TUNING RMAN PART – I



In this post and the next one, I will discuss various methods by which we can improve the
performance of RMAN backup and recovery.
RMAN backup/recovery performance is influenced by various parameters:
– Parallelism
– Maxpiecesize – Maximum size of each backup piece
– FIlesperset  _ The number of datafiles in each backupset
– Maxopenfiles – Maximum No. of files which can be read from simultaneously
– Multiplexing level
– Asynchronous / Synchronous I/O
– Large pool Size-
- SETUP
As part of setup I will create 4 more tablespaces . I already have 5 tablespaces in my
database. So in all I will have 9 tablespaces .
sql>conn / as sysdba
create tablespace rman1
datafile ‘C:\APP\ADMINISTRATOR\ORADATA\ORCL\rman1.dbf’ size 100m;
create tablespace rman2
datafile ‘C:\APP\ADMINISTRATOR\ORADATA\ORCL\rman2.dbf’ size 100m;
create tablespace rman3
datafile ‘C:\APP\ADMINISTRATOR\ORADATA\ORCL\rman3.dbf’ size 100m;
create tablespace rman4
datafile ‘C:\APP\ADMINISTRATOR\ORADATA\ORCL\rman4.dbf’ size 100m;
create table hr.test1 tablespace rman1 as select * from hr.employees;
create table hr.test2 tablespace rman2 as select * from hr.employees;
create table hr.test3 tablespace rman3 as select * from hr.employees;
create table hr.test4 tablespace rman4 as select * from hr.employees;
Let us discuss each parameters one by one .
– PARALLELISM –

we can parallelize the backup/recovery operation by

– setting parallelism for the device
– Allocating multiple channels and

  • . Let RMAN decide which file to backup/restore using which channel
  • . BAcking up/Restoring specified files using specified channel

Each channel used will create its own backupset.

-- SET PARALLELSM FOR DEVICE –

RMAN>delete backup;
configure device type disk parallelism 3;
backup format ‘c:\%U.bak’ tablespace rman1, rman2, rman3;
list backup of tablespace rman1, rman2, rman3;
List of Datafiles in backup set 25

6       Full 1583594    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN1.DBF

List of Datafiles in backup set 26

7       Full 1583595    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DBF

List of Datafiles in backup set 27

8       Full 1583596    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DBF
——————————————————————————————-
- Allocating multiple channels and let RMAN decide which file to backup using which channel
———————————————————————————————-
— Note that RMan decides to backup rman1 and rman3 using c1 and rman2 using c2
RMAN>configure device type disk parallelism 1;
delete backup;
RMAN>run{
allocate channel c1 device type disk format ‘c:\%U.bak';
allocate channel c2 device type disk format ‘c:\%U.bak';
backup tablespace rman1, rman2, rman3;
}

channel c1: specifying datafile(s) in backup set
input datafile file number=00006 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN1.DBF
input datafile file number=00008 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DBF
channel c2: specifying datafile(s) in backup set
input datafile file number=00007 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DBF
-- Check that each channel created its own backupset

RMAN>list backup;
List of Datafiles in backup set 28
6       Full 1584178    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN1.DBF
8       Full 1584178    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DBF

List of Datafiles in backup set 29
7       Full 1584179    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DBF
————————————————————————————–
- Allocating multiple channels and backing up specified files using specified channels
————————————————————————————–
— Note that RMan  backs up rman1 and rman2 using c1 and rman3 using c2 as specified
RMAN>delete backup;
run{
allocate channel c1 device type disk format ‘c:\%U.bak';
allocate channel c2 device type disk format ‘c:\%U.bak';
backup (tablespace rman1, rman2 channel c1)
(tablespace rman3 channel c2);
}

channel c1: specifying datafile(s) in backup set
input datafile file number=00006 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN1.DB
input datafile file number=00007 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DB

channel c2: specifying datafile(s) in backup set
input datafile file number=00008 name=C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DB

– Check that each channel created its pwn backupset
RMAN>list backup;
List of Datafiles in backup set 30
6       Full 1584550    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN1.DBF
7       Full 1584550    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DBF
List of Datafiles in backup set 31
8       Full 1584551    12-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DBF
———————
-— FILESPERSET –
-———————
– This parameter decides how many files will be included in one backupset.
If > 1 files are backed up and filesperset = 1, one backupset will be created for each file

rman>delete backup;
rman>backup datafile 7,8 filesperset 1 format ‘c:\%U.bak';

list backup ;
— Note that two backupsets are created with one datafile each
List of Backup Sets
===================
List of Datafiles in backup set 17

7       Full 1529096    11-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN2.DBF
List of Datafiles in backup set 18

8       Full 1529098    11-SEP-12 C:\APP\ADMINISTRATOR\ORADATA\ORCL\RMAN3.DBF

Using this parameter we can reduce the recovery time by limiting the no. of files per
backupset, since to restore a particular datafile we will have to restore a smaller file.
This is also beneficial in case the backup fails in the middle. Next time, we can backup
only those datafiles which could not be successfully backed up.
————————–
— MAXPIECESIZE –
————————–
– This parameter controls the maximum size a backup piece can have
– If we backup only one file, it will split into multiple pieces

- Check the size of datafiles.
– Note that datafile datafile for tablespace sysaux is 570m in size

rman>report schema;
File Size(MB) Tablespace           RB segs Datafile Name
—- ——– ——————– ——- ————————
1    690      SYSTEM               ***     C:\APP\ADMINISTRATOR\ORADATA\ORCL\SYSTEM01.DBF
2    570      SYSAUX               ***     C:\APP\ADMINISTRATOR\ORADATA\ORCL\SYSAUX01.DBF

– Backup datafile for sysaux tablespace so that each piece size <= 200M
— Note that backup is spread over 3 backup pieces

rman>delete backup;
rman>run{
allocate channel c1 device type disk maxpiecesize 200m format ‘c:\%U.bak';
backup tablespace sysaux ;
}
list backup of tablespace sysaux;
List of Backup Pieces for backup set 21 Copy #1
BP Key  Pc# Status      Piece Name
——- — ———– ———-
21      1   AVAILABLE   C:\0NNKUKP0_1_1.BAK
22      2   AVAILABLE   C:\0NNKUKP0_2_1.BAK
23      3   AVAILABLE   C:\0NNKUKP0_3_1.BAK

This option can be used
– to exercise the operating system limit on the file size.
– to split the backup of a datafile into multiple pieces if the backup does not fit in one
tape
– if backup is to be transferred over network.
————————–
— MAXOPENFILES -
————————-
— This parameter decides how many files can be backed up simultaneously
i.e. data from how many files can be read at a time.
— Default value = 8

– Take backup of 2 datafiles with maxopenfiles = 1 so that  level of multiplexing = 1 i.e.
. datafile 1 will be backed up first
. datafile 2 will be backed up next
so that data from 2 files will not be intermingled.
Rather first all data from datafile 1 will be written and
then data from datafile 2 will be written.

– While the backup is still going on issue the next sql query
RMAN> run{
allocate channel c1 device type disk maxopenfiles 1;
backup datafile 1,2;
}

— Note the change in filename from system01.dbf to sysaux01.dbf
— Note that buffers are allocated to datafile 1 first,
when that has been backed up, then buffers are allocated
to datafile 2
— Since multiplexing level = 1, total of 16 buffers of 1M each are
all allocated to each file one by one

sql>col filename for a25 word_wrapped
select type, status, filename, buffer_size, buffer_count
from v$backup_async_io
where type <> ‘AGGREGATE’
and status = ‘IN PROGRESS';
TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD     1048576           16
ATA\ORCL\SYSTEM01.DBF
OUTPUT    IN PROGRESS C:\APP\ADMINISTRATOR\FLAS     1048576            4
H_RECOVERY_AREA\ORCL\BACK
UPSET\2012_09_11\O1_MF_NN
NDF_TAG20120911T152958_84
Y2WZ7B_.BKP

SQL> /
TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD     1048576           16
ATA\ORCL\SYSAUX01.DBF
OUTPUT    IN PROGRESS C:\APP\ADMINISTRATOR\FLAS     1048576            4
H_RECOVERY_AREA\ORCL\BACK
UPSET\2012_09_11\O1_MF_NN
NDF_TAG20120911T152958_84
Y2WZ7B_.BKP

– Take backup of 2 datafiles with maxopenfiles = 2 so that  level of multiplexing = 2 i.e.
. datafile 1 and 2  will be backed up simultaneously so that data from 2 files will be intermingled.

– While the backup is still going on issue the next sql query
RMAN> run{
allocate channel c1 device type disk maxopenfiles 2;
backup datafile 1,2;
}

— Note that buffers are allocated simultaneously to datafile 1 and 2
— Since multiplexing level = 2 (< 4), total of 16 buffers of 1M each are  allocated.
Each file gets 8 buffers each of the size of 1M

sql>col filename for a25 word_wrapped
select type, status, filename, buffer_size, buffer_count
from v$backup_async_io
where type <> ‘AGGREGATE’
and status = ‘IN PROGRESS';

TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD    1048576            8
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD     1048576            8
ATA\ORCL\SYSAUX01.DBF
OUTPUT    IN PROGRESS C:\APP\ADMINISTRATOR\FLAS     1048576            4
H_RECOVERY_AREA\ORCL\BACK
UPSET\2012_09_11\O1_MF_NN
NDF_TAG20120911T153330_84
Y33M40_.BKP
——————–
— MULTIPLEXING
——————–
Level of multiplexing means the no. of files whose data is intermingled
in the backup file. It depends on the following:
– # of files being backed up using one channel
– FIlesperset
– Maxopenfiles
Level of multiplexing = Minimum of the above 3.
We increase level of multiplexing so that data can be simultaneously read from multiple
files so that even if a process to wait to read from one of the files being backed up due to
contention, it can still read from the other files so that output tape drives gets
continuous input. Otherwise, due to  lack of the input data, tape drive might overshoot
before stopping and will again have to come back to its earlier position when it gets next
stream of data.
Thus, increasing the level of multiplexing may increase the speed of backup. On the other
hand , it can reduce the restore speed as data for a file has to be extracted from the
intermingled data.
Thus , one has to decide the level of multiplexing based on whether performance of the
backup or recovery is more critial.
In case files being backed up are ASM files, level of multiplexing may be reduced as ASM
automatically takes care of the contention by striping the data.
Input buffers are allocated for the backup. The no. of buffers allocated per file depends
upon the level of multiplexing.
Multiplexing level        Allocation rule

Level <= 4           1 MB buffers are allocated so that the total buffer size for all
input files is 16 MB.
4 < Level <= 8       512 KB are allocated so that the total buffer size for all files is
less than 16 MB.
Level > 8            RMAN allocates four 128 KB disk buffers per channel for each file,
so that the total size is 512 KB per channel for each file.

For multiplexing level 1 and 2 we have already seen that 1 MB buffers are allocated so that
the total buffer size for all input files is 16 MB.
—————————————–
Let’s verify for multiplexing level of 5 .
—————————————–

RMAN>delete backup;
=- Note that 512 KB are allocated so that the total buffer size for all files is less than
16 MB.
— AS backup progresses the files which have been backed up, buffers allocated to them gets
freed
RMAN> run{
allocate channel c1 device type disk maxopenfiles 5;
backup datafile 1,2,3,4,5;
}

sql>/
TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSAUX01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\UNDOTBS01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\EXAMPLE01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\USERS01.DBF

sql>/

TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSAUX01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\UNDOTBS01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\EXAMPLE01.DBF
sql>/

TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD     524288            6
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSAUX01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\EXAMPLE01.DBF
sql>/

INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSAUX01.DBF
sql>/

TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      524288            6
ATA\ORCL\SYSTEM01.DBF

—————————————–
Let’s verify for multiplexing level of 9 (> 8) .
—————————————–

RMAN>delete backup;
RMAN> run{
allocate channel c1 device type disk maxopenfiles 9;
backup datafile 1,2,3,4,5,6,7,8,9;
}
— Note that buffers are allocated simultaneously to all the 9 datafiles so that data from all the files will be intermingled in the output file.
— Since multiplexing level = 9 ( Level > 8), RMAN allocates four 128 KB disk buffers per channel for each file, so that the total size is 512 KB per channel for each file.

sql>col filename for a25 word_wrapped
select type, status, filename, buffer_size, buffer_count
from v$backup_async_io
where type <> ‘AGGREGATE’
and status = ‘IN PROGRESS';
TYPE      STATUS      FILENAME                  BUFFER_SIZE BUFFER_COUNT
——— ———– ————————- ———– ————
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD     131072            4
ATA\ORCL\SYSTEM01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\SYSAUX01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\UNDOTBS01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\EXAMPLE01.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\RMAN1.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\RMAN2.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\RMAN3.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\RMAN4.DBF
INPUT     IN PROGRESS C:\APP\ADMINISTRATOR\ORAD      131072            4
ATA\ORCL\USERS01.DBF
Conclusion :

- We can parallelize the backup/recovery operation by
   – setting parallelism for the device
   – Allocating multiple channels and
      . Let RMAN decide which file to backup/restore using which channel
      . BAcking up/Restoring specified files using specified channels
- Filesperset
  . Using this parameter we can reduce the recovery time by limiting the no. of files per
backupset, since to restore a particular datafile we will have to restore a smaller file.
  . This is also beneficial in case the backup fails in the middle. Next time, we can backup
only those datafiles which could not be successfully backed up.
- Maxpiecesize
  This option can be used
   – to exercise the operating system limit on the file size.
   – to split the backup of a datafile into multiple pieces if the backup does not fit in one tape
   – if backup is to be transferred over network.
- Maxopenfiles
  This parameter decides how many files can be backed up simultaneously i.e. data from how many files can be read at a time.
- Multiplexing
  Level of multiplexing means the no. of files whose data is intermingled in the backup file. It depends on the following:
- # of files being backed up using one channel
- FIlesperset
- Maxopenfiles
Level of multiplexing = Minimum of the above 3.
   – Increasing the level of multiplexing can effectively keep the tape streaming.
   – Increasing the level of multiplexing may increase the speed of backup. On the other
hand , it can reduce the restore speed as data for a file has to be extracted from the
intermingled data.
   – Thus , one has to decide the level of multiplexing based on whether performance of the
backup or recovery is more critial.
   – In case files being backed up are ASM files, level of multiplexing may be reduced as ASM automatically takes care of the contention by striping the data.
- Input buffers are allocated for the backup. The no. of buffers allocated per file depends
upon the level of multiplexing.
Multiplexing level        Allocation rule
   Level <= 4           1 MB buffers are allocated so that the total buffer size for all
input files is 16 MB.
   4 < Level <= 8       512 KB are allocated so that the total buffer size for all files is
less than 16 MB.
   Level > 8            RMAN allocates four 128 KB disk buffers per channel for each file,
so that the total size is 512 KB per channel for each file.
- We can calculate the size of the buffers required by RMAN as follows:
    Multiply the total buffer bytes for each data file by the number of data files that are being concurrently accessed by the channel, and then multiply this number by the number of channels.
Assume that you use one channel to back up four data files, and use the settings that are shown above. In this case, multiply as follows to obtain the total size of the buffers that are allocated for the backup:
4 MB per data file Î 1 channel Î 4 data files per channel = 16 MB
In my next post
Tuning RMAN Part-II ,I will discuss the use of the asynchronous i/o to improve the performance of RMAN backup/recovery.

Thanx for your time. Happy Tuning !!

References

http://docs.oracle.com/cd/B28359_01/backup.111/b28270/rcmcncpt.htm#BRADV89486
http://hemantoracledba.blogspot.in/2015/07/rman-5-useful-keywords-and-subclauses.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed:+blogspot/JcnHK+(Hemant%27s+Oracle+DBA+Blog)
http://hemantoracledba.blogspot.in/2015/07/rman-5b-more-useful-keywords-and.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed:+blogspot/JcnHK+(Hemant%27s+Oracle+DBA+Blog)
http://hemantoracledba.blogspot.in/2015/07/rman-5c-some-more-useful-keywords-and.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed:+blogspot/JcnHK+(Hemant%27s+Oracle+DBA+Blog)
Retention Policy and Control_file_record_keep_time
3 RMAN Parameters every DBA should know
Spreading RMAN Backups Across Multiple Disks
Triplexing RMAN Backups

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6 thoughts on “TUNING RMAN PART – I

  1. Hi Anju Nice Information as always,
    Can you describe how to configure multiple channels while restore operations or setting parallelism will automatically take care of it.
    In short How to improve performance during restore

    1. Hi Fahim,

      Thanks for your time and feedback.
      In case of restore also, multiple channels can be configured by
      – setting parallelism or
      – allocating multiple channels within run block.

      Hope it helps!
      Your comments and suggestions are always welcome.

      regards
      Anju

  2. RMAN>run{
    allocate channel c1 device type disk format ‘c:\%U.bak';
    allocate channel c2 device type disk format ‘c:\%U.bak';
    backup tablespace rman1, rman2, rman3;
    }

    each channel created its own backupset.

    why here we are getting no of bkpsets=no of channels?
    generally the no of times we use backup keyword in rman run block, we get equal no of backup sets. and no of bkp piece = no of channels
    how we can determine no of bkp set and bkp piece?

    1. No. of backupsets created = Degree of parallelism

      No. of backup pieces is decided by maxpiecesize parameter. If size of backupset exceeds MAXPIECESIZE, a backupset can contain multiple backup pieces each having size <= MAXPIECESIZE. Additionally, a multisection backupset can also contain multiple backup pieces in a backupset.

  3. Hi Anju,
    a great blog post on RMAN !

    I’m trying to optimize +5TB b/u on a 2 node RAC db.
    14 datafiles, where one datafile is 2,6 TB (BLOBS), six datafiles between 300-800 MB and the rest (7) < 30MB
    Currently the config is 3+3 channels and 1 filesperset

    This setup ends up with one big datafile running on one channel during the whole execution time.

    How to best parallelize to enable split of large datafiles ?
    Section size ?

    Thx,
    reg peter

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