Add translation cache metrics, let the cache be configurable

src/caches/translationCache.ts

@@ -1,16 +1,11 @@
 import { LanguageCode } from 'iso-639-1';
 import { LRUCache } from 'lru-cache';
 
+import { Conf } from '@/config.ts';
 import { MastodonTranslation } from '@/entities/MastodonTranslation.ts';
-import { Time } from '@/utils/time.ts';
-
-/** Entity returned by DittoTranslator and LRUCache */
-interface DittoTranslation {
-  data: MastodonTranslation;
-}
 
 /** Translations LRU cache. */
-export const translationCache = new LRUCache<`${LanguageCode}-${string}`, DittoTranslation>({
+export const translationCache = new LRUCache<`${LanguageCode}-${string}`, MastodonTranslation>({
-  max: 1000,
+  max: Conf.caches.translation.max,
-  ttl: Time.hours(6),
+  ttl: Conf.caches.translation.ttl,
 });

src/config.ts

@@ -314,6 +314,13 @@ class Conf {
         ttl: Number(Deno.env.get('DITTO_CACHE_LINK_PREVIEW_TTL') || 12 * 60 * 60 * 1000),
       };
     },
+    /** Translation cache settings. */
+    get translation(): { max: number; ttl: number } {
+      return {
+        max: Number(Deno.env.get('DITTO_CACHE_TRANSLATION_MAX') || 1000),
+        ttl: Number(Deno.env.get('DITTO_CACHE_TRANSLATION_TTL') || 6 * 60 * 60 * 1000),
+      };
+    },
   };
 }
 

src/controllers/api/translate.ts

@@ -4,6 +4,7 @@ import { z } from 'zod';
 import { AppController } from '@/app.ts';
 import { translationCache } from '@/caches/translationCache.ts';
 import { MastodonTranslation } from '@/entities/MastodonTranslation.ts';
+import { cachedTranslationsSizeGauge } from '@/metrics.ts';
 import { getEvent } from '@/queries.ts';
 import { localeSchema } from '@/schema.ts';
 import { parseBody } from '@/utils/api.ts';
@@ -50,7 +51,7 @@ const translateController: AppController = async (c) => {
   const cached = translationCache.get(cacheKey);
 
   if (cached) {
-    return c.json(cached.data, 200);
+    return c.json(cached, 200);
   }
 
   const mediaAttachments = status?.media_attachments.map((value) => {
@@ -131,7 +132,9 @@ const translateController: AppController = async (c) => {
 
     mastodonTranslation.detected_source_language = data.source_lang;
 
-    translationCache.set(cacheKey, { data: mastodonTranslation });
+    translationCache.set(cacheKey, mastodonTranslation);
+    cachedTranslationsSizeGauge.set(translationCache.size);
+
     return c.json(mastodonTranslation, 200);
   } catch (e) {
     if (e instanceof Error && e.message.includes('not supported')) {

src/metrics.ts

@@ -121,6 +121,11 @@ export const cachedLinkPreviewSizeGauge = new Gauge({
   help: 'Number of link previews in cache',
 });
 
+export const cachedTranslationsSizeGauge = new Gauge({
+  name: 'ditto_cached_translations_size',
+  help: 'Number of translated statuses in cache',
+});
+
 export const internalSubscriptionsSizeGauge = new Gauge({
   name: 'ditto_internal_subscriptions_size',
   help: "Number of active subscriptions to Ditto's internal relay",