boron: move postgresqlBackup to disk to reduce ram pressure

hosts/boron.cx.ts.hillion.co.uk/default.nix

@@ -41,7 +41,14 @@
     fileSystems."/nix".options = [ "compress=zstd" ];
 
     ## Impermanence
-    custom.impermanence.enable = true;
+    custom.impermanence = {
+      enable = true;
+      cache.enable = true;
+    };
+    boot.initrd.postDeviceCommands = lib.mkAfter ''
+      btrfs subvolume delete /cache/system
+      btrfs subvolume snapshot /cache/empty_snapshot /cache/system
+    '';
 
     ## Custom Services
     custom = {

hosts/boron.cx.ts.hillion.co.uk/hardware-configuration.nix

@@ -35,6 +35,13 @@
       options = [ "subvol=data" ];
     };
 
+  fileSystems."/cache" =
+    {
+      device = "/dev/disk/by-uuid/9aebe351-156a-4aa0-9a97-f09b01ac23ad";
+      fsType = "btrfs";
+      options = [ "subvol=cache" ];
+    };
+
   fileSystems."/nix" =
     {
       device = "/dev/disk/by-uuid/9aebe351-156a-4aa0-9a97-f09b01ac23ad";

hosts/sodium.pop.ts.hillion.co.uk/default.nix

@@ -22,12 +22,14 @@
     fileSystems."/nix".options = [ "compress=zstd" ];
 
     ## Impermanence
-    custom.impermanence.enable = true;
+    custom.impermanence = {
+      enable = true;
+      cache.enable = true;
+    };
     boot.initrd.postDeviceCommands = lib.mkAfter ''
       btrfs subvolume delete /cache/tmp
       btrfs subvolume snapshot /cache/empty_snapshot /cache/tmp
-      chmod 0777 /cache/tmp
-      chmod +t /cache/tmp
+      chmod 1777 /cache/tmp
     '';
 
     ## CA server

modules/impermanence.nix

@@ -11,6 +11,13 @@ in
       type = lib.types.str;
       default = "/data";
     };
+    cache = {
+      enable = lib.mkEnableOption "impermanence.cache";
+      path = lib.mkOption {
+        type = lib.types.str;
+        default = "/cache";
+      };
+    };
 
     users = lib.mkOption {
       type = with lib.types; listOf str;
@@ -39,7 +46,9 @@ in
       gitea.stateDir = "${cfg.base}/system/var/lib/gitea";
     };
 
-    environment.persistence."${cfg.base}/system" = {
+    environment.persistence = lib.mkMerge [
+      {
+        "${cfg.base}/system" = {
           hideMounts = true;
 
           directories = [
@@ -53,6 +62,15 @@ in
           (lib.lists.optional config.services.tang.enable "/var/lib/private/tang") ++
           (lib.lists.optional config.services.step-ca.enable "/var/lib/step-ca/db");
         };
+      }
+      (lib.mkIf cfg.cache.enable {
+        "${cfg.cache.path}/system" = {
+          hideMounts = true;
+
+          directories = (lib.lists.optional config.services.postgresqlBackup.enable config.services.postgresqlBackup.location);
+        };
+      })
+    ];
 
     home-manager.users =
       let