Use saturating_sub for resident_physical_size_gauge

to avoid metric overflow, if the gauge is not initialized yet.

Cargo.lock

@@ -3067,15 +3067,6 @@ dependencies = [
  "workspace_hack",
 ]
 
-[[package]]
-name = "remove_dir_all"
-version = "0.5.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3acd125665422973a33ac9d3dd2df85edad0f4ae9b00dafb1a05e43a9f5ef8e7"
-dependencies = [
- "winapi",
-]
-
 [[package]]
 name = "reqwest"
 version = "0.11.14"
@@ -3849,16 +3840,15 @@ dependencies = [
 
 [[package]]
 name = "tempfile"
-version = "3.3.0"
+version = "3.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5cdb1ef4eaeeaddc8fbd371e5017057064af0911902ef36b39801f67cc6d79e4"
+checksum = "af18f7ae1acd354b992402e9ec5864359d693cd8a79dcbef59f76891701c1e95"
 dependencies = [
  "cfg-if",
  "fastrand",
- "libc",
  "redox_syscall",
- "remove_dir_all",
- "winapi",
+ "rustix",
+ "windows-sys 0.42.0",
 ]
 
 [[package]]

Cargo.toml

@@ -150,7 +150,7 @@ workspace_hack = { version = "0.1", path = "./workspace_hack/" }
 criterion = "0.4"
 rcgen = "0.10"
 rstest = "0.16"
-tempfile = "3.2"
+tempfile = "3.4"
 tonic-build = "0.8"
 
 # This is only needed for proxy's tests.

pageserver/src/tenant/timeline.rs

@@ -1082,7 +1082,10 @@ impl Timeline {
                 }
 
                 if let Some(layer_size) = layer_size {
-                    self.metrics.resident_physical_size_gauge.sub(layer_size);
+                    let current_size = self.metrics.resident_physical_size_gauge.get();
+                    self.metrics
+                        .resident_physical_size_gauge
+                        .set(current_size.saturating_sub(layer_size));
                 }
 
                 true
@@ -1504,7 +1507,11 @@ impl Timeline {
                             assert!(local_layer_path.exists(), "we would leave the local_layer without a file if this does not hold: {}", local_layer_path.display());
                             anyhow::bail!("could not rename file {local_layer_path:?}: {err:?}");
                         } else {
-                            self.metrics.resident_physical_size_gauge.sub(local_size);
+                            let current_size = self.metrics.resident_physical_size_gauge.get();
+                            self.metrics
+                                .resident_physical_size_gauge
+                                .set(current_size.saturating_sub(local_size));
+
                             updates.remove_historic(local_layer);
                             // fall-through to adding the remote layer
                         }
@@ -1946,7 +1953,10 @@ impl Timeline {
 
         layer.delete()?;
         if let Some(layer_size) = layer_size {
-            self.metrics.resident_physical_size_gauge.sub(layer_size);
+            let current_size = self.metrics.resident_physical_size_gauge.get();
+            self.metrics
+                .resident_physical_size_gauge
+                .set(current_size.saturating_sub(layer_size));
         }
 
         // TODO Removing from the bottom of the layer map is expensive.