fix: trampling on global physical size metric (#5663)

All loading (attached, or from disk) timelines overwrite the global
gauge for physical size. The `_set` method cannot be used safely, so
remove it and just "add" the physical size.

pageserver/src/metrics.rs

@@ -1388,27 +1388,22 @@ impl TimelineMetrics {
         }
     }
 
-    pub fn record_new_file_metrics(&self, sz: u64) {
+    pub(crate) fn record_new_file_metrics(&self, sz: u64) {
         self.resident_physical_size_add(sz);
         self.num_persistent_files_created.inc_by(1);
         self.persistent_bytes_written.inc_by(sz);
     }
 
-    pub fn resident_physical_size_sub(&self, sz: u64) {
+    pub(crate) fn resident_physical_size_sub(&self, sz: u64) {
         self.resident_physical_size_gauge.sub(sz);
         crate::metrics::RESIDENT_PHYSICAL_SIZE_GLOBAL.sub(sz);
     }
 
-    pub fn resident_physical_size_add(&self, sz: u64) {
+    pub(crate) fn resident_physical_size_add(&self, sz: u64) {
         self.resident_physical_size_gauge.add(sz);
         crate::metrics::RESIDENT_PHYSICAL_SIZE_GLOBAL.add(sz);
     }
 
-    pub fn resident_physical_size_set(&self, sz: u64) {
-        self.resident_physical_size_gauge.set(sz);
-        crate::metrics::RESIDENT_PHYSICAL_SIZE_GLOBAL.set(sz);
-    }
-
     pub fn resident_physical_size_get(&self) -> u64 {
         self.resident_physical_size_gauge.get()
     }

pageserver/src/tenant/timeline.rs

@@ -1871,7 +1871,7 @@ impl Timeline {
             "loaded layer map with {} layers at {}, total physical size: {}",
             num_layers, disk_consistent_lsn, total_physical_size
         );
-        self.metrics.resident_physical_size_set(total_physical_size);
+        self.metrics.resident_physical_size_add(total_physical_size);
 
         timer.stop_and_record();
         Ok(())