Tuning dataguard and RMAN

Session Data Unit

As we deal with wide area network (WAN) connectivity between the primary database and the standby database, we often have the need to adjust the session data unit (SDU) to gain additional performance and throughput. We will want to adjust the SDU when the transferred data is fragmented into separate packets or large amounts of data are being transferred.

/u01/app/oracle/product/11.2.0.3/dbhome_1/network/admin/sqlnet.ora

# -- This will set SDU to 32k for all the databases
# --
DEFAULT_SDU_SIZE=32767
TCP.NODELAY=YES

Block Change Tracking

If you are performing any level of incremental backups, you need to enable block change tracking (BCT) to track changed blocks on the database since the last backup. Enabling BCT will significantly reduce your backup window for incremental backups as RMAN leverages the BCT file to identify specific blocks that must be backed up

alter database enable block change tracking using file '+DATA_EXAP';

SQL> select filename, status, bytes from v$block_change_tracking;

image copy of the database again. Updated incremental backup image copies are essential when it comes to reducing restore times, deploying snapshot technology, and creating clones of production snapshot data.

Settings for RMAN Backups on the Exadata

With RMAN, we can perform image copy backups or backup set backups. More companies choose RMAN backup set implementations simply because this technology is what they are comfortable with. Instead, consider image copy backups with incremental updates on the Exadata and imagine a world where you do not have to perform a full backup again. Depending on which method we choose, we can tune the RMAN backup processes with the following hidden underscore (_) parameters:

 _backup_disk_bufcnt—number of buffers used to process backup sets

 _backup_disk_bufsz—size of the buffers used to process backup sets

 _backup_file_bufcnt—number of buffers used to process image copies

 _backup_file_bufsz—size of the buffers used to process image copies

Table 8.1 depicts the best-practice recommendations for the number of buffers and buffer size to perform backup sets and image copies for RMAN backups over IB or 10GigE connections to the Exadata over dNFS.

Table 8.1 RMAN Backup Settings

The following are additional recommended guidelines:

 Use two to four RMAN channels per tray of disks.

 Load-balance RMAN channels across shares and controllers.

 Load-balance RMAN channels across Exadata Compute Nodes.