Re: CTE inlining

On Mon, May 1, 2017 at 7:26 AM, Andreas Karlsson <andreas(at)proxel(dot)se> wrote:

> On 05/01/2017 04:17 PM, David Fetter wrote:
>
>> Maybe we could allow a "decorator" that would tell the planner the CTE
>>> could be inlined?
>>>
>>> WITH INLINE mycte AS ( ...)
>>>
>>
>> +1 for a decorator, -1 for this one.
>>
>
> I am not sure I like decorators since this means adding an ad hoc query
> hint directly into the SQL syntax which is something which I requires
> serious consideration.

​Given that we already have
​"​
prevent optimization
​"​
syntax why do we need a decorator on the CTE?

>
>
> We already have an explicit optimization fence with OFFSET 0, and I
>> think making optimization fences explicit is how we should continue.
>> I'd be more in favor of something along the lines of
>>
>> WITH FENCED /* Somewhat fuzzy. What fence? */
>> or
>> WITH AT_MOST_ONCE /* Clearer, but not super precise */
>> or
>> WITH UNIQUE_ATOMIC /* More descriptive, but not super clear without
>> the docs in hand */
>>
>> or something along that line.
>>
>
> What about WITH MATERIALIZED, borrowing from the MySQL terminology
> "materialized subquery"?

​I would shorten that to "WITH MAT" except that I don't think that having
two way to introduce an optimization fence is worthwhile.

If we don't optimize SRFs-in-target-list, and thus avoid multiple function
evaluation for (composite_col).*, I believe a significant number of
intentional optimization fence uses will be safe but behavioral changes.

David J.