On Sat, Oct 12, 2019 at 10:43 AM Justin Pryzby <pry...@telsasoft.com> wrote:
> On Sat, Oct 12, 2019 at 04:39:56PM +0200, Ivan Voras wrote: > > With seqscan disabled, I get this plan on 9.6: > > Bitmap Heap Scan on friend (cost=8.42..19.01 rows=14 width=8) > ... > > I expected to get an index-only scan in this situation, as that would be > a > > very common query. Is there a way to actually make this sort of query > > resolvable with an index-only scan? Maybe a different table structure > would > > help? > It would have to scan the entire index to find the cases where user2_id=42 but user1_id is not constrained. Technically User1_id would be constrained to be less than 42, but I don't think the planner will take that into account. > The v11 release notes have this relevant item: > > https://www.postgresql.org/docs/11/release-11.html > |Allow bitmap scans to perform index-only scans when possible (Alexander > Kuzmenkov) > > But this is not one of those cases. It is only possible when the only data needed is whether the row exists or not. Cheers, Jeff
