On Wed, Sep 3, 2014 at 2:13 PM, Peter Geoghegan <pg@heroku.com> wrote:
> On Wed, Sep 3, 2014 at 9:51 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>>> Essentially, the implementation has all stages of query processing
>>> During the execution of the parent ModifyTable, a special auxiliary
>>> subquery (the UPDATE ModifyTable) is considered as a special case.
>>> This is not a subplan of the ModifyTable node in the conventional
>>> sense, and so does not appear within EXPLAIN output.
>>
>> ...that sounds wonky.
>
> Which part? It certainly wouldn't be helpful if the (say) auxiliary
> plan's "sequential scan" appeared within EXPLAIN output. That's just
> an implementation detail. Note that the structure of the plan is
> highly restricted, since it needs to be "driven by the insert" (or,
> rather, the insert's conflicts, including conflicts not visible to the
> command's MVCC snapshot). There won't be any interesting variation in
> the plan. Although, that said, the implementation should probably
> display any "Filter: ..." conditions implied by the special UPDATE
> qual.
I think there shouldn't be any plan nodes in the system that don't get
displayed by explain. If you're using a plan node for something, and
think it shouldn't be displayed by explain, then either (1) you are
wrong or (2) you are abusing the plan node.
--
Robert Haas
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