Jeevan's and my patch, so both
> check_default_allows_bound() and ValidatePartitionConstraints() know
> to scan default partition's children and there won't be any surprises
> in the regression test output as you found after applying just the
> Jeevan's patch.  Unfortunately, I'm not able to post such a patch
> right now.

I guess we don't need to squash, as they could be seen as implementing
different features. Reordering the patches helps though.  So, apply them
in this order:

1. My patch to teach ValidatePartitionConstraints() to skip scanning
   a partition's own partitions, which optimizes ATTACH PARTITION
   command's partition constraint validation scan (this also covers the
   case of scanning the default partition to validate its updated
   constraint when attaching a new partition)

2. Jeevan's patch to teach check_default_allows_bound() to skip scanning
   the default partition's own partitions, which covers the case of
   scanning the default partition to validate its updated constraint when
   adding a new partition using CREATE TABLE

Attached 0001 and 0002 are ordered that way.

In addition to implementing the features mentioned in 1 and 2 above, the
patches also modify the INFO message to mention "updated partition
constraint for default partition \"%s\"", instead of "partition constraint
for table \"%s\"", when the default partition is involved.  That's so that
it's consistent with the error message that would be emitted by either
check_default_allows_bound() or ATRewriteTable() when the scan finds a row
that violates updated default partition constraint, viz. the following:
"updated partition constraint for default partition \"%s\" would be
violated by some row"

Thoughts?

Thanks,
Amit

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