chore: instrument the cache layer (#942)

src/helpers/cache.ts

@@ -1,5 +1,6 @@
 import redis from '../redis';
 import { get, set } from '../aws';
+import { cacheActivitesCount } from '../metrics';
 
 export const VP_KEY_PREFIX = 'vp';
 
@@ -15,6 +16,7 @@ export async function cachedVp<Type extends Promise<VpResult>>(
   toCache = true
 ) {
   if (!toCache || !redis) {
+    cacheActivitesCount.inc({ type: 'vp', status: 'skip' });
     return { result: await callback(), cache: false };
   }
 
@@ -24,35 +26,42 @@ export async function cachedVp<Type extends Promise<VpResult>>(
     cache.vp = parseFloat(cache.vp);
     cache.vp_by_strategy = JSON.parse(cache.vp_by_strategy);
 
+    cacheActivitesCount.inc({ type: 'vp', status: 'hit' });
     return { result: cache as Awaited<Type>, cache: true };
   }
 
   const result = await callback();
+  let cacheHitStatus = 'unqualified';
 
   if (result.vp_state === 'final') {
+    cacheHitStatus = 'miss';
     const multi = redis.multi();
     multi.hSet(`${VP_KEY_PREFIX}:${key}`, 'vp', result.vp);
     multi.hSet(`${VP_KEY_PREFIX}:${key}`, 'vp_by_strategy', JSON.stringify(result.vp_by_strategy));
     multi.hSet(`${VP_KEY_PREFIX}:${key}`, 'vp_state', result.vp_state);
     multi.exec();
   }
 
+  cacheActivitesCount.inc({ type: 'vp', status: cacheHitStatus });
   return { result, cache: false };
 }
 
 export async function cachedScores<Type>(key: string, callback: () => Type, toCache = false) {
   if (!toCache || !!process.env.AWS_REGION) {
+    cacheActivitesCount.inc({ type: 'scores', status: 'skip' });
     return { scores: await callback(), cache: false };
   }
 
   const cache = await get(key);
 
   if (cache) {
+    cacheActivitesCount.inc({ type: 'scores', status: 'hit' });
     return { scores: cache as Awaited<Type>, cache: true };
   }
 
   const scores = await callback();
   set(key, scores);
 
+  cacheActivitesCount.inc({ type: 'scores', status: 'miss' });
   return { scores, cache: false };
 }

src/metrics.ts

@@ -30,3 +30,9 @@ export const requestDeduplicatorSize = new client.Gauge({
   name: 'request_deduplicator_size',
   help: 'Total number of items in the deduplicator queue'
 });
+
+export const cacheActivitesCount = new client.Gauge({
+  name: 'cache_activites_count',
+  help: 'Number of requests to the cache layer',
+  labelNames: ['type', 'status']
+});