Tomas Vondra <tomas.von...@enterprisedb.com> writes: > The one difference is that I realized the relkind check does not > actually say we can't do sampling - it just means we can't use > TABLESAMPLE to do it. We could still use "random()" ...
> Furthermore, I don't think we should silently disable sampling when the > user explicitly requests TABLESAMPLE by specifying bernoulli/system for > the table - IMHO it's less surprising to just fail in that case. Agreed on both points. This patch looks good to me. > Of course, all relkinds that don't support TABLESAMPLE currently have > reltuples value that will disable sampling anyway (e.g. views have -1). > So we won't actually fallback to random() anyway, because we can't > calculate the sample fraction. > That's a bit annoying for foreign tables pointing at a view, which is a > more likely use case than table pointing at a sequence. Right, that's a case worth being concerned about. > But I realized we could actually still do "random()" sampling: > SELECT * FROM t ORDER BY random() LIMIT $X; Hmm, interesting idea, but it would totally bollix our correlation estimates. Not sure that those are worth anything for remote views, but still... regards, tom lane