diff --git a/javascript/gallery.js b/javascript/gallery.js
index d3d8825dc..028f622c1 100644
--- a/javascript/gallery.js
+++ b/javascript/gallery.js
@@ -22,7 +22,19 @@ const el = {
 const SUPPORTED_EXTENSIONS = ['jpg', 'jpeg', 'png', 'webp', 'tiff', 'jp2', 'jxl', 'gif', 'mp4', 'mkv', 'avi', 'mjpeg', 'mpg', 'avr'];
 
 async function awaitForIDB(num = 0) {
-  while (outstanding > num || idbIsCleaning) await new Promise((resolve) => setTimeout(resolve, 50)); // eslint-disable-line no-promise-executor-return
+  while (outstanding > num || idbIsCleaning) await new Promise((resolve) => { setTimeout(resolve, 50); });
+}
+
+async function awaitForGallery(folderName, num = 0) {
+  let timeout = 0;
+  const timeoutThreshold = 60; // 30 seconds (60*0.5)
+  while (galleryHashes.size < num && activeGalleryFolder === folderName && !idbIsCleaning && timeout++ < timeoutThreshold) await new Promise((resolve) => { setTimeout(resolve, 500); }); // longer interval because it's a low priority check
+  if (timeout >= timeoutThreshold) {
+    throw new Error('Timed out waiting for gallery to populate');
+  }
+  if (idbIsCleaning) {
+    throw new Error('Another thread has already started cleaning the database');
+  }
 }
 
 // HTML Elements
@@ -554,9 +566,21 @@ async function gallerySort(btn) {
   updateStatusWithSort(`${arr.length.toLocaleString()} images | ${Math.floor(t1 - t0).toLocaleString()}ms`);
 }
 
+/**
+ * Function for updating the cleaning overlay message
+ * @callback updateMsgCallback
+ * @param {number} progressPercent - Value for completion progress percentage
+ * @returns {void}
+ */
+/**
+ * Function for removing the cleaning overlay
+ * @callback clearMsgCallback
+ * @returns {void}
+ */
+
 /**
  * Generate and display the overlay to announce cleanup is in progress.
- * @returns {() => void} Function for clearing the overlay
+ * @returns {[updateMsgCallback, clearMsgCallback]}
  */
 function showCleaningMsg() {
   const parent = el.folders.parentElement;
@@ -567,36 +591,54 @@ function showCleaningMsg() {
   parent.style.position = 'relative';
   cleaningOverlay.style.cssText = 'position: absolute; height: 100%; width: 100%; background-color: hsl(210 50 20 / 0.8); display: flex; align-items: center; justify-content: center;';
   msg.style.cssText = 'display: block; background-color: hsl(0 0 10); color: white; padding: 12px; border-radius: 8px; margin-right: 16px;';
-  msg.innerText = 'Running thumbnail cleanup';
+  msg.innerText = 'Thumbnail cleanup (0%)';
   anim.classList.add('idbBusyAnim');
 
   cleaningOverlay.append(msg, anim);
   parent.append(cleaningOverlay);
-  return () => {
-    parent.style.position = '';
-    cleaningOverlay.remove();
-  };
+  return [
+    (pct) => {
+      msg.innerText = `Thumbnail cleanup (${pct}%)`;
+    },
+    () => {
+      parent.style.position = '';
+      cleaningOverlay.remove();
+    },
+  ];
 }
 
-async function thumbCacheCleanup() {
+/**
+ * IndexedDB thumbnail cache cleanup function
+ * @param {string} folder - Folder to clean
+ * @param {number} imgCount - Expected number of images in gallery
+ */
+async function thumbCacheCleanup(folder, imgCount) {
   if (idbIsCleaning) return;
   await awaitForIDB();
-  idbIsCleaning = true;
-
-  const t0 = performance.now();
-  const cachedHashesCount = await idbCount()
-    .catch(() => 0);
-  if (cachedHashesCount < galleryHashes.size + 500) {
-    // Don't run when there aren't many excess entries
-    idbIsCleaning = false;
+  try {
+    await awaitForGallery(folder, imgCount);
+  } catch (err) {
+    log('Thumbnail DB cleanup:', err.message);
     return;
   }
+  if (activeGalleryFolder !== folder || idbIsCleaning) return; // First check for other thread activity
 
-  const removeOverlayFunc = showCleaningMsg();
-  idbClean(galleryHashes, activeGalleryFolder)
-    .then((delcount, folder) => {
+  const t0 = performance.now();
+  const staticGalleryHashes = new Set(galleryHashes);
+  const cachedHashesCount = await idbCount(folder)
+    .catch(() => 0);
+  if (cachedHashesCount < staticGalleryHashes.size + 500) {
+    // Don't run when there aren't many excess entries
+    return;
+  }
+  if (activeGalleryFolder !== folder || idbIsCleaning) return; // Second check for other thread activity
+
+  idbIsCleaning = true;
+  const [updateCleaningMsg, removeOverlayFunc] = showCleaningMsg();
+  idbClean(staticGalleryHashes, folder, updateCleaningMsg)
+    .then((delcount) => {
       const t1 = performance.now();
-      log(`Thumbnail DB cleanup: folder=${folder} kept=${galleryHashes.size} deleted=${delcount} time=${Math.floor(t1 - t0)}ms`);
+      log(`Thumbnail DB cleanup: folder=${folder} kept=${staticGalleryHashes.size} deleted=${delcount} time=${Math.floor(t1 - t0)}ms`);
     })
     .catch((err) => {
       error('Thumbnail DB cleanup: Cleanup failed.', err.message);
@@ -633,27 +675,25 @@ async function fetchFilesHT(evt) {
   el.files.appendChild(fragment);
 
   const t1 = performance.now();
-  activeGalleryFolder = evt.target.name;
   log(`gallery: folder=${evt.target.name} num=${numFiles} time=${Math.floor(t1 - t0)}ms`);
   updateStatusWithSort(`Folder: ${evt.target.name} | ${numFiles.toLocaleString()} images | ${Math.floor(t1 - t0).toLocaleString()}ms`);
-  addSeparators();
-  thumbCacheCleanup();
+  thumbCacheCleanup(evt.target.name, numFiles);
 }
 
 async function fetchFilesWS(evt) { // fetch file-by-file list over websockets
-  if (idbIsCleaning) return;
+  if (idbIsCleaning || !url) return;
   galleryHashes.clear(); // Only called here because fetchFilesHT isn't called directly
   el.files.innerHTML = '';
-  if (!url) return;
   if (ws && ws.readyState === WebSocket.OPEN) ws.close(); // abort previous request
   let wsConnected = false;
   try {
     ws = new WebSocket(`${url}/sdapi/v1/browser/files`);
-    wsConnected = await wsConnect(ws);
+    wsConnected = await wsConnect(ws); // Warning. This changes "evt".
   } catch (err) {
     log('gallery: ws connect error', err);
     return;
   }
+  activeGalleryFolder = evt.target.name;
   log(`gallery: connected=${wsConnected} state=${ws?.readyState} url=${ws?.url}`);
   if (!wsConnected) {
     await fetchFilesHT(evt); // fallback to http
@@ -688,11 +728,10 @@ async function fetchFilesWS(evt) { // fetch file-by-file list over websockets
   ws.onclose = (event) => {
     el.files.appendChild(fragment);
     // gallerySort();
-    activeGalleryFolder = evt.target.name;
     log(`gallery: folder=${evt.target.name} num=${numFiles} time=${Math.floor(t1 - t0)}ms`);
     updateStatusWithSort(`Folder: ${evt.target.name} | ${numFiles.toLocaleString()} images | ${Math.floor(t1 - t0).toLocaleString()}ms`);
     addSeparators();
-    thumbCacheCleanup();
+    thumbCacheCleanup(evt.target.name, numFiles);
   };
   ws.onerror = (event) => {
     log('gallery ws error', event);
diff --git a/javascript/indexdb.js b/javascript/indexdb.js
index ee84cde12..490eb46f6 100644
--- a/javascript/indexdb.js
+++ b/javascript/indexdb.js
@@ -1,9 +1,12 @@
-let db;
+/**
+ * @type {?IDBDatabase}
+ */
+let db = null;
 
 async function initIndexDB() {
   async function createDB() {
     return new Promise((resolve, reject) => {
-      const request = indexedDB.open('SDNext');
+      const request = indexedDB.open('SDNext', 2);
       request.onerror = (evt) => reject(evt);
       request.onsuccess = (evt) => {
         db = evt.target.result;
@@ -16,9 +19,15 @@ async function initIndexDB() {
       };
       request.onupgradeneeded = (evt) => {
         db = evt.target.result;
-        const store = db.createObjectStore('thumbs', { keyPath: 'hash' });
-        store.createIndex('hash', 'hash', { unique: true });
-        const index = store.index('hash');
+        const oldver = evt.oldVersion;
+        if (oldver < 1) {
+          const store = db.createObjectStore('thumbs', { keyPath: 'hash' });
+          store.createIndex('hash', 'hash', { unique: true });
+        }
+        if (oldver < 2) {
+          const existingStore = request.transaction.objectStore('thumbs');
+          existingStore.createIndex('folder', 'folder', { unique: false });
+        }
         resolve();
       };
     });
@@ -75,54 +84,81 @@ async function put(record) {
   });
 }
 
-async function idbGetAllKeys() {
+async function idbGetAllKeys(index = null, query = null) {
   if (!db) return null;
   return new Promise((resolve, reject) => {
-    const request = db
+    let request;
+    const store = db
       .transaction('thumbs', 'readonly')
-      .objectStore('thumbs')
-      .getAllKeys();
+      .objectStore('thumbs');
+    if (index) {
+      request = store.index(index).getAllKeys(query);
+    } else {
+      request = store.getAllKeys(query);
+    }
     request.onsuccess = () => resolve(request.result);
     request.onerror = (evt) => reject(evt);
   });
 }
 
-async function idbCount() {
+async function idbCount(folder = null) {
   if (!db) return null;
   return new Promise((resolve, reject) => {
-    const request = db
+    let request;
+    const store = db
       .transaction('thumbs', 'readonly')
-      .objectStore('thumbs')
-      .count();
+      .objectStore('thumbs');
+    if (folder) {
+      request = store.index('folder').count(folder);
+    } else {
+      request = store.count();
+    }
     request.onsuccess = () => resolve(request.result);
     request.onerror = (evt) => reject(evt);
   });
 }
 
-async function idbClean(keepSet, folder = null) {
+/**
+ * @param {Set<string>} keepSet - Set containing the hashes of the current files in the folder.
+ * @param {string} folder - Folder name/path
+ * @param {updateMsgCallback} msgCallback - Callback for updating progress display
+ */
+async function idbClean(keepSet, folder, msgCallback) {
   if (!db) return null;
   if (!(keepSet instanceof Set)) {
     throw new TypeError('IndexedDB cleaning function must be given a Set() of hashes to keep');
   }
-  if (folder === null) {
+  if (!folder) {
     throw new Error('IndexedDB cleaning function must be told the current active folder');
   }
+  const folderCached = new Set(await idbGetAllKeys('folder', folder));
+  const removals = folderCached.difference(keepSet);
+  const totalRemovals = removals.size;
+  let counter = 0;
   return new Promise((resolve, reject) => {
-    let counter = 0;
-    const request = db
+    const folderIndex = db
       .transaction('thumbs', 'readwrite')
       .objectStore('thumbs')
-      .openCursor();
+      .index('folder');
+    const request = folderIndex.openCursor(folder);
+
     request.onsuccess = (evt) => {
       const cursor = evt.target.result;
       if (cursor) {
-        if (folder === cursor.value.folder && !keepSet.has(cursor.key)) {
-          cursor.delete();
+        if (removals.has(cursor.primaryKey)) {
           counter++;
+          cursor.delete();
+        }
+        if (counter === totalRemovals) {
+          resolve(counter); // Got lucky with element order and can stop early
+        } else {
+          if (counter % 100 === 0 && counter !== 0) {
+            msgCallback(Math.floor((counter / totalRemovals) * 100));
+          }
+          cursor.continue();
         }
-        cursor.continue();
       } else {
-        resolve(counter, folder);
+        resolve(counter);
       }
     };
     request.onerror = (evt) => reject(evt);