messages table: introduce new computed isStory field for index usage

ts/sql/migrations/46-optimize-stories.ts

@@ -0,0 +1,40 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { Database } from 'better-sqlite3';
+
+import type { LoggerType } from '../../types/Logging';
+
+export default function updateToSchemaVersion46(
+  currentVersion: number,
+  db: Database,
+  logger: LoggerType
+): void {
+  if (currentVersion >= 46) {
+    return;
+  }
+
+  db.transaction(() => {
+    db.exec(
+      `
+      --- Add column to messages table
+
+      ALTER TABLE messages
+      ADD COLUMN
+      isStory INTEGER
+      GENERATED ALWAYS
+      AS (type = 'story');
+
+      --- Update important message indices
+
+      DROP INDEX   messages_conversation;
+      CREATE INDEX messages_conversation ON messages
+        (conversationId, isStory, storyId, received_at, sent_at);
+      `
+    );
+
+    db.pragma('user_version = 46');
+  })();
+
+  logger.info('updateToSchemaVersion46: success!');
+}