From ec35b291eee9c185e1ce03f3900eebb296f84b8e Mon Sep 17 00:00:00 2001
From: you <you@example.com>
Date: Sun, 29 Mar 2026 14:06:29 +0000
Subject: [PATCH] fix: cache hit rate excludes stale hits + debounce
 bulk-health invalidation
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Two cache bugs fixed:

1. Hit rate formula excluded stale hits — reported rate was artificially low
   because stale-while-revalidate responses (which ARE cache hits from the
   caller's perspective) were not counted. Changed formula from
   hits/(hits+misses) to (hits+staleHits)/(hits+staleHits+misses).

2. Bulk-health cache invalidated on every advert packet — in a mesh with
   dozens of nodes advertising every few seconds, this caused the expensive
   bulk-health query to be recomputed on nearly every request, defeating
   the cache entirely. Switched to 30s debounced invalidation via
   debouncedInvalidateBulkHealth().

Added regression test for hit rate formula in test-server-routes.js.
---
 server.js             | 13 ++++++++++---
 test-server-routes.js | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/server.js b/server.js
index 4962c213..0a3c652d 100644
--- a/server.js
+++ b/server.js
@@ -207,6 +207,13 @@ class TTLCache {
       if (key.startsWith(prefix)) this.store.delete(key);
     }
   }
+  debouncedInvalidateBulkHealth() {
+    if (this._bulkHealthTimer) return;
+    this._bulkHealthTimer = setTimeout(() => {
+      this._bulkHealthTimer = null;
+      this.invalidate('bulk-health');
+    }, 30000);
+  }
   debouncedInvalidateAll() {
     if (this._debounceTimer) return;
     this._debounceTimer = setTimeout(() => {
@@ -410,7 +417,7 @@ app.get('/api/perf', (req, res) => {
     avgMs: perfStats.requests ? Math.round(perfStats.totalMs / perfStats.requests * 10) / 10 : 0,
     endpoints: Object.fromEntries(sorted),
     slowQueries: perfStats.slowQueries.slice(-20),
-    cache: { size: cache.size, hits: cache.hits, misses: cache.misses, staleHits: cache.staleHits, recomputes: cache.recomputes, hitRate: cache.hits + cache.misses > 0 ? Math.round(cache.hits / (cache.hits + cache.misses) * 1000) / 10 : 0 },
+    cache: { size: cache.size, hits: cache.hits, misses: cache.misses, staleHits: cache.staleHits, recomputes: cache.recomputes, hitRate: cache.hits + cache.staleHits + cache.misses > 0 ? Math.round((cache.hits + cache.staleHits) / (cache.hits + cache.staleHits + cache.misses) * 1000) / 10 : 0 },
     packetStore: pktStore.getStats(),
     sqlite: (() => {
       try {
@@ -519,7 +526,7 @@ app.get('/api/health', (req, res) => {
       misses: cache.misses,
       staleHits: cache.staleHits,
       recomputes: cache.recomputes,
-      hitRate: cache.hits + cache.misses > 0 ? Math.round(cache.hits / (cache.hits + cache.misses) * 1000) / 10 : 0,
+      hitRate: cache.hits + cache.staleHits + cache.misses > 0 ? Math.round((cache.hits + cache.staleHits) / (cache.hits + cache.staleHits + cache.misses) * 1000) / 10 : 0,
     },
     websocket: {
       clients: wsClients,
@@ -723,7 +730,7 @@ for (const source of mqttSources) {
             // Invalidate this node's caches on advert
             cache.invalidate('node:' + p.pubKey);
             cache.invalidate('health:' + p.pubKey);
-            cache.invalidate('bulk-health');
+            cache.debouncedInvalidateBulkHealth();
 
             // Cross-reference: if this node's pubkey matches an existing observer, backfill observer name
             if (p.name && p.pubKey) {
diff --git a/test-server-routes.js b/test-server-routes.js
index 724ed1c0..d1f448d5 100644
--- a/test-server-routes.js
+++ b/test-server-routes.js
@@ -1254,6 +1254,24 @@ seedTestData();
     lastPathSeenMap.delete(liveNode);
   });
 
+  // ── Cache hit rate includes stale hits ──
+  await t('Cache hitRate includes staleHits in formula', async () => {
+    cache.clear();
+    cache.hits = 0;
+    cache.misses = 0;
+    cache.staleHits = 0;
+    // Simulate: 3 hits, 2 stale hits, 5 misses => rate = (3+2)/(3+2+5) = 50%
+    cache.hits = 3;
+    cache.staleHits = 2;
+    cache.misses = 5;
+    const r = await request(app).get('/api/health').expect(200);
+    assert(r.body.cache.hitRate === 50, 'hitRate should be (hits+staleHits)/(hits+staleHits+misses) = 50%, got ' + r.body.cache.hitRate);
+    // Reset
+    cache.hits = 0;
+    cache.misses = 0;
+    cache.staleHits = 0;
+  });
+
   // ── Summary ──
   console.log(`\n═══ Server Route Tests: ${passed} passed, ${failed} failed ═══`);
   if (failed > 0) process.exit(1);