Hi, Thanks for the detailed explanation!
On Mon, Aug 21, 2023 at 10:34 PM Önder Kalacı <onderkal...@gmail.com> wrote: >> As described in the commit message, we assume that extensions use the >> hook in a similar way to FDWs > I'm not sure if it is fair to assume that extensions use any hook in any way. I am not sure either, but as for the hook, I think it is an undeniable fact that the core system assumes that extensions will use it in that way. >> So my question is: does the Citus extension use the hook like this? >> (Sorry, I do not fully understand Onder's explanation.) > I haven't gone into detail about how Citus uses this hook, but I don't think > we should > need to explain it. In general, Citus uses many hooks, and many other > extensions > use this specific hook. With minor version upgrades, we haven't seen this > kind of > behavior change before. > > In general, Citus relies on this hook for collecting information about joins > across > relations/ctes/subqueries. So, its scope is bigger than a single join for > Citus. > > The extension assigns a special marker(s) for RTE Relations, and then checks > whether > all relations with these special markers joined transitively across > subqueries, such that > it can decide to pushdown the whole or some parts of the (sub)query. IIUC, I think that that is going beyond what the hook supports. > But the bigger issue is that there has usually been a clear line between the > extensions and > the PG itself when it comes to hooks within the minor version upgrades. > Sadly, this change > breaks that line. We wanted to share our worries here and find out what > others think. My understanding is: at least for hooks with intended usages, if an extension uses them as intended, it is guaranteed that the extension as-is will work correctly with minor version upgrades; otherwise it is not necessarily. I think it is unfortunate that my commit broke the Citus extension, though. >> >Except that this was only noticed after it was released in a set of minor >> > versions, I would say that 6f80a8d9c should just straight up be reverted. > I cannot be the one to ask for reverting a commit in PG, but I think doing it > would be a > fair action. We kindly ask those who handle this to think about it. Reverting the commit would resolve your issue, but re-introduce the issue mentioned upthread to extensions that use the hook properly, so I do not think that reverting the commit would be a fair action. Sorry for the delay. Best regards, Etsuro Fujita
