What’s the fastest compiler for PostgreSQL? Let’s take a look.

OS Compiler time make -s
macOS 13 gcc-13 3:59.29
  gcc-12 3:42.19
  gcc-11 3:33.35
  clang-16 3:05.05
  clang-15 2:19.71
  clang-14 2:21.03
  clang-13 2:20.72
  Apple clang (14) 1:55.87
Ubuntu 22.04 gcc-12 (default) 2:57.87
  gcc-11 2:24.20
  gcc-10 2:18.28
  clang-15 2:21.62
  clang-14 2:24.23
  clang-13 2:25.68

Compilers keep getting slower, it appears! Maybe don’t use the latest one right away!

Also, gcc vs clang? Not sure, it depends.

The above uses the default optimization level -O2. Let’s see if we can squeeze out more:

Optimization Apple clang gcc-13
-O3 1:55.10 4:26.59
-O2 1:52.13 4:08.09
-Og 1:49.22 2:46.33
-O1 1:48.15 3:07.30
-Os 1:49.47 3:36.30
-Oz 1:44.37 3:36.18
-O0 1:07.65 2:29.51

So on the clang side, to get any real benefit, you need to go all the way to -O0, which I don’t recommend for general use, because then you don’t get many of the helpful compiler warnings. On the gcc side, it might be beneficial to use one of the intermediate levels to get better performance.

Let’s also test how well parallelism works:

Parallelism Apple clang gcc-13
-j1 1:55.87 4:09.10
-j2 1:02.33 2:11.77
-j3 46.261 1:36.65
-j4 38.298 1:19.08
-j5 34.003 1:07.55
-j6 30.118 1:00.89
-j7 27.844 56.712
-j8 25.857 51.929
-j9 25.502 50.734
-j10 25.046 49.071
-j11 24.778 50.758
-j12 24.358 48.825
-j13 24.571 48.655
-j (unlimited) 26.891 1:00.23

The arithmetic here is unsurprising up to a point. This machine has 12 CPU cores, so you get speedups until around -j12. But it’s notable that the gains level off at 8. It could be because there are 8 “performance” cores and 4 “efficiency” cores, and the efficiency cores aren’t that helpful for this? Or maybe because there is just not that much more parallelism to be had in the build.

So, to conclude, there is a large range in the time measurements here. You can go from more than 4 minutes for a build to about 25 seconds with the right choice of compiler and build options. Obviously, the absolute numbers will vary for everyone depending on the hardware and available software. But it’s worth exploring!

Of course, there are several other components that affect build and test cycle performance, including ccache, configure vs. meson, make vs. ninja, choice of linker, PostgreSQL build options, and so on. More articles to come.

Details on the methodology:

  • All tests in this article were done on tag REL_16_BETA1.

  • Ccache was disabled by export CCACHE_DISABLE=1.

  • Timings were done like this: git clean -fdx; ./configure CC=xxx; time make -s