On Fri, Oct 28, 2022 at 10:28 AM David Rowley <dgrowle...@gmail.com> wrote: > > On Fri, 28 Oct 2022 at 16:51, Amul Sul <sula...@gmail.com> wrote: > > > > On Thu, Oct 27, 2022 at 6:54 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > > > Please be specific about the circumstances in which the output is > > > unstable for you. With zero information to go on, it seems about as > > > likely that this change is masking a bug as that it's a good idea. > > > > > > > At the first glance, I thought the patch is pretty much obvious, and > > we usually add an ORDER BY clause to ensure stable output. > > Unfortunately, you'll need to do better than that. We're not in the > business of accepting patches with zero justification for why they're > required. If you're not willing to do the analysis on why the order > changes sometimes, why should we accept your patch? >
Unfortunately the test is not failing at me. Otherwise, I would have done that analysis. When I saw the patch for the first time, somehow, I didn't think anything spurious due to my misconception that we usually add the ORDER BY clause for the select queries just to be sure. > If you can't find the problem then you should modify insert.sql to > EXPLAIN the problem query to see if the plan has changed between the > passing and failing run. The only thing that comes to mind about why > this test might produce rows in a different order would be if a > parallel Append was sorting the subpaths by cost (See > create_append_path's call to list_sort) and the costs were for some > reason coming out differently sometimes. It's hard to imagine why this > query would be parallelised though. If you show us the EXPLAIN from a > passing and failing run, it might help us see the problem. > Understood. > > If we > > are too sure that the output usually comes in the same order then the > > ORDER BY clause that exists in other tests seems useless. I am a bit > > confused & what could be a possible bug? > > You can't claim that if this test shouldn't get an ORDER BY that all > tests shouldn't have an ORDER BY. That's just crazy. What if the test > is doing something like testing sort?! > That I can understand that the sorted output doesn't need further sorting. I am just referring to the simple SELECT queries that do not have any sorting. Thanks & Regards, Amul
