Horton

Re: UPDATE of partition key

Amit Langote <langote_amit_f8@lab.ntt.co.jp>

View thread View on postgr.es
From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
To: Amit Khandekar <amitdkhan.pg@gmail.com>, David Fetter <david@fetter.org>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-02-16T07:27:39Z
Lists: pgsql-hackers 
On 2017/02/16 15:50, Amit Khandekar wrote:
> On 15 February 2017 at 20:26, David Fetter <david@fetter.org> wrote:
>> When an UPDATE can't happen, there are often ways to hint at
>> what went wrong and how to correct it.  Violating a uniqueness
>> constraint would be one example.
>>
>> When an UPDATE can't happen and the depth of the subtree is a
>> plausible candidate for what prevents it, there might be a way to say
>> so.
>>
>> Let's imagine a table called log with partitions on "stamp" log_YYYY
>> and subpartitions, also on "stamp", log_YYYYMM.  If you do something
>> like
>>
>>     UPDATE log_2017 SET "stamp"='2016-11-08 23:03:00' WHERE ...
>>
>> it's possible to know that it might have worked had the UPDATE taken
>> place on log rather than on log_2017.
>>
>> Does that make sense, and if so, is it super invasive to HINT that?
> 
> Yeah, I think it should be possible to find the root partition with

I assume you mean root *partitioned* table.

> the help of pg_partitioned_table,

The pg_partitioned_table catalog does not store parent-child
relationships, just information about the partition key of a table.  To
get the root partitioned table, you might want to create a recursive
version of get_partition_parent(), maybe called
get_partition_root_parent().  By the way, get_partition_parent() scans
pg_inherits to find the inheritance parent.

> and then run ExecFindPartition()
> again using the root. Will check. I am not sure right now how involved
> that would turn out to be, but I think that logic would not change the
> existing code, so in that sense it is not invasive.

I couldn't understand why run ExecFindPartition() again on the root
partitioned table, can you clarify?  ISTM, we just want to tell the user
in the HINT that trying the same update query with root partitioned table
might work.  I'm not sure if it would work instead to find some
intermediate partitioned table (that is, between the root and the one that
update query was tried with) to include in the HINT.

Thanks,
Amit

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.