Hi, On 2022-09-30 12:13:11 -0400, Tom Lane wrote: > "kuroda.hay...@fujitsu.com" <kuroda.hay...@fujitsu.com> writes: > > Hmm, I was not sure about additional conditions, sorry. > > I could reproduce with followings steps: > > I tried this on a 32-bit VM with gcc 11.3, but couldn't reproduce. > You said earlier > > >> OS: RHEL 6.10 server > >> Arch: i686 > >> Gcc: 4.4.7 > > That is an awfully old compiler; I fear I no longer have anything > comparable on a working platform. > > The most likely theory, I think, is that that compiler is generating > slightly different floating-point code causing different plans to > be costed slightly differently than what the test case is expecting. > Probably, the different orderings of the keys in this test case have > exactly the same cost, or almost exactly, so that different roundoff > error could be enough to change the selected plan.
Yea. I suspect that's because that compiler version doesn't have -fexcess-precision=standard: > CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith > -Wdeclaration-after-statement -Werror=vla -Wendif-labels > -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -g > -O2 It's possible one could work around the issue with -msse -mfpmath=sse instead of -fexcess-precision=standard. Greetings, Andres Freund
