CHAPTER 6. Improving Performance

Multiplexing Files
Parallel Operations

This chapter describes the performance-enhancing features available in the Enterprise Backup Utility.

The topics covered in this chapter are:

Multiplexing Files

Parallel Operations

Multiplexing Files

By default, each target database datafile is backed up in its own Backup File Set (BFS). If a backup media device is faster than disk access, a BFS consisting of a single database file may be unable to keep up with it. Under these circumstances, you may be able to improve backup performance by interlacing database blocks from database files stored on different physical disk drives into a single BFS. This practice is called multiplexing. Up to 32 files can be multiplexed into a single BFS.

Multiplexing effectively increases disk access speed by allowing data from multiple disks to be read into a single BFS simultaneously. Data blocks from the multiple datafiles are integrated into a single data stream to be fed to a media device. The Enterprise Backup Utility automatically demultiplexes the BFS upon restore.

To use the multiplexing feature of the Enterprise Backup Utility, use the mux specifier in your command script. By default, files are backed up without multiplexing.

You cannot multiplex control, parameter, or archived log files.

Note: Use multiplexing only if the media device is so fast that it is not streaming continuously in the default (no multiplexing) case. Multiplexing to an already fully-utilized media device not only fails to improve performance, but may even degrade it.

Figure 6 - 1 depicts a no-multiplex backup of a tablespace with four datafiles, stored across four physical devices. Each datafile is backed up to tape in its own BFS, and the BFSs are written to tape sequentially.

Figure 6 - 1. Backing Up a Tablespace without Multiplexing

Figure 6 - 2 depicts backing up the same tablespace backup as in Figure 6 - 1, with multiplexing. The datafiles are multiplexed in pairs, and each pair is written to a single BFS. Disk access speed is effectively doubled, allowing it to more closely match the speed of the backup media device.

Note: Only multiplex files from different drives. Do not multiplex files from the same drive.

Figure 6 - 2. Backing Up a Tablespace with Multiplexing

Example

Command script using mux specifier

# tablespace A contains "?/dbs/a[1-4].dbf"
backup online 
db_name = "PROD"
oracle_sid = "PROD" 
control_file 
tablespace = "A" 
mux = ("home/oracle/dbs/a1.dbf",  "/home/oracle/dbs/a2.dbf"),  ("/home/oracle/dbs/a3.dbf",  "/home/oracle/dbs/a4.dbf")

The mux specifier is used only to specify multiplexing of files identified by the database or tablespace or dbfile specifiers. It is not a substitute for the database or tablespace or dbfile specifiers. For example, if you do not specify tablespace="A" in the preceding example, an error results because the files ?/dbs/a[1-4].dbf are not in the backup set.

Parallel Operations

Another way to increase throughput to backup devices is to create parallel I/O streams. To use this feature, set the parallel specifier in your command scripts to the desired number of I/O streams. By default, the utility uses only one data stream.

You should set the parallel specifier equal to the number of devices available, as configured in your media management software. Setting parallel higher than the number of available devices degrades performance

Additional Information: See Also: See the "Backup" and "Restore" sections of Appendix A for the syntax for the parallel specifier.

Multi-Database Backup/Restore

Multiple databases can be backed up or restored simultaneously by invoking multiple obackup processes. Each backup or restore operation has its own obackup control process, but all obackup instances should access the same Backup Catalog and media management software. On a given host, concurrent instances of obackup with the same owner share an Instance Manager. Instances running under different oracle owners or on separate hosts must have their own Instance Managers.

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