Add cache metrics

src/metrics.ts

@@ -84,3 +84,23 @@ export const dbQueryDurationHistogram = new Histogram({
   name: 'ditto_db_query_duration_ms',
   help: 'Duration of database queries',
 });
+
+export const cachedFaviconsSizeGauge = new Gauge({
+  name: 'ditto_cached_favicons_size',
+  help: 'Number of domain favicons in cache',
+});
+
+export const cachedLnurlsSizeGauge = new Gauge({
+  name: 'ditto_cached_lnurls_size',
+  help: 'Number of LNURL details in cache',
+});
+
+export const cachedNip05sSizeGauge = new Gauge({
+  name: 'ditto_cached_nip05s_size',
+  help: 'Number of NIP-05 results in cache',
+});
+
+export const cachedLinkPreviewSizeGauge = new Gauge({
+  name: 'ditto_cached_link_previews_size',
+  help: 'Number of link previews in cache',
+});

src/utils/SimpleLRU.ts

@@ -1,6 +1,7 @@
 // deno-lint-ignore-file ban-types
 
 import { LRUCache } from 'lru-cache';
+import { type Gauge } from 'prom-client';
 
 type FetchFn<K extends {}, V extends {}, O extends {}> = (key: K, opts: O) => Promise<V>;
 
@@ -8,6 +9,10 @@ interface FetchFnOpts {
   signal?: AbortSignal | null;
 }
 
+type SimpleLRUOpts<K extends {}, V extends {}> = LRUCache.Options<K, V, void> & {
+  gauge?: Gauge;
+};
+
 export class SimpleLRU<
   K extends {},
   V extends {},
@@ -15,7 +20,7 @@ export class SimpleLRU<
 > {
   protected cache: LRUCache<K, V, void>;
 
-  constructor(fetchFn: FetchFn<K, V, { signal: AbortSignal }>, opts: LRUCache.Options<K, V, void>) {
+  constructor(fetchFn: FetchFn<K, V, { signal: AbortSignal }>, private opts: SimpleLRUOpts<K, V>) {
     this.cache = new LRUCache({
       fetchMethod: (key, _staleValue, { signal }) => fetchFn(key, { signal: signal as unknown as AbortSignal }),
       ...opts,
@@ -24,9 +29,13 @@ export class SimpleLRU<
 
   async fetch(key: K, opts?: O): Promise<V> {
     const result = await this.cache.fetch(key, opts);
+
+    this.opts.gauge?.set(this.cache.size);
+
     if (result === undefined) {
       throw new Error('SimpleLRU: fetch failed');
     }
+
     return result;
   }
 

src/utils/favicon.ts

@@ -2,6 +2,7 @@ import { DOMParser } from '@b-fuze/deno-dom';
 import Debug from '@soapbox/stickynotes/debug';
 import tldts from 'tldts';
 
+import { cachedFaviconsSizeGauge } from '@/metrics.ts';
 import { SimpleLRU } from '@/utils/SimpleLRU.ts';
 import { Time } from '@/utils/time.ts';
 import { fetchWorker } from '@/workers/fetch.ts';
@@ -37,7 +38,7 @@ const faviconCache = new SimpleLRU<string, URL>(
 
     throw new Error(`Favicon not found: ${key}`);
   },
-  { max: 500, ttl: Time.hours(1) },
+  { max: 500, ttl: Time.hours(1), gauge: cachedFaviconsSizeGauge },
 );
 
 export { faviconCache };

src/utils/lnurl.ts

@@ -1,6 +1,7 @@
 import { LNURL, LNURLDetails } from '@nostrify/nostrify/ln';
 import Debug from '@soapbox/stickynotes/debug';
 
+import { cachedLnurlsSizeGauge } from '@/metrics.ts';
 import { SimpleLRU } from '@/utils/SimpleLRU.ts';
 import { Time } from '@/utils/time.ts';
 import { fetchWorker } from '@/workers/fetch.ts';
@@ -20,7 +21,7 @@ const lnurlCache = new SimpleLRU<string, LNURLDetails>(
       throw e;
     }
   },
-  { max: 1000, ttl: Time.minutes(30) },
+  { max: 1000, ttl: Time.minutes(30), gauge: cachedLnurlsSizeGauge },
 );
 
 /** Get an LNURL from a lud06 or lud16. */

src/utils/nip05.ts

@@ -4,6 +4,7 @@ import Debug from '@soapbox/stickynotes/debug';
 import tldts from 'tldts';
 
 import { Conf } from '@/config.ts';
+import { cachedNip05sSizeGauge } from '@/metrics.ts';
 import { Storages } from '@/storages.ts';
 import { SimpleLRU } from '@/utils/SimpleLRU.ts';
 import { Time } from '@/utils/time.ts';
@@ -43,7 +44,7 @@ const nip05Cache = new SimpleLRU<string, nip19.ProfilePointer>(
       throw e;
     }
   },
-  { max: 500, ttl: Time.hours(1) },
+  { max: 500, ttl: Time.hours(1), gauge: cachedNip05sSizeGauge },
 );
 
 async function localNip05Lookup(store: NStore, localpart: string): Promise<nip19.ProfilePointer | undefined> {

src/utils/unfurl.ts

@@ -5,6 +5,7 @@ import { unfurl } from 'unfurl.js';
 
 import { Conf } from '@/config.ts';
 import { PreviewCard } from '@/entities/PreviewCard.ts';
+import { cachedLinkPreviewSizeGauge } from '@/metrics.ts';
 import { Time } from '@/utils/time.ts';
 import { fetchWorker } from '@/workers/fetch.ts';
 
@@ -67,6 +68,7 @@ function unfurlCardCached(url: string, signal = AbortSignal.timeout(1000)): Prom
   } else {
     const card = unfurlCard(url, signal);
     previewCardCache.set(url, card);
+    cachedLinkPreviewSizeGauge.set(previewCardCache.size);
     return card;
   }
 }