diff --git a/src/upgrades/3.3.0/chat_room_refactor.js b/src/upgrades/3.3.0/chat_room_refactor.js
index 7c008a9764..0d9242b10c 100644
--- a/src/upgrades/3.3.0/chat_room_refactor.js
+++ b/src/upgrades/3.3.0/chat_room_refactor.js
@@ -1,8 +1,6 @@
 'use strict';
 
 
-const _ = require('lodash');
-
 const db = require('../../database');
 const batch = require('../../batch');
 
@@ -18,46 +16,69 @@ module.exports = {
 		for (let i = 1; i <= nextChatRoomId; i++) {
 			allRoomIds.push(i);
 		}
-		progress.total = allRoomIds.length;
+		progress.total = 0;
+
+		// calculate user count and set progress.total
+		await batch.processArray(allRoomIds, async (roomIds) => {
+			await Promise.all(roomIds.map(async (roomId) => {
+				const userCount = await db.sortedSetCard(`chat:room:${roomId}:uids`);
+				await db.setObjectField(`chat:room:${roomId}`, 'userCount', userCount);
+				progress.total += userCount;
+			}));
+		}, {
+			batch: 500,
+		});
+
 		await batch.processArray(allRoomIds, async (roomIds) => {
-			progress.incr(roomIds.length);
-			const [arrayOfUids, arrayOfRoomData] = await Promise.all([
-				db.getSortedSetsMembers(roomIds.map(roomId => `chat:room:${roomId}:uids`)),
-				db.getObjects(roomIds.map(roomId => `chat:room:${roomId}`)),
-			]);
+			const arrayOfRoomData = await db.getObjects(roomIds.map(roomId => `chat:room:${roomId}`));
 
 			await Promise.all(roomIds.map(async (roomId, index) => {
-				const uids = arrayOfUids[index];
 				const roomData = arrayOfRoomData[index];
-				if (!uids.length && !roomData) {
+				if (!roomData) {
 					return;
 				}
-				if (roomData && roomData.owner && !uids.includes(String(roomData.owner))) {
-					uids.push(roomData.owner);
-				}
-				const userKeys = uids.map(uid => `uid:${uid}:chat:room:${roomId}:mids`);
-				const mids = await db.getSortedSetsMembers(userKeys);
-				const uniqMids = _.uniq(_.flatten(mids));
-				let messageData = await db.getObjects(uniqMids.map(mid => `message:${mid}`));
-				messageData.forEach((m, idx) => {
-					if (m) {
-						m.mid = parseInt(uniqMids[idx], 10);
-					}
-				});
-				messageData = messageData.filter(Boolean);
 
-				const bulkSet = messageData.map(
-					msg => [`message:${msg.mid}`, { roomId: roomId }]
-				);
+				const midsSeen = Object.create(null);
+				await batch.processSortedSet(`chat:room:${roomId}:uids`, async (uids) => {
+					for (const uid of uids) {
+						// eslint-disable-next-line no-await-in-loop
+						await batch.processSortedSet(`uid:${uid}:chat:room:${roomId}:mids`, async (mids) => {
+							const uniqMids = mids.filter(mid => !midsSeen.hasOwnProperty(mid));
+							if (!uniqMids.length) {
+								return;
+							}
+
+							let messageData = await db.getObjects(uniqMids.map(mid => `message:${mid}`));
+							messageData.forEach((m, idx) => {
+								if (m) {
+									m.mid = parseInt(uniqMids[idx], 10);
+								}
+							});
+							messageData = messageData.filter(Boolean);
 
-				await db.setObjectBulk(bulkSet);
-				await db.setObjectField(`chat:room:${roomId}`, 'userCount', uids.length);
-				await db.sortedSetAdd(
-					`chat:room:${roomId}:mids`,
-					messageData.map(m => m.timestamp),
-					messageData.map(m => m.mid),
-				);
-				await db.deleteAll(userKeys);
+							const bulkSet = messageData.map(
+								msg => [`message:${msg.mid}`, { roomId: roomId }]
+							);
+
+							await db.setObjectBulk(bulkSet);
+							await db.sortedSetAdd(
+								`chat:room:${roomId}:mids`,
+								messageData.map(m => m.timestamp),
+								messageData.map(m => m.mid),
+							);
+							uniqMids.forEach((mid) => {
+								midsSeen[mid] = 1;
+							});
+						}, {
+							batch: 500,
+						});
+						// eslint-disable-next-line no-await-in-loop
+						await db.deleteAll(`uid:${uid}:chat:room:${roomId}:mids`);
+					}
+					progress.incr(uids.length);
+				}, {
+					batch: 500,
+				});
 			}));
 		}, {
 			batch: 500,