PATCH: Optimize Message Text Searches for from:Username

- Restrict the flexibility of our username search
	- Case-Sensitive only
	- Prefix, NOT substring
	- We still support multiple `from:` lines,
	  even though no one *ever* does that.
- Add index `{ rid: 1, ts: 1, 'u.username': 1 }`
	- Support the `from:Username` prefix query
	- Additionally, index the timestamp, since these searches
	  default to {ts:-1} and it is extremely rare that users
		customize away from that.  Conform to ESR.
- Change FTS index to `{ rid: 1, msg: 'text', 'u.username': 1 }`
	- Support the `from:Username` prefix query, albeit not as well
	  as the other index will.  (IXSCAN vs. B-Tree range)

apps/meteor/server/lib/parseMessageSearchQuery.ts

@@ -44,10 +44,8 @@ class MessageSearchQueryParser {
 			}
 			from.push(username);
 
-			this.query['u.username'] = {
-				$regex: from.join('|'),
-				$options: 'i',
-			};
+			// Search for case-sensitive prefix match (no substrings)
+			this.query['u.username'] = { $in: from.map((prefix) => RegExp(`^${prefix}`)) };
 
 			return '';
 		});

apps/meteor/server/models/raw/Messages.ts

@@ -53,7 +53,8 @@ export class MessagesRaw extends BaseRaw<IMessage> implements IMessagesModel {
 			{ key: { 'editedBy._id': 1 }, sparse: true },
 			{ key: { 'rid': 1, 't': 1, 'u._id': 1 } },
 			{ key: { expireAt: 1 }, expireAfterSeconds: 0 },
-			{ key: { rid: 1, msg: 'text' } },
+			{ key: { 'rid': 1, 'msg': 'text', 'u.username': 1 }, name: 'noach__rid_1_msg_text_u.username_1' },
+			{ key: { 'rid': 1, 'ts': 1, 'u.username': 1 }, name: 'noach__rid_1_ts_1_u.username_1' }, // Support `from:Username` searches (*sans* msg text terms)
 			{ key: { 'file._id': 1 }, sparse: true },
 			{ key: { 'mentions.username': 1 }, sparse: true },
 			{ key: { pinned: 1 }, sparse: true },
@@ -866,8 +867,8 @@ export class MessagesRaw extends BaseRaw<IMessage> implements IMessagesModel {
 	findForUpdates(roomId: string, timestamp: Date, options?: FindOptions<IMessage>): FindCursor<IMessage> {
 		// HACK: To support bulk username renames without causing massive load (due to fetching every ancient post),
 		// only fetch **recently created** messages.
-		const duration_30_days_in_ms = 30 * 24 * 60 * 60 * 1000
-		const date_30_days_ago = new Date(Date.now() - duration_30_days_in_ms)
+		const duration_30_days_in_ms = 30 * 24 * 60 * 60 * 1000;
+		const date_30_days_ago = new Date(Date.now() - duration_30_days_in_ms);
 
 		const query = {
 			rid: roomId,