add thumbnail data caching

src/lib/server/db.ts

@@ -68,6 +68,11 @@ type Migration = {
   statement: string;
 };
 const db: sqlite3.Database = new sqlite3.cached.Database('moshingmammut.db');
+const maxThumbnailCacheSize = 100;
+const maxThumbnailCacheAge = 1 * 60 * 60 * 1000; //1h in ms
+const thumbnailCache = new Map<string, { data: SongThumbnailImage[]; ts: number }>();
+let thumbnailCacheHits = 0;
+let thumbnailCacheMisses = 0;
 
 export function close() {
   try {
@@ -803,6 +808,7 @@ async function getPostsInternal(
     .flatMap((x) => x)
     .map((x) => x.thumbnailUrl)
     .filter((x) => x !== undefined)
+    .filter((x) => getCachedThumbnail(x) === null)
     .toArray();
   if (turls) {
     const tMap = await getSongThumbnailData('?, '.repeat(turls.length).slice(0, -2), turls);
@@ -811,7 +817,11 @@ async function getPostsInternal(
         if (songInfo.thumbnailUrl === undefined) {
           continue;
         }
-        const thumbs = tMap.get(songInfo.thumbnailUrl) ?? [];
+        let thumbs = getCachedThumbnail(songInfo.thumbnailUrl);
+        if (thumbs === null) {
+          thumbs = tMap.get(songInfo.thumbnailUrl) ?? [];
+          cacheThumbnail(songInfo.thumbnailUrl, thumbs);
+        }
         songInfo.resizedThumbnails = thumbs;
       }
     }
@@ -969,6 +979,73 @@ export async function getSongThumbnails(song: SongInfo): Promise<SongThumbnailIm
   if (!song.thumbnailUrl) {
     return [];
   }
+  const cachedThumbnail = getCachedThumbnail(song.thumbnailUrl);
+  if (cachedThumbnail !== null) {
+    return cachedThumbnail;
+  }
   const rows = await getSongThumbnailData('?', [song.thumbnailUrl]);
-  return rows.get(song.thumbnailUrl) ?? [];
+  const data = rows.get(song.thumbnailUrl) ?? [];
+  cacheThumbnail(song.thumbnailUrl, data);
+  return data;
+}
+
+function getCachedThumbnail(thumbnailUrl: string): SongThumbnailImage[] | null {
+  const cachedThumbnail = thumbnailCache.get(thumbnailUrl);
+  if (cachedThumbnail == undefined) {
+    thumbnailCacheMisses++;
+    return null;
+  }
+  const age = new Date().getTime() - cachedThumbnail.ts;
+  if (age <= maxThumbnailCacheAge) {
+    thumbnailCacheHits++;
+    return cachedThumbnail.data;
+  }
+  thumbnailCache.delete(thumbnailUrl);
+  thumbnailCacheMisses++;
+  return null;
+}
+
+function cacheThumbnail(thumbnailUrl: string, thumbnails: SongThumbnailImage[]) {
+  const now = new Date().getTime();
+  const initialSize = thumbnailCache.size;
+  if (initialSize >= maxThumbnailCacheSize) {
+    logger.debug('Sweeping cache. Current size', initialSize);
+    const deleteTimestampsOlderThan =
+      thumbnailCache
+        .values()
+        .map((x) => x.ts)
+        .toArray()
+        .sort((a, b) => a - b)
+        .slice(0, 20)
+        .pop() ?? 0;
+    const timestampExpired = now - maxThumbnailCacheAge;
+    const threshold = Math.max(timestampExpired, deleteTimestampsOlderThan);
+    thumbnailCache.forEach((v, k) => {
+      if (v.ts <= threshold) {
+        thumbnailCache.delete(k);
+      }
+    });
+    if (Logger.isDebugEnabled()) {
+      logger.debug(
+        'Swept cache. New size',
+        thumbnailCache.size,
+        'deleted',
+        initialSize - thumbnailCache.size,
+        'entries'
+      );
+      logger.debug(
+        'Current hitrate',
+        thumbnailCacheHits,
+        '/',
+        thumbnailCacheHits + thumbnailCacheMisses,
+        '=',
+        ((100.0 * thumbnailCacheHits) / (thumbnailCacheHits + thumbnailCacheMisses)).toFixed(2),
+        '%'
+      );
+    }
+  }
+  thumbnailCache.set(thumbnailUrl, {
+    data: thumbnails,
+    ts: now
+  });
 }