On Sat, Dec 7, 2024 at 4:03 AM Etsuro Fujita <etsuro.fuj...@gmail.com> wrote: > On Fri, Dec 6, 2024 at 2:37 AM Robert Haas <robertmh...@gmail.com> wrote: > > I have a hard time seeing how this would work if cursors are in use on > > the main server. Say I do this: > > > > DECLARE foo CURSOR FOR SELECT * FROM ft1 UNION ALL SELECT * FROM ft2; > > ...fetch some rows from cursor foo but few enough that we only scan ft1... > > ...do something that causes a snapshot refresh like issue another query... > > ...fetch more rows from cursor foo until we start scanning ft2... > > Good point! Maybe my explanation was not enough, but the proposed > patch does not allow any query to do a snapshot refresh if such open > cursors exist on the main server, so cursor foo is guaranteed to scan > ft2 using the same snapshot that was used to scan ft1.
OK, I see. That does prevent the hazard I mentioned, but it also means that the results returned by a query are dependent on whether there's an unrelated cursor open, which seems unfortunate. -- Robert Haas EDB: http://www.enterprisedb.com
