add ability to have fake metrics (needed in next patch so we can have to Timeline objects with the same id in memory)

pageserver/src/metrics.rs

@@ -720,6 +720,7 @@ impl StorageTimeMetrics {
 
 #[derive(Debug)]
 pub struct TimelineMetrics {
+    fake: bool,
     tenant_id: String,
     timeline_id: String,
     pub reconstruct_time_histo: Histogram,
@@ -744,6 +745,7 @@ pub struct TimelineMetrics {
 
 impl TimelineMetrics {
     pub fn new(
+        fake: bool,
         tenant_id: &TenantId,
         timeline_id: &TimelineId,
         evictions_with_low_residence_duration_builder: EvictionsWithLowResidenceDurationBuilder,
@@ -797,7 +799,8 @@ impl TimelineMetrics {
         let evictions_with_low_residence_duration =
             evictions_with_low_residence_duration_builder.build(&tenant_id, &timeline_id);
 
-        TimelineMetrics {
+        let m = TimelineMetrics {
+            fake,
             tenant_id,
             timeline_id,
             reconstruct_time_histo,
@@ -819,12 +822,16 @@ impl TimelineMetrics {
             evictions_with_low_residence_duration: std::sync::RwLock::new(
                 evictions_with_low_residence_duration,
             ),
-        }
-    }
-}
+        };
 
-impl Drop for TimelineMetrics {
-    fn drop(&mut self) {
+        if fake {
+            m.remove_metrics();
+        }
+
+        m
+    }
+
+    fn remove_metrics(&self) {
         let tenant_id = &self.tenant_id;
         let timeline_id = &self.timeline_id;
         let _ = RECONSTRUCT_TIME.remove_label_values(&[tenant_id, timeline_id]);
@@ -860,6 +867,14 @@ impl Drop for TimelineMetrics {
     }
 }
 
+impl Drop for TimelineMetrics {
+    fn drop(&mut self) {
+        if !self.fake {
+            self.remove_metrics();
+        }
+    }
+}
+
 pub fn remove_tenant_metrics(tenant_id: &TenantId) {
     let tid = tenant_id.to_string();
     let _ = TENANT_SYNTHETIC_SIZE_METRIC.remove_label_values(&[&tid]);

pageserver/src/tenant/timeline.rs

@@ -1366,6 +1366,7 @@ impl Timeline {
                 ancestor_lsn: metadata.ancestor_lsn(),
 
                 metrics: TimelineMetrics::new(
+                    false,
                     &tenant_id,
                     &timeline_id,
                     crate::metrics::EvictionsWithLowResidenceDurationBuilder::new(