Added comment related to aurora_read_replica_read_committed

lib/MySQL_Session.cpp

@@ -2454,6 +2454,13 @@ bool MySQL_Session::handler_again___status_SETTING_GENERIC_VARIABLE(int *_rc, co
  sprintf(query,q,"tx_isolation", var_value);
  }
  } else if (strncasecmp("aurora_read_replica_read_committed", var_name, 34) == 0) {
+ // If aurora_read_replica_read_committed is set, isolation level is
+ // internally reset so that it will be set again.
+ // This solves the weird behavior in AWS Aurora related to isolation level
+ // as described in
+ // https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Reference.html#AuroraMySQL.Reference.IsolationLevels
+ // Basically, to change isolation level you must first set
+ // aurora_read_replica_read_committed , and then isolation level
  MySQL_Connection *beconn = mybe->server_myds->myconn;
  if (beconn->var_hash[SQL_ISOLATION_LEVEL] != 0) {
  beconn->var_hash[SQL_ISOLATION_LEVEL] = 0;