Tuning and Monitoring RMAN and the Automatic Diagnostic Workflow - OCP: Oracle Database 12c Administrator Certified Professional - page 257

Monitoring RMAN Operations
More often than not, RMAN works just fine. However, there are times when you will want
to be able to monitor RMAN operations. In the next sections, we will discuss RMAN tun-
ing, including enabling asynchronous I/O and monitoring RMAN operations with data
dictionary views.
Configuring for Asynchronous I/O
In most cases, your operating system (OS) will already support asynchronous I/O operations
natively. In these cases, no special configuration is required.
If your OS does not support native asynchronous I/O operations, then you may want
to consider configuring your database, and RMAN, to simulate asynchronous I/O. Oracle
provides Oracle slave I/O processes, which are individual processes that Oracle starts that
are used to simulate asynchronous I/O.
You can enable these asynchronous I/O processes by configuring the parameter DBWR_
IO_SLAVES . This parameter indicates to Oracle how many I/O slaves should be started
when the database is started. When this parameter is zero, simulated asynchronous I/O
is disabled. When the parameter is greater than zero, Oracle will automatically start four
backup I/O slaves.
When using I/O slaves to simulate asynchronous I/O, you will also want to configure
the large pool using the LARGE_POOL_SIZE parameter. RMAN will use the large pool, if
configured, instead of the shared pool. If the large pool is allocated when you're using I/O
slaves but insufficient memory exists, then RMAN will generate an error and will not use
asynchronous I/O. If the large pool is not allocated and I/O slaves are enabled, RMAN will
use the shared pool and try to simulate asynchronous I/O operations. If the large pool is
not allocated and there is not enough shared-pool memory, then Oracle will use the PGA.
In this case, simulated asynchronous I/O operations will not occur.
Using the V$SESSION_LONGOPS View to Monitor RMAN
Oracle provides the V$SESSION_LONGOPS view as a means to monitor long-running pro-
cesses within the Oracle Database. Since RMAN uses internal database calls, records
for long-running RMAN operations will appear in V$SESSION_LONGOPS . This view can
be useful when you're trying to determine just how long a database backup or restore is
likely to take. In this example, you first start an RMAN backup in one session. And as
the backup is running, you will query the V$SESSION_LONGOPS view with this query:
SQL> Select sid, serial#, opname, time_remaining
2 From v$session_longops
3 Where sid in (select sid from v$session
4 Where program like '%rman%')
5 And time_remaining > 0;
SID SERIAL# OPNAME TIME_REMAINING
---------- ---------- ------------------------------ --------------
129 415 RMAN: aggregate input 188
121 269 RMAN: full datafile backup 161