Re: xid wraparound danger due to INDEX_CLEANUP false

On Fri, Nov 20, 2020 at 4:21 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Actually, now I think that BRIN shouldn't be special to vacuumlazy.c
> in any way. It doesn't make sense as part of this future world in
> which index vacuuming can be skipped for individual indexes (which is
> what I talked to Sawada-san about a little earlier in this thread).
> Why should it be useful to exploit the "no-real-TIDs" property of BRIN
> in this future world? It can only solve a problem that the main
> enhancement is itself expected to solve without any special help from
> BRIN (just the generic am callback that asks the same generic question
> about index vacuuming urgency).
>
> The only reason we press ahead with a second scan (the
> LP_DEAD-to-LP_UNUSED thing) in this ideal world is a heap/table
> problem. The bloat eventually gets out of hand *in the table*. We have
> now conceptually decoupled the problems experienced in the table/heap
> from the problems for each index (mostly), so this actually makes
> sense. The theory behind AV scheduling becomes much closer to reality
> -- by changing the reality! (The need to "prune the table to VACUUM
> any one index" notwithstanding -- that's still necessary, of course,
> but we still basically decouple table bloat from index bloat at the
> conceptual level.)
>
> Does that make sense?

I *think* so. For me the point is that the index never has a right to
insist on being vacuumed, but it can offer an opinion on how helpful
it would be.

--
Robert Haas
EDB: http://www.enterprisedb.com