Limit the parallelism of AP object processing (#4193)

src/remote/activitypub/models/person.ts

@@ -1,4 +1,5 @@
 import * as mongo from 'mongodb';
+import * as promiseLimit from 'promise-limit';
 import { toUnicode } from 'punycode';
 
 import config from '../../../config';
@@ -21,7 +22,7 @@ import { ITag, extractHashtags } from './tag';
 import Following from '../../../models/following';
 import { IIdentifier } from './identifier';
 import { apLogger } from '../logger';
-
+import { INote } from '../../../models/note';
 const logger = apLogger;
 
 /**
@@ -494,10 +495,11 @@ export async function updateFeatured(userId: mongo.ObjectID) {
 	if (!Array.isArray(items)) throw new Error(`Collection items is not an array`);
 
 	// Resolve and regist Notes
+	const limit = promiseLimit(2);
 	const featuredNotes = await Promise.all(items
 		.filter(item => item.type === 'Note')
 		.slice(0, 5)
-		.map(item => resolveNote(item, resolver)));
+		.map(item => limit(() => resolveNote(item, resolver)) as Promise<INote>));
 
 	await User.update({ _id: user._id }, {
 		$set: {