From 1f1cd9b5ddc6e7464c1c7416bcce7007fe3bc88c Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 3 May 2018 18:06:45 -0400 Subject: [PATCH] Avoid overwriting unchanged output files in genbki.pl and Gen_fmgrtab.pl. If a particular output file already exists with the contents it should have, leave it alone, so that its mod timestamp is not advanced. In builds using --enable-depend, this can avoid the need to recompile .c files whose included files didn't actually change. It's not clear whether it saves much of anything for users of ccache; but the cost of doing the file comparisons seems to be negligible, so we might as well do it. For developers using the MSVC toolchain, this will create a regression: msvc/Solution.pm will sometimes run genbki.pl or Gen_fmgrtab.pl unnecessarily. I'll look into fixing that separately. Discussion: https://postgr.es/m/16925.1525376229@sss.pgh.pa.us --- src/backend/catalog/Catalog.pm | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/src/backend/catalog/Catalog.pm b/src/backend/catalog/Catalog.pm index eee7cb3b90..2889cb9fb0 100644 --- a/src/backend/catalog/Catalog.pm +++ b/src/backend/catalog/Catalog.pm @@ -16,6 +16,9 @@ package Catalog; use strict; use warnings; +use File::Compare; + + # Parses a catalog header file into a data structure describing the schema # of the catalog. sub ParseHeader @@ -336,15 +339,29 @@ sub AddDefaultValues } # Rename temporary files to final names. -# Call this function with the final file name and the .tmp extension +# Call this function with the final file name and the .tmp extension. +# +# If the final file already exists and has identical contents, don't +# overwrite it; this behavior avoids unnecessary recompiles due to +# updating the mod date on unchanged header files. +# # Note: recommended extension is ".tmp$$", so that parallel make steps -# can't use the same temp files +# can't use the same temp files. sub RenameTempFile { my $final_name = shift; my $extension = shift; my $temp_name = $final_name . $extension; - rename($temp_name, $final_name) || die "rename: $temp_name: $!"; + + if (-f $final_name + && compare($temp_name, $final_name) == 0) + { + unlink $temp_name || die "unlink: $temp_name: $!"; + } + else + { + rename($temp_name, $final_name) || die "rename: $temp_name: $!"; + } } # Find a symbol defined in a particular header file and extract the value. -- 2.40.0