Re: Indirect indexes

On Fri, Oct 21, 2016 at 7:04 PM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Robert Haas wrote:
>> So, I think that this is a really promising direction, but also that
>> you should try very hard to try to get out from under this 6-byte PK
>> limitation.  That seems really ugly, and in practice it probably means
>> your PK is probably going to be limited to int4, which is kind of sad
>> since it leaves people using int8 or text PKs out in the cold.
>
> I think we could just add a new type, unsigned 6 byte int, specifically
> for this purpose.  Little in the way of operators, as it's pointless to
> try to do arithmetic with object identifiers.  (It'd be similar to UUID
> in spirit, but I wouldn't try to do anything too smart to generate them.)

Sure, we could do that, but that's just band-aiding over the fact that
the index page format isn't really what we want for a feature of this
type.

> Yes, recheck is always needed.
>
> As for vacuum, I was thinking this morning that perhaps the answer to
> that is just to not vacuum the index at all and instead rely on the
> killtuple interface (which removes tuples during scan).  So we don't
> need to spend precious maint_work_mem space on a large list of PK
> values.

I don't think that's going to fly.  Even if it's the case that
indirect indexes typically need less cleanup than regular indexes, the
idea that there's no command to force a full cleanup short of REINDEX
doesn't sit well with me.  It's not difficult to construct realistic
scenarios in which kill_prior_tuple is almost useless (e.g. values are
all marching forward).

-- 
Robert Haas
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