fix: classify coalesced cache misses in PageGetExecutor

src/service/metrics.rs

@@ -129,7 +129,48 @@ pub fn fetch_request_pages(kind: &ObjectKind, pages: u16) {
         .observe(f64::from(pages));
 }
 
-pub fn page_request_count(kind: &ObjectKind, typ: &str) {
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum PageRequestType {
+    /// Total page requests observed by the service.
+    Access,
+    /// Page requests that fetched bytes from object storage.
+    Download,
+    /// Object storage fetches where a hedged request was issued.
+    Hedged,
+    /// Fetches whose primary attempt used the client-preferred bucket.
+    ClientPref,
+    /// Fetches that succeeded via a fallback bucket after the primary path failed.
+    Fallback,
+    /// Page requests that completed successfully, regardless of hit/miss path.
+    Success,
+    /// Aggregate cache-hit count (includes both memory and disk hits).
+    CacheHit,
+    /// Cache hits served from in-memory cache.
+    CacheHitMemory,
+    /// Cache hits served from disk cache.
+    CacheHitDisk,
+    /// Requests that waited on another in-flight miss for the same page instead of downloading.
+    Coalesced,
+}
+
+impl PageRequestType {
+    const fn as_label(self) -> &'static str {
+        match self {
+            Self::Access => "access",
+            Self::Download => "download",
+            Self::Hedged => "hedged",
+            Self::ClientPref => "client_pref",
+            Self::Fallback => "fallback",
+            Self::Success => "success",
+            Self::CacheHit => "cache_hit",
+            Self::CacheHitMemory => "cache_hit_memory",
+            Self::CacheHitDisk => "cache_hit_disk",
+            Self::Coalesced => "coalesced",
+        }
+    }
+}
+
+pub fn page_request_count(kind: &ObjectKind, typ: PageRequestType) {
     static COUNTER: LazyLock<IntCounterVec> = LazyLock::new(|| {
         register_int_counter_vec!(
             "cachey_page_request_total",
@@ -139,7 +180,7 @@ pub fn page_request_count(kind: &ObjectKind, typ: &str) {
         .unwrap()
     });
 
-    COUNTER.with_label_values(&[&**kind, typ]).inc();
+    COUNTER.with_label_values(&[&**kind, typ.as_label()]).inc();
 }
 
 pub fn page_download_latency(kind: &ObjectKind, latency: std::time::Duration) {