Index: src/bp-core/admin/bp-core-admin-schema.php
===================================================================
--- src/bp-core/admin/bp-core-admin-schema.php
+++ src/bp-core/admin/bp-core-admin-schema.php
@@ -143,8 +143,7 @@
 				KEY type (type),
 				KEY mptt_left (mptt_left),
 				KEY mptt_right (mptt_right),
-				KEY hide_sitewide (hide_sitewide),
-				KEY is_spam (is_spam)
+				KEY component_type_user_id_date_recorded (component, type, user_id, date_recorded)
 			) {$charset_collate};";
 
 	$sql[] = "CREATE TABLE {$bp_prefix}bp_activity_meta (
Index: src/bp-core/bp-core-update.php
===================================================================
--- src/bp-core/bp-core-update.php
+++ src/bp-core/bp-core-update.php
@@ -268,6 +268,11 @@
 		if ( $raw_db_version < 11105 ) {
 			bp_update_to_2_7();
 		}
+
+		// Version 2.9.0.
+		if ( $raw_db_version < 11590 ) {
+			bp_update_to_2_9();
+		}
 	}
 
 	/* All done! *************************************************************/
@@ -313,6 +318,17 @@
 			}
 		}
 	}
+
+	// 2.9.0: Drop some activity indexes.
+	if ( $raw_db_version < 11590 ) {
+		$activity_db = bp_core_get_table_prefix() . 'bp_activity';
+		$wpdb->hide_errors();
+		if ( $wpdb->query( $wpdb->prepare( "SHOW TABLES LIKE %s", bp_esc_like( $activity_db ) ) ) ) {
+			$wpdb->query( "ALTER TABLE {$activity_db} DROP INDEX hide_sitewide" );
+			$wpdb->query( "ALTER TABLE {$activity_db} DROP INDEX is_spam" );
+		}
+		$wpdb->show_errors();
+	}
 }
 
 /** Upgrade Routines **********************************************************/
@@ -543,6 +559,17 @@
 }
 
 /**
+ * 2.9.0 update routine.
+ *
+ * - Add new index for activity DB table.
+ *
+ * @since 2.9.0
+ */
+function bp_update_to_2_9() {
+	bp_core_install_activity_streams();
+}
+
+/**
  * Updates the component field for new_members type.
  *
  * @since 2.2.0
Index: src/class-buddypress.php
===================================================================
--- src/class-buddypress.php
+++ src/class-buddypress.php
@@ -294,7 +294,7 @@
 		/** Versions **********************************************************/
 
 		$this->version    = '2.9.0-alpha';
-		$this->db_version = 11105;
+		$this->db_version = 11591;
 
 		/** Loading ***********************************************************/