Re: [HACKERS] [Proposal] Allow users to specify multiple tables inVACUUM commands

On Sat, Aug 26, 2017 at 8:00 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Aug 24, 2017 at 12:59 AM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
>> Robert, Amit and other folks working on extending the existing
>> partitioning facility would be in better position to answer that, but
>> I would think that we should have something as flexible as possible,
>> and storing a list of relation OID in each VacuumRelation makes it
>> harder to track the uniqueness of relations vacuumed. I agree that the
>> concept of a partition with multiple parents induces a lot of
>> problems. But the patch as proposed worries me as it complicates
>> vacuum() with a double loop: one for each relation vacuumed, and one
>> inside it with the list of OIDs. Modules calling vacuum() could also
>> use flexibility, being able to analyze a custom list of columns for
>> each relation has value as well.
>
> So ... why have a double loop?  I mean, you could just expand this out
> to one entry per relation actually being vacuumed, couldn't you?

Yes, if I understand that correctly. That's the point I am exactly
coming at. My suggestion is to have one VacuumRelation entry per
relation vacuumed, even for partitioned tables, and copy the list of
columns to each one.

> +    oldcontext = MemoryContextSwitchTo(vac_context);
> +    foreach(lc, relations)
> +        temp_relations = lappend(temp_relations, copyObject(lfirst(lc)));
> +    MemoryContextSwitchTo(oldcontext);
> +    relations = temp_relations;
>
> Can't we just copyObject() on the whole list?

Yup.
-- 
Michael