1 Chapter 16 Tuning RMAN

2 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

3 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

4 One Approach to Tuning 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.

5 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

6 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

7 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 b WHERE a.addr = b.paddr AND b.client_info LIKE '%rman%';

8 Measuring Backup Performance If you cant measure it, you cant 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;

9 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;

10 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;

11 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

12 Improving Tape I/O Performance Many variables to consider... MML software configuration Network configuration Level of tape compression Tape streaming Tape block size

13 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

14 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

15 Setting Large Pool Memory Size One approach, use ASMM 1. Ensure statistics_level is set to TYPICAL (the default) or ALL 2. Set sga_target to an appropriate nonzero value for your database not exceeding the sga_max_size 3. Set the following initialization parameters to zero: – shared_pool_size – large_pool_size – java_pool_size – db_cache_size – streams_pool_size

16 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;

17 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

18 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

19 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

20 Improving Performance Through Parallelism Use the parallel clause of the configure command Doesnt do much for single disk systems RMAN> configure device type disk parallelism 4; RMAN> show channel;

21 Improving Performance Using Incremental Features RMAN has many incremental features Incremental backups Change tracking Incremental update