Horton

Re: UPDATE of partition key

Amit Khandekar <amitdkhan.pg@gmail.com>

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From: Amit Khandekar <amitdkhan.pg@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-05-12T05:23:49Z
Lists: pgsql-hackers 
On 12 May 2017 at 10:01, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Fri, May 12, 2017 at 9:27 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> On Thu, May 11, 2017 at 5:45 PM, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
>>> On 11 May 2017 at 17:24, Amit Kapila <amit.kapila16@gmail.com> wrote:
>>>> Few comments:
>>>> 1.
>>>> Operating directly on partition doesn't allow update to move row.
>>>> Refer below example:
>>>> create table t1(c1 int) partition by range(c1);
>>>> create table t1_part_1 partition of t1 for values from (1) to (100);
>>>> create table t1_part_2 partition of t1 for values from (100) to (200);
>>>> insert into t1 values(generate_series(1,11));
>>>> insert into t1 values(generate_series(110,120));
>>>>
>>>> postgres=# update t1_part_1 set c1=122 where c1=11;
>>>> ERROR:  new row for relation "t1_part_1" violates partition constraint
>>>> DETAIL:  Failing row contains (122).
>>>
>>> Yes, as Robert said, this is expected behaviour. We move the row only
>>> within the partition subtree that has the update table as its root. In
>>> this case, it's the leaf partition.
>>>
>>
>> Okay, but what is the technical reason behind it?  Is it because the
>> current design doesn't support it or is it because of something very
>> fundamental to partitions?
No, we can do that if decide to update some table outside the
partition subtree. The reason is more of semantics. I think the user
who is running UPDATE for a partitioned table, should not be
necessarily aware of the structure of the complete partition tree
outside of the current subtree. It is always safe to return error
instead of moving the data outside of the subtree silently.

>>
>
> One plausible theory is that as Select's on partitions just returns
> the rows of that partition, the update should also behave in same way.

Yes , right. Or even inserts fail if we try to insert data that does
not fit into the current subtree.


-- 
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company

Commits

  1. Avoid referencing off the end of subplan_partition_offsets.

  2. Allow UPDATE to move rows between partitions.

  3. Remove useless lookup of root partitioned rel in ExecInitModifyTable().

  4. Factor error generation out of ExecPartitionCheck.

  5. Minor preparatory refactoring for UPDATE row movement.

  6. Simplify and encapsulate tuple routing support code.

  7. Avoid coercing a whole-row variable that is already coerced.

  8. Use ResultRelInfo ** rather than ResultRelInfo * for tuple routing.

  9. Make RelationGetPartitionDispatchInfo expand depth-first.

  10. Expand partitioned tables in PartDesc order.

  11. Use a real RT index when setting up partition tuple routing.

  12. Fix transition tables for partition/inheritance.

  13. Fix confusion about number of subplans in partitioned INSERT setup.

  14. Prevent BEFORE triggers from violating partitioning constraints.

  15. Fire per-statement triggers on partitioned tables.

  16. Fix reporting of violations in ExecConstraints, again.

  17. Don't scan partitioned tables.

  18. Allow FDWs to push down quals without breaking EvalPlanQual rechecks.