On Tue, 22 Apr 2025 at 18:40, Pavel Borisov <pashkin.e...@gmail.com> wrote: > > Hi, Tom! > > On Tue, 22 Apr 2025 at 18:23, Tom Lane <t...@sss.pgh.pa.us> wrote: > > > > Pavel Borisov <pashkin.e...@gmail.com> writes: > > > It's not a big problem, but propose a simple fix for the tests. It > > > just adds ORDER BY 1 to all relevant float4 and floa8 queries. > > > > You do realize that this problem is hardly confined to the > > float4 and float8 tests? To a first approximation, a table AM > > that fails to preserve insertion order would break every single > > one of our regression tests. (I speak from experience, as > > Salesforce had to deal with this when I was there...) > > > > The reason why we don't simply add ORDER BY to everything is > > explained at [1]: > > > > You might wonder why we don't order all the regression test > > queries explicitly to get rid of this issue once and for all. The > > reason is that that would make the regression tests less useful, > > not more, since they'd tend to exercise query plan types that > > produce ordered results to the exclusion of those that don't. > > > > At some point we will probably have to think through what we > > want to do about running the regression tests with table AMs that > > don't wish to preserve ordering as much as heapam does. It's going > > to need careful balancing of multiple concerns, and I don't think > > "blindly slap ORDER BY everywhere" is going to be an acceptable > > answer. > > > > I agree we might need to elaborate different AM support in regression tests. > Also, I agree that these are not the only tests to be fixed. > > What I hardly agree with, is that we suppose it's right for regression > tests to require some fixed results ordering for so simple cases. > Maybe for more complicated plans it's useful, but for the float tests > mentioned in the patch it's this requirement is a total loss IMO. > > I understand your sentiment against blindly slapping order by's, but I > don't see a useful alternative for this time. Also a large number of > tests in PG were already fortified with ORDER BY 1.
I forgot to mention that it's not only a question of INSERTs ordering. Extension AM can have some internal ordering e.g. index-organized tables. And besides SELECT query results following internal AM ordering just being allowed, more importantly they are good performance-wise and justify table AM extensibility. Regards, Pavel.
