ccache: disable

hosts/modules/roles/build-machine.nix

@@ -50,16 +50,19 @@ in
 
       nix.settings.system-features = [ "big-parallel" ];
 
-      programs.ccache.enable = true;
-      nix.settings.extra-sandbox-paths = [ "/var/cache/ccache" ];
-      sane.persist.sys.byStore.plaintext = [
-        { group = "nixbld"; mode = "0775"; path = "/var/cache/ccache"; method = "bind"; }
-      ];
-      # `sloppiness = random_seed`: see <https://wiki.nixos.org/wiki/CCache#Sloppiness>
-      sane.fs."/var/cache/ccache/ccache.conf".file.text = ''
-        max_size = 50G
-        sloppiness = random_seed
-      '';
+      # XXX(2024-xx): ccache _works_, but the cache hit rate is so low that it's often a net negative!
+      # ElvishJerricco linked his ccache config in #nix-offtopic 2024-11-09, claiming he got it to
+      # actually speed things up with the right env vars; didn't see anything obvious there.
+      # programs.ccache.enable = true;
+      # nix.settings.extra-sandbox-paths = [ "/var/cache/ccache" ];
+      # sane.persist.sys.byStore.plaintext = [
+      #   { group = "nixbld"; mode = "0775"; path = "/var/cache/ccache"; method = "bind"; }
+      # ];
+      # # `sloppiness = random_seed`: see <https://wiki.nixos.org/wiki/CCache#Sloppiness>
+      # sane.fs."/var/cache/ccache/ccache.conf".file.text = ''
+      #   max_size = 50G
+      #   sloppiness = random_seed
+      # '';
 
       # corresponds to env var: NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1
       # nixpkgs.config.allowUnsupportedSystem = true;

overlays/pkgs-ccache.nix

@@ -1,5 +1,5 @@
 # `pkgsCCcache.foo`: builds `foo`, using the `ccache` compiler so that incremental builds are cheaper.
-# requires `programs.ccache.enable = true`.
+# requires `programs.ccache.enable = true`  (see: </hosts/modules/roles/build-machine.nix>)
 #
 # common operations:
 # - `nix-ccache --show-stats`