On Thu, Feb 4, 2021 at 11:45 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > Amit Langote <amitlangot...@gmail.com> writes: > > On Thu, Feb 4, 2021 at 4:24 PM Kohei KaiGai <kai...@heterodb.com> wrote: > >> I think that MaxHeapAttributeNumber is a senseless restriction for foreign- > >> tables. How about your opinions? > > > My first reaction to this was a suspicion that the > > MaxHeapAttributeNumber limit would be too ingrained in PostgreSQL's > > architecture to consider this matter lightly, but actually browsing > > the code, that may not really be the case. > > You neglected to search for MaxTupleAttributeNumber...
Ah, I did. Although, even its usage seems mostly limited to modules under src/backend/access/heap. > I'm quite skeptical of trying to raise this limit significantly. > > In the first place, you'd have to worry about the 2^15 limit on > int16 AttrNumbers --- and keep in mind that that has to be enough > for reasonable-size joins, not only an individual table. If you > join a dozen or so max-width tables, you're already most of the way > to that limit. > > In the second place, as noted by the comment you quoted, there are > algorithms in various places that are O(N^2) (or maybe even worse?) > in the number of columns they're dealing with. Those are certainly intimidating considerations. -- Amit Langote EDB: http://www.enterprisedb.com
