On Wed, Mar 7, 2018 at 8:55 AM, Stephen Frost <sfr...@snowman.net> wrote: > Greetings Robert, Ashutosh, Arthur, Etsuro, all, > > * Arthur Zakirov (a.zaki...@postgrespro.ru) wrote: >> On Tue, Mar 06, 2018 at 08:09:50PM +0900, Etsuro Fujita wrote: >> > Agreed. I added a comment to that function. I think that that comment in >> > combination with changes to the FDW docs in the patch would help FDW >> > authors >> > understand why that is needed. Please find attached an updated version of >> > the patch. >> >> Thank you. >> >> All tests pass, the documentation builds. There was the suggestion [1] >> of different approach. But the patch fix the issue in much more simple >> way. >> >> Marked as "Ready for Commiter". >> >> 1 - >> https://www.postgresql.org/message-id/20171005.200631.134118679.horiguchi.kyotaro%40lab.ntt.co.jp > > Thanks, I've looked through this patch and thread again and continue to > feel that this is both a good and sensible improvment and that the patch > is in pretty good shape. > > The remaining question is if the subsequent discussion has swayed the > opinion of Robert and Ashutosh. If we can get agreement that these > semantics are acceptable and an improvement over the status quo then I'm > happy to try and drive this patch to commit. > > Robert, Ashutosh?
If there is a local constraint on the foreign table, we don't check it. So, a row that was inserted through this foreign table may not show up when selected from the foreign table. Apply same logic to the WCO on a view on the foreign table, it should be fine if a row inserted through the view doesn't show up in the view. Somebody who created the view, knew that it's a foreign table underneath. Stephen said [1] that the view is local and irrespective of what's underneath it, it should obey WCO. Which seems to be a fair point when considered alone, but with the above context, it doesn't look any fair. Etsuro said [2] that WCO constraints can not be implemented on foreign server and normal check constraints can be, and for that he provides an example in [3]. But I think that example is going the wrong direction. For local constraints to be enforced, we use remote constraints. For local WCO we need to use remote WCO. That means we create many foreign tables pointing to same local table on the foreign server through many views, but it's not impossible. [1] https://www.postgresql.org/message-id/20180117130021.GC2416%40tamriel.snowman.net [2] https://www.postgresql.org/message-id/5A058F21.2040201%40lab.ntt.co.jp [3] https://www.postgresql.org/message-id/a3955a1d-ad07-5b0a-7618-b6ef5ff0e1c5%40lab.ntt.co.jp -- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
