Re: UPDATE of partition key

On Thu, May 11, 2017 at 5:45 PM, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> wrote:
> On 11 May 2017 at 17:24, Amit Kapila <amit(dot)kapila16(at)gmail(dot)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? Is it because we can't find root partition
from leaf partition?

+ is_partitioned_table =
+ root_rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE;
+
+ if (is_partitioned_table)
+ ExecSetupPartitionTupleRouting(
+ root_rel,
+ /* Build WITH CHECK OPTION constraints for leaf partitions */
+ ExecInitPartitionWithCheckOptions(mtstate, root_rel);
+ /* Build a projection for each leaf partition rel. */
+ ExecInitPartitionReturningProjection(mtstate, root_rel);
..
+ /* It's not a partitioned table after all; error out. */
+ ExecPartitionCheckEmitError(resultRelInfo, slot, estate);

When we are anyway going to give error if table is not a partitioned
table, then isn't it better to give it early when we first identify
that.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com