connect to "localhost" fails when libmysqlclient db-plugin is used

[Vlad Lesin]

Percona-playback uses mysql_real_connect() to connect to server with the following way:

bool MySQLDBThread::connect()
{
  mysql_init(&handle);
  if (!mysql_real_connect(&handle,
                          options->host.c_str(),
                          options->user.c_str(),
                          options->password.c_str(),
                          options->schema.c_str(),
                          options->port,
                          "",
                          CLIENT_MULTI_STATEMENTS))
  {
    fprintf(stderr, "Can't connect to server: %s\n",
            mysql_error(&handle));
    return false;
  }
  return true;
}

If options->host is "localhost" mysql_real_connect() tries to connect to server via unix socket (or other ways to optimize communication on localhost, see documentation). In this case the name of unix socket must me specified in the pre-last argument of mysql_real_connect() which is empty string in the code above.

That is why if --mysql-host command line option is "localhost" percona-playback can not connect to server. The workaround is to use 127.0.0.1 instead of "localhost".