Re: Should we add GUCs to allow partition pruning to be disabled?

Amit Langote wrote:

> Sorry, I should have said what I said after quoting only the last sentence
> of what you had said.  That is, I want to the new GUC to be the only
> determiner of whether the pruning occurs or not for partitioned tables.
> To implement that behavior, it will have to override the setting of
> constraint_exclusion (the parameter) in *some* cases, because some
> commands still rely on constraint exclusion (the algorithm) as the
> underlying pruning mechanism.

I agree -- it will make more sense now, and will continue to make sense
later when we remove usage of constraint exclusion for upd/del, to make
it work as you suggest:

* if the table is partitioned, do constraint exclusion based on
  enable_partition_prune=on rather than constraint_exclusion=partition.
  This will only affect upd/del, because the select queries would be
  affected by the enable_partition_prune anyway since
  constraint_exclusion does not apply.

* If the table is using regular inheritance, continue to use the
  original behavior.

> Now, the "override the setting of constraint_exclusion" implementation
> may not be the most popular choice in the end.

I guess there are different ways to implement it.  Supposedly this is
going to disappear in pg12, so I don't think it's a big deal.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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