Enable the real-time apply in 10G

If you want the redo data to be applied as it is received without waiting for the current standby redo log file to be archived, enable the real-time apply.

To start real-time apply:
SQL> alter database recover managed standby database using current logfile disconnect;

But Maybe you will encourter the error like this:

SQL> startup mount;
ORACLE instance started.

Total System Global Area  196681728 bytes
Fixed Size                  1298836 bytes
Variable Size             104861292 bytes
Database Buffers           83886080 bytes
Redo Buffers                6635520 bytes
Database mounted.
SQL> alter database recover managed standby database using current logfile disconnect;
alter database recover managed standby database using current logfile disconnect;

*
ERROR at line 1:
ORA-01153: an incompatible media recovery is active

Use the following command to close the process first.

SQL> alter database recover managed standby database cancel
  2  ;

Database altered.
You can view if the recover process is kicked off.
SQL> SELECT PROCESS, STATUS, THREAD#, SEQUENCE#, BLOCK#, BLOCKS
  2  FROM V$MANAGED_STANDBY;

PROCESS   STATUS          THREAD#  SEQUENCE#     BLOCK#     BLOCKS
--------- ------------ ---------- ---------- ---------- ----------
ARCH      CONNECTED             0          0          0          0
ARCH      CLOSING               1         59          1        246
ARCH      CONNECTED             0          0          0          0
ARCH      CONNECTED             0          0          0          0
MRP0      WAIT_FOR_LOG          1         60          0          0
RFS       IDLE                  1         60        827          6
RFS       IDLE                  0          0          0          0
RFS       IDLE                  0          0          0          0
RFS       IDLE                  0          0          0          0

9 rows selected.