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Chapter 16Tuning RMAN

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Background

One of the hardest chapters to develop material for

Tuning RMAN can sometimes be difficult Authors tried to capture repeatable

techniques for performance tuning

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Why Tune RMAN

Backups taking too long Performance of the system is impacted

during RMAN backups Restore and recovery time too long,

downtime causes the business to lose money

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One Approach to Tuning...

1. Identify measurable business performance requirements.

2. Collect data and measure performance.3. Identify bottlenecks.4. Make adjustments that will alleviate the

worst bottleneck.5. Repeat steps 1–4 until your performance

goals are achieved.

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Systemic Influences

CPU Memory Operating system Disk layout Network Database architecture Tape technology and vendor Application design Design of data model and its physical implementation Robustness of SQL statements

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Views Used for Monitoring

V$RMAN_BACKUP_JOB_DETAILS V$BACKUP_ASYNC_IO V$BACKUP_SYNC_IO V$PROCESS V$SESSION V$SESSION_LONGOPS V$RECOVERY_PROGRESS V$SESSION_WAIT

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Identifying RMAN Processes

Sometimes you might want to kill an RMAN process

SQL> SELECT b.sid, b.serial#, a.spid, b.client_info

FROM v$process a, v$session bWHERE a.addr = b.paddrAND b.client_info LIKE '%rman%';

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Measuring Backup Performance

If you can’t measure it, you can’t manage it...

SQL> SELECT session_recid, input_bytes_per_sec_display,

output_bytes_per_sec_display, time_taken_display, end_time FROM v$rman_backup_job_details ORDER BY end_time;

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Monitoring RMAN Job Progress

Are we there yet? Are we there yet?

SQL> select sid, serial#, sofar, totalwork, opname, round(sofar/totalwork*100,2) "% Complete" from v$session_longops where opname LIKE 'RMAN%' and opname NOT LIKE '%aggregate%' and totalwork != 0 and sofar <> totalwork;

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Identifying I/O Bottlenecks

How do you determine I/O is a bottleneck? Asynchronous I/O vs. synchronous

SQL> SELECT sid, serial, filename, type, elapsed_time, effective_bytes_per_second

FROM v$backup_async_io

WHERE close_time > sysdate – 7;

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Improving Tape I/O Performance

RMAN can be configured to backup directly to tape (see MML chapter)

Tape I/O is often the bottleneck Can be difficult to diagnose and resolve Use an incremental backup strategy with

block change tracking Adjust multiplexing of backup sets

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Improving Tape I/O Performance

Many variables to consider... MML software configuration Network configuration Level of tape compression Tape streaming Tape block size

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Maximizing Throughput to Backup Device

Multiplexing with RMAN means it can read multiple files at the same time and simultaneously write them to the same backup piece

As of Oracle 10g, RMAN will automatically tune the level of multiplexing

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Maximizing Throughput to Backup Device

Filesperset limits the number of files in each backup set

Maxopenfiles limits the number of files simultaneously open

Diskratio instructs RMAN to read datafiles from a specified number of disks

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Setting Large Pool Memory Size

One approach, use ASMM

1. Ensure statistics_level is set to TYPICAL (the default) or ALL2. Set sga_target to an appropriate nonzero value for your

database not exceeding the sga_max_size3. Set the following initialization parameters to zero:

– shared_pool_size– large_pool_size– java_pool_size– db_cache_size– streams_pool_size

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Tuning Media Recovery

With Oracle 10g or higher, RMAN should automatically perform recovery in parallel

You can override the default behavior:

RMAN> recover database parallel 4;

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Tuning Crash Recovery

Crash recovery is performed by SMON after a database crash (power outage, shutdown abort)

Why would you care how long crash recovery takes?

Can be tuned with fast_start_mttr_target Gives the database a target time for

performing crash recovery

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One Approach to Tuning Crash Recovery

1. Disable the initialization parameters that interfere with fast_start_mttr_target

2. Determine the lower bound for fast_start_mttr_target

3. Determine the upper bound for fast_start_mttr_target

4. Select a value within the upper and lower bounds

5. Monitor and adjust

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Slowing RMAN Down

Sometimes RMAN can impact other processes running on the system

Couple of techniques:– The backup duration ... minimize load command– The rate clause of the allocate channel or

configure channel command

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Improving Performance Through Parallelism

Use the parallel clause of the configure command

Doesn’t do much for single disk systems

RMAN> configure device type

disk parallelism 4;

RMAN> show channel;

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Improving Performance Using Incremental Features

RMAN has many incremental features Incremental backups Change tracking Incremental update