Re: [HACKERS] Declarative partitioning - another take - Mailing list pgsql-hackers

On 2017/01/20 4:18, Robert Haas wrote:
> On Thu, Jan 19, 2017 at 12:15 AM, Amit Langote wrote:
>> 0002-Set-ecxt_scantuple-correctly-for-tuple-routing.patch
>>
>> In 2ac3ef7a01df859c62d0a02333b646d65eaec5ff, we changed things so that
>> it's possible for a different TupleTableSlot to be used for partitioned
>> tables at successively lower levels.  If we do end up changing the slot
>> from the original, we must update ecxt_scantuple to point to the new one
>> for partition key of the tuple to be computed correctly.
>>
>> Last posted here:
>> https://www.postgresql.org/message-id/99fbfad6-b89b-9427-a6ca-197aad98c48e%40lab.ntt.co.jp
> 
> Why does FormPartitionKeyDatum need this?  Could that be documented in
> a comment in here someplace, perhaps the header comment to
> FormPartitionKeyDatum?

FormPartitionKeyDatum() computes partition key expressions (if any) and
the expression evaluation machinery expects ecxt_scantuple to point to the
tuple to extract attribute values from.

FormPartitionKeyDatum() already has a tiny comment, which it seems is the
only thing we could say here about this there:

* the ecxt_scantuple slot of estate's per-tuple expr context must point to
* the heap tuple passed in.

In get_partition_for_tuple() which calls FormPartitionKeyDatum(), the
patch adds this comment (changed it a little from the last version):

+ /*
+  * Extract partition key from tuple. Expression evaluation machinery
+  * that FormPartitionKeyDatum() invokes expects ecxt_scantuple to
+  * point to the correct tuple slot.  The slot might have changed from
+  * what was used for the parent table if the table of the current
+  * partitioning level has different tuple descriptor from the parent.
+  * So update ecxt_scantuple accordingly.
+  */
+ ecxt->ecxt_scantuple = slot;
FormPartitionKeyDatum(parent, slot, estate, values, isnull);

It says why we need to change which slot ecxt_scantuple points to.

>> 0004-Fix-some-issues-with-views-and-partitioned-tables.patch
>>
>> Automatically updatable views failed to handle partitioned tables.
>> Once that's fixed, WITH CHECK OPTIONS wouldn't work correctly without
>> the WCO expressions having been suitably converted for each partition
>> (think applying map_partition_varattnos to Vars in the WCO expressions
>> just like with partition constraint expressions).
> 
> The changes to execMain.c contain a hunk which has essentially the
> same code twice.  That looks like a mistake.  Also, the patch doesn't
> compile because convert_tuples_by_name() takes 3 arguments, not 4.

Actually, I realized that and sent the updated version [1] of this patch
that fixed this issue.  In the updated version, I removed that code block
(the 2 copies of it), because we are still discussing what to do about
showing tuples in constraint violation (in this case, WITH CHECK OPTION
violation) messages.  Anyway, attached here again.

>> 0006-Avoid-tuple-coversion-in-common-partitioning-cases.patch
>>
>> Currently, the tuple conversion is performed after a tuple is routed,
>> even if the attributes of a target leaf partition map one-to-one with
>> those of the root table, which is wasteful.  Avoid that by making
>> convert_tuples_by_name() return a NULL map for such cases.
> 
> +        Assert(!consider_typeid && indesc->tdhasoid == outdesc->tdhasoid);
> 
> I think you mean Assert(consider_typeid || indesc->tdhasoid ==
> outdesc->tdhasoid);

Ah, you're right.

> But I wonder why we don't instead just change this function to
> consider tdhasoid rather than tdtypeid.  I mean, if the only point of
> comparing the type OIDs is to find out whether the table-has-OIDs
> setting matches, we could instead test that directly and avoid needing
> to pass an extra argument.  I wonder if there's some other reason this
> code is there which is not documented in the comment...

With the following patch, regression tests run fine:

  if (indesc->natts == outdesc->natts &&
-     indesc->tdtypeid == outdesc->tdtypeid)
+     indesc->tdhasoid != outdesc->tdhasoid)
     {

If checking tdtypeid (instead of tdhasoid directly) has some other
consideration, I'd would have seen at least some tests broken by this
change.  So, if we are to go with this, I too prefer it over my previous
proposal to add an argument to convert_tuples_by_name().  Attached 0003
implements the above approach.

> Phew.  Thanks for all the patches, sorry I'm having trouble keeping up.

Thanks a lot for taking time to look through them and committing.

Thanks,
Amit

[1]
https://www.postgresql.org/message-id/92fe2a71-5eb7-ee8d-53ef-cfd5a65dfc3d%40lab.ntt.co.jp

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