Fix Bug#56340 innodb updates index stats too frequently after non-index updates

This is a manual merge from mysql-5.1-innodb of:

  revno: 3618
  revision-id: vasil.dimov@oracle.com-20100930124844-yglojy7c3vaji6dx
  parent: vasil.dimov@oracle.com-20100930102618-s9f9ytbytr3eqw9h
  committer: Vasil Dimov <vasil.dimov@oracle.com>
  branch nick: mysql-5.1-innodb
  timestamp: Thu 2010-09-30 15:48:44 +0300
  message:
    Fix Bug#56340 innodb updates index stats too frequently after non-index updates

    This is a simple optimization issue. All stats are related to only indexed
    columns, index size or number of rows in the whole table. UPDATEs that touch
    only non-indexed columns cannot affect stats and we can avoid calling the
    function row_update_statistics_if_needed() which may result in unnecessary I/O.

    Approved by:	Marko (rb://466)

In addition to the above message: we know that
row_update_cascade_for_mysql() (the other place where
row_update_statistics_if_needed is called) always updates indexed
columns (FK-related), so there is no need to add this cond there.

storage/innobase/row/row0mysql.c

@@ -1481,7 +1481,12 @@ run_again:
 		srv_n_rows_updated++;
 	}
 
-	row_update_statistics_if_needed(prebuilt->table);
+	/* We update table statistics only if it is a DELETE or UPDATE
+	that changes indexed columns, UPDATEs that change only non-indexed
+	columns would not affect statistics. */
+	if (node->is_delete || !(node->cmpl_info & UPD_NODE_NO_ORD_CHANGE)) {
+		row_update_statistics_if_needed(prebuilt->table);
+	}
 
 	trx->op_info = "";