Anastasia Lubennikova <lubennikov...@gmail.com> writes:
> There is a question of support multicolumn index only scans for GIST.
> gistcanreturn() can return true if fetch is implemented for all indexed
> columns and false otherwise.
> But that's not very good case for multicolumn indexes.
> I think, it requires extend the interface to add separate columns checking.
> But I can't understand what kind of changes is required
> and how would it affect on previous amcanreturn interface.
Yeah, rather than just returning a bool, I suppose we need it to return
an indication of which index columns it's prepared to return values for.
(And then I guess the runtime API should return nulls for index columns
it can't handle.) You could probably use either a bitmapset or an integer
List to return the column numbers.
I wouldn't be too worried about backwards compatibility in changing that
API. If there are any people supporting outside-core index AMs, they've
got much bigger problems than this.
regards, tom lane
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