手工指定CHANNEL與設定PARALLELISM引數的異同以及FILESPERSET引數的作用

bfc99發表於2014-01-25
Parallel
下面以實驗的方式，展示在RUN塊中手工指定多通道（CHANNEL，也有稱之為“通道”） 與設定並行度PARALLELISM引數 的異同，以及FILESPERSET引數的作用。

RMAN備份時，為了加快備份的速度，提供了並行處理的方式。一種是設定多個通道，另一種是設定PARALLELISM引數。那麼這兩種方式有什麼不同呢？今天在實驗的方式來加深理解。

首先，我們來實驗第一種方式，即設定多個通道的方式。為了比較增加通道後的效果，我們先做一次單通道的備份操作。

[oracle@localhost ~]$ rman target /
Recovery Manager: Release 10.2.0.5.0 - Production on Sat Jan 25 15:22:13 2014
Copyright (c) 1982, 2007, Oracle. All rights reserved.
connected to target database: ORCL (DBID=1347935162)
RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
}2> 3> 4> 5>
using target database control file instead of recovery catalog
allocated channel: c1
channel c1: sid=158 devtype=DISK
Starting backup at 20140125 15:27:37
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c1: starting piece 1 at 20140125 15:27:38
channel c1: finished piece 1 at 20140125 15:28:23
piece handle=/oradata/orcl/databak1/8iouvaba_1_1 tag=TAG20140125T152737 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:45
Finished backup at 20140125 15:28:23
Starting Control File and SPFILE Autobackup at 20140125 15:28:23
piece handle=/oradata/orcl/databak/c-1347935162-20140125-08 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 15:28:26
released channel: c1

可見，資料庫的備份時間約為49秒（15:27:37至15:28:26）。

下面我們設定2個通道，來執行備份。

RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c2 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
release channel c2;
}2> 3> 4> 5> 6> 7>
allocated channel: c1
channel c1: sid=158 devtype=DISK
allocated channel: c2
channel c2: sid=147 devtype=DISK
Starting backup at 20140125 15:31:45
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
channel c1: starting piece 1 at 20140125 15:31:45
channel c2: starting full datafile backupset
channel c2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel c2: starting piece 1 at 20140125 15:31:45
channel c2: finished piece 1 at 20140125 15:32:00
piece handle=/oradata/orcl/databak1/8louvaj1_1_1 tag=TAG20140125T153145 comment=NONE
channel c2: backup set complete, elapsed time: 00:00:15
channel c1: finished piece 1 at 20140125 15:32:35
piece handle=/oradata/orcl/databak1/8kouvaj1_1_1 tag=TAG20140125T153145 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:50
Finished backup at 20140125 15:32:35
Starting Control File and SPFILE Autobackup at 20140125 15:32:35
piece handle=/oradata/orcl/databak/c-1347935162-20140125-09 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 15:32:38
released channel: c1
released channel: c2

2個通道的情況下，備份時間約為53秒（15:31:45至15:32:38）。時間上還要慢了一些。
而且，我們發現，組成資料庫的資料檔案一共有6個，當用2個通道備份時，其自動分成了兩組，每組3個檔案。
備份結束後，每個通道生成一個備份檔案，共兩個備份檔案。
我們再試試3個通道時的情況
RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c2 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c3 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
release channel c2;
release channel c3;
}2> 3> 4> 5> 6> 7> 8> 9>
allocated channel: c1
channel c1: sid=158 devtype=DISK
allocated channel: c2
channel c2: sid=147 devtype=DISK
allocated channel: c3
channel c3: sid=138 devtype=DISK
Starting backup at 20140125 15:39:06
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c1: starting piece 1 at 20140125 15:39:07
channel c2: starting full datafile backupset
channel c2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel c2: starting piece 1 at 20140125 15:39:07
channel c3: starting full datafile backupset
channel c3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel c3: starting piece 1 at 20140125 15:39:07
channel c2: finished piece 1 at 20140125 15:39:14
piece handle=/oradata/orcl/databak1/8oouvb0r_1_1 tag=TAG20140125T153906 comment=NONE
channel c2: backup set complete, elapsed time: 00:00:07
channel c1: finished piece 1 at 20140125 15:39:59
piece handle=/oradata/orcl/databak1/8nouvb0r_1_1 tag=TAG20140125T153906 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:52
channel c3: finished piece 1 at 20140125 15:39:59
piece handle=/oradata/orcl/databak1/8pouvb0r_1_1 tag=TAG20140125T153906 comment=NONE
channel c3: backup set complete, elapsed time: 00:00:52
Finished backup at 20140125 15:39:59
Starting Control File and SPFILE Autobackup at 20140125 15:39:59
piece handle=/oradata/orcl/databak/c-1347935162-20140125-0a comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 15:40:02
released channel: c1
released channel: c2
released channel: c3
3個通道的情況下，備份時間約為56秒（15:39:06至15:40:02）
而且，6個資料檔案也被分成了三組，每組2個檔案。那麼如果我設成4個通道，6個檔案會如何分組呢？
RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c2 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c3 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c4 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
release channel c2;
release channel c3;
release channel c4;
}
2> 3> 4> 5> 6> 7> 8> 9> 10> 11>
allocated channel: c1
channel c1: sid=158 devtype=DISK
allocated channel: c2
channel c2: sid=147 devtype=DISK
allocated channel: c3
channel c3: sid=138 devtype=DISK
allocated channel: c4
channel c4: sid=137 devtype=DISK
Starting backup at 20140125 15:42:49
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c1: starting piece 1 at 20140125 15:42:49
channel c2: starting full datafile backupset
channel c2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel c2: starting piece 1 at 20140125 15:42:49
channel c3: starting full datafile backupset
channel c3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel c3: starting piece 1 at 20140125 15:42:49
channel c2: finished piece 1 at 20140125 15:43:04
piece handle=/oradata/orcl/databak1/8souvb7p_1_1 tag=TAG20140125T154249 comment=NONE
channel c2: backup set complete, elapsed time: 00:00:15
channel c3: finished piece 1 at 20140125 15:43:39
piece handle=/oradata/orcl/databak1/8touvb7p_1_1 tag=TAG20140125T154249 comment=NONE
channel c3: backup set complete, elapsed time: 00:00:50
channel c1: finished piece 1 at 20140125 15:43:46
piece handle=/oradata/orcl/databak1/8rouvb7p_1_1 tag=TAG20140125T154249 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:57
Finished backup at 20140125 15:43:46
Starting Control File and SPFILE Autobackup at 20140125 15:43:46
piece handle=/oradata/orcl/databak/c-1347935162-20140125-0b comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 15:43:47
released channel: c1
released channel: c2
released channel: c3
released channel: c4
分配了4個通道，但備份過程中，只實際使用了3個。備份的時間為58秒（15:42:49至15:43:47 ）。
到了這裡，看來RMAN是在各個通道間平均分配檔案數量的。推測一下，如果設成6個通道，應該就是一個檔案一個通道了。
RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c2 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c3 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c4 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c5 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c6 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
release channel c2;
release channel c3;
release channel c4;
release channel c5;
release channel c6;
}2> 3> 4> 5> 6> 7> 8> 9> 10> 11> 12> 13> 14> 15> 16>
allocated channel: c1
channel c1: sid=158 devtype=DISK
allocated channel: c2
channel c2: sid=147 devtype=DISK
allocated channel: c3
channel c3: sid=138 devtype=DISK
allocated channel: c4
channel c4: sid=137 devtype=DISK
allocated channel: c5
channel c5: sid=156 devtype=DISK
allocated channel: c6
channel c6: sid=155 devtype=DISK
Starting backup at 20140125 15:57:58
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
channel c1: starting piece 1 at 20140125 15:57:58
channel c2: starting full datafile backupset
channel c2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
channel c2: starting piece 1 at 20140125 15:57:58
channel c3: starting full datafile backupset
channel c3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
channel c3: starting piece 1 at 20140125 15:57:58
channel c4: starting full datafile backupset
channel c4: specifying datafile(s) in backupset
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel c4: starting piece 1 at 20140125 15:57:58
channel c5: starting full datafile backupset
channel c5: specifying datafile(s) in backupset
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel c5: starting piece 1 at 20140125 15:57:58
channel c6: starting full datafile backupset
channel c6: specifying datafile(s) in backupset
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c6: starting piece 1 at 20140125 15:57:58
channel c5: finished piece 1 at 20140125 15:58:01
piece handle=/oradata/orcl/databak1/93ouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c5: backup set complete, elapsed time: 00:00:03
channel c2: finished piece 1 at 20140125 15:58:08
piece handle=/oradata/orcl/databak1/90ouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c2: backup set complete, elapsed time: 00:00:10
channel c6: finished piece 1 at 20140125 15:58:08
piece handle=/oradata/orcl/databak1/94ouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c6: backup set complete, elapsed time: 00:00:10
channel c4: finished piece 1 at 20140125 15:58:11
piece handle=/oradata/orcl/databak1/92ouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c4: backup set complete, elapsed time: 00:00:13
channel c3: finished piece 1 at 20140125 15:58:36
piece handle=/oradata/orcl/databak1/91ouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c3: backup set complete, elapsed time: 00:00:39
channel c1: finished piece 1 at 20140125 15:58:52
piece handle=/oradata/orcl/databak1/8vouvc46_1_1 tag=TAG20140125T155758 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:54
Finished backup at 20140125 15:58:52
Starting Control File and SPFILE Autobackup at 20140125 15:58:52
piece handle=/oradata/orcl/databak/c-1347935162-20140125-0c comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 15:58:55
released channel: c1
released channel: c2
released channel: c3
released channel: c4
released channel: c5
released channel: c6
果然，如推測中的一樣。是一個通道一個檔案，最終生成了6個備份檔案。總用時約57秒（15:57:58至 15:58:55）
經過以上實驗，得出以下結論：
1、增加通道，RMAN會並行處理備份任務，但根據硬體環境的不同，並不是越多越快。以本次實驗來說，備份時間最省的，卻是隻有一個通道的時候。這可能是因為實驗環境為一跑在普通桌上型電腦上的虛擬機器所致，其本身的並行處理能力就低。
2、當設有多個通道時，資料檔案會平均分配至各個通道上。若檔案不能全部均分至所有通道上，則會放棄部分通道的使用。例如上面實驗中的6個資料檔案在4個通道上備份時，則實際上只使用了3個通道。可是，假如組成資料庫的資料檔案的個數是質數（只能被它自己和1整除的數），比如7個檔案。當設定為4個通道時，會如何分配呢？由於無論是用4個，還是3個或2個通道，我們都不能把資料檔案均分到通道上。這裡先賣個關子，為了保證我們下面的實驗可以在相同的環境下完成，這個實驗，我們放到最後。
3、自動備份的控制檔案和引數檔案並沒有備份到通道指定的位置（/oradata/orcl/databak1），而放存放到了RMAN中配置的“控制檔案自動備份”所指定的位置（見下面紅字部分）。
RMAN> show all;
RMAN configuration parameters are:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
CONFIGURE BACKUP OPTIMIZATION OFF;
CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/oradata/orcl/databak/%F';
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT '/oradata/orcl/databak/%U';
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/oracle/app/oracle/product/10.2/db_1/dbs/snapcf_orcl.f'; # default
現在再來看並行度PARALLELISM這個引數。這個引數要通過輸入以下命令來設定（這裡設定的並行度為3）：
RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters are successfully stored
我們再執行一個通道的備份，看看是什麼效果。
RMAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
}2> 3> 4> 5>
allocated channel: c1
channel c1: sid=158 devtype=DISK
Starting backup at 20140125 16:20:32
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c1: starting piece 1 at 20140125 16:20:32
channel c1: finished piece 1 at 20140125 16:21:17
piece handle=/oradata/orcl/databak1/9bouvdeg_1_1 tag=TAG20140125T162032 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:45
Finished backup at 20140125 16:21:17
Starting Control File and SPFILE Autobackup at 20140125 16:21:17
piece handle=/oradata/orcl/databak/c-1347935162-20140125-0f comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 16:21:18
released channel: c1
嘿嘿，在RUN塊中指定通道時，這個引數是不管用的。也就是說，你在RUN塊內指定了幾個通道，就用幾個通道去備份，與這個PARALLELISM這個引數無關。
那我們直接在RMAN中輸入BACKUP DATABASE；會是什麼效果呢？
RMAN> backup database;
Starting backup at 20140125 16:24:41
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=158 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=147 devtype=DISK
allocated channel: ORA_DISK_3
channel ORA_DISK_3: sid=138 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 16:24:42
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 16:24:42
channel ORA_DISK_3: starting full datafile backupset
channel ORA_DISK_3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel ORA_DISK_3: starting piece 1 at 20140125 16:24:42
channel ORA_DISK_2: finished piece 1 at 20140125 16:24:49
piece handle=/oradata/orcl/databak/9eouvdma_1_1 tag=TAG20140125T162441 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:07
channel ORA_DISK_1: finished piece 1 at 20140125 16:25:24
piece handle=/oradata/orcl/databak/9douvdma_1_1 tag=TAG20140125T162441 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:42
channel ORA_DISK_3: finished piece 1 at 20140125 16:25:24
piece handle=/oradata/orcl/databak/9fouvdma_1_1 tag=TAG20140125T162441 comment=NONE
channel ORA_DISK_3: backup set complete, elapsed time: 00:00:42
Finished backup at 20140125 16:25:24
Starting Control File and SPFILE Autobackup at 20140125 16:25:24
piece handle=/oradata/orcl/databak/c-1347935162-20140125-10 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 16:25:27
RMAN自動建立了三個通道，ORA_DISK_1至3。備份時間為46秒（16:24:41至16:25:27）。這個時間要比我們手工指定三個通道（56秒）時快。
再設定並行度為4看看效果。
RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 4 BACKUP TYPE TO BACKUPSET;
old RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 4 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters are successfully stored
released channel: ORA_DISK_1
released channel: ORA_DISK_2
released channel: ORA_DISK_3
RMAN> backup database;
Starting backup at 20140125 16:26:38
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=158 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=147 devtype=DISK
allocated channel: ORA_DISK_3
channel ORA_DISK_3: sid=138 devtype=DISK
allocated channel: ORA_DISK_4
channel ORA_DISK_4: sid=137 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 16:26:38
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 16:26:38
channel ORA_DISK_3: starting full datafile backupset
channel ORA_DISK_3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel ORA_DISK_3: starting piece 1 at 20140125 16:26:39
channel ORA_DISK_2: finished piece 1 at 20140125 16:26:54
piece handle=/oradata/orcl/databak/9iouvdpu_1_1 tag=TAG20140125T162638 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:16
channel ORA_DISK_1: finished piece 1 at 20140125 16:27:29
piece handle=/oradata/orcl/databak/9houvdpu_1_1 tag=TAG20140125T162638 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:51
channel ORA_DISK_3: finished piece 1 at 20140125 16:27:29
piece handle=/oradata/orcl/databak/9jouvdpu_1_1 tag=TAG20140125T162638 comment=NONE
channel ORA_DISK_3: backup set complete, elapsed time: 00:00:51
Finished backup at 20140125 16:27:29
Starting Control File and SPFILE Autobackup at 20140125 16:27:29
piece handle=/oradata/orcl/databak/c-1347935162-20140125-11 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 16:27:32
和我們手工指定4個通道時類似，備份時只實際使用了3個通道。備份的時間為54秒（16:26:38至16:27:32），和上面手工指定4個通道所用時間來比，稍快一點兒。但比剛才自動3通道的要慢。
再設定並行度為7看看效果。
RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 7 BACKUP TYPE TO BACKUPSET;
old RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 4 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 7 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters are successfully stored
released channel: ORA_DISK_1
released channel: ORA_DISK_2
released channel: ORA_DISK_3
released channel: ORA_DISK_4
RMAN> backup database;
Starting backup at 20140125 16:29:00
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=158 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=147 devtype=DISK
allocated channel: ORA_DISK_3
channel ORA_DISK_3: sid=138 devtype=DISK
allocated channel: ORA_DISK_4
channel ORA_DISK_4: sid=137 devtype=DISK
allocated channel: ORA_DISK_5
channel ORA_DISK_5: sid=156 devtype=DISK
allocated channel: ORA_DISK_6
channel ORA_DISK_6: sid=155 devtype=DISK
allocated channel: ORA_DISK_7
channel ORA_DISK_7: sid=134 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_3: starting full datafile backupset
channel ORA_DISK_3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
channel ORA_DISK_3: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_4: starting full datafile backupset
channel ORA_DISK_4: specifying datafile(s) in backupset
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel ORA_DISK_4: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_5: starting full datafile backupset
channel ORA_DISK_5: specifying datafile(s) in backupset
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel ORA_DISK_5: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_6: starting full datafile backupset
channel ORA_DISK_6: specifying datafile(s) in backupset
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel ORA_DISK_6: starting piece 1 at 20140125 16:29:02
channel ORA_DISK_6: finished piece 1 at 20140125 16:29:09
piece handle=/oradata/orcl/databak/9qouvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_6: backup set complete, elapsed time: 00:00:07
channel ORA_DISK_5: finished piece 1 at 20140125 16:29:16
piece handle=/oradata/orcl/databak/9pouvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_5: backup set complete, elapsed time: 00:00:14
channel ORA_DISK_2: finished piece 1 at 20140125 16:29:19
piece handle=/oradata/orcl/databak/9mouvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:17
channel ORA_DISK_4: finished piece 1 at 20140125 16:29:22
piece handle=/oradata/orcl/databak/9oouvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_4: backup set complete, elapsed time: 00:00:20
channel ORA_DISK_3: finished piece 1 at 20140125 16:29:47
piece handle=/oradata/orcl/databak/9nouvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_3: backup set complete, elapsed time: 00:00:45
channel ORA_DISK_1: finished piece 1 at 20140125 16:29:54
piece handle=/oradata/orcl/databak/9louvdue_1_1 tag=TAG20140125T162902 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:52
Finished backup at 20140125 16:29:54
Starting Control File and SPFILE Autobackup at 20140125 16:29:54
piece handle=/oradata/orcl/databak/c-1347935162-20140125-12 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 16:29:57
因為只有6個檔案，所以，只實際使用了6個通道。備份時間為57秒（16:29:00至16:29:57），和手工指定6通道時的用時完全一樣。
綜上，我們可以看出，這個並行度的引數與手工指定通道的作用是類似的。只不過一個是由RMAN自動分配，一個由人工指定。
FILESPERSET這個引數又是做什麼用的呢？還是來做實驗。
我們把並行度改回2
RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 2 BACKUP TYPE TO BACKUPSET;
old RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 7 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters:
CONFIGURE DEVICE TYPE DISK PARALLELISM 2 BACKUP TYPE TO BACKUPSET;
new RMAN configuration parameters are successfully stored
根據我們前邊做實驗的經驗，如果這時執行backup database；命令，會自動通過兩個通道來備份。
如果我們執行 backup database filesperset 2; 又會是什麼結果呢？
RMAN> backup database filesperset 2;
Starting backup at 20140125 16:58:48
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=158 devtype=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: sid=147 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 16:58:48
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 16:58:48
channel ORA_DISK_2: finished piece 1 at 20140125 16:58:55
piece handle=/oradata/orcl/databak/9vouvfm8_1_1 tag=TAG20140125T165848 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:07
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 16:58:55
channel ORA_DISK_1: finished piece 1 at 20140125 16:59:40
piece handle=/oradata/orcl/databak/9uouvfm8_1_1 tag=TAG20140125T165848 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:52
channel ORA_DISK_2: finished piece 1 at 20140125 16:59:40
piece handle=/oradata/orcl/databak/a0ouvfmf_1_1 tag=TAG20140125T165848 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:45
Finished backup at 20140125 16:59:40
Starting Control File and SPFILE Autobackup at 20140125 16:59:40
piece handle=/oradata/orcl/databak/c-1347935162-20140125-14 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 16:59:43
看到了嗎，加了filesperset 2 這個引數後，每次每通道只讀取2個資料檔案了。最終6個資料檔案，生成了3個備份檔案。
換句話說，每個備份集裡，最多隻能包含兩個原始檔。如果我們設為 filesperset 1的話，由於一個備份集中只能有1個原始檔，所以，實驗環境下的這6個資料檔案就要生成6個備份集了。
驗證一下：
RMAN> backup database filesperset 1;
Starting backup at 20140125 17:01:01
using channel ORA_DISK_1
using channel ORA_DISK_2
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 17:01:01
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 17:01:01
channel ORA_DISK_2: finished piece 1 at 20140125 17:01:08
piece handle=/oradata/orcl/databak/a3ouvfqd_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:07
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 17:01:08
channel ORA_DISK_1: finished piece 1 at 20140125 17:01:43
piece handle=/oradata/orcl/databak/a2ouvfqd_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:42
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00004 name=/oradata/orcl/users01.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 17:01:43
channel ORA_DISK_2: finished piece 1 at 20140125 17:01:43
piece handle=/oradata/orcl/databak/a4ouvfqk_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:35
channel ORA_DISK_2: starting full datafile backupset
channel ORA_DISK_2: specifying datafile(s) in backupset
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel ORA_DISK_2: starting piece 1 at 20140125 17:01:43
channel ORA_DISK_1: finished piece 1 at 20140125 17:01:44
piece handle=/oradata/orcl/databak/a5ouvfrn_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel ORA_DISK_1: starting piece 1 at 20140125 17:01:44
channel ORA_DISK_2: finished piece 1 at 20140125 17:01:44
piece handle=/oradata/orcl/databak/a6ouvfrn_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:01
channel ORA_DISK_1: finished piece 1 at 20140125 17:01:45
piece handle=/oradata/orcl/databak/a7ouvfro_1_1 tag=TAG20140125T170101 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 20140125 17:01:45
Starting Control File and SPFILE Autobackup at 20140125 17:01:46
piece handle=/oradata/orcl/databak/c-1347935162-20140125-15 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 17:01:47
果然。


現在，我們回過頭來，把當需要備份的檔案個數為質數時，如何在多個通道中分配的實驗做了。
為了滿足這個條件，我們在資料庫中再新增一個表空間，並在該表空間中新增一個資料檔案，從而形成7個資料檔案。
SQL> create tablespace demo datafile '/oradata/orcl/demo01.dbf' size 10M;
Tablespace created.
SQL> create table demo (id int) tablespace demo;
Table created.
SQL> insert into demo values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select file_name,file_id,bytes/1024/1024 "size(M)" from dba_data_files;
FILE_NAME                                           FILE_ID    size(M)
---------------------------------------- ---------- ----------
/oradata/orcl/system01.dbf                1                  400
/oradata/orcl/undotbs01.dbf              2                 320
/oradata/orcl/sysaux01.dbf                3                   190
/oradata/orcl/users01.dbf                  4                 21.25
/oradata/orcl/hrtbs01.dbf                   5                    10
/oradata/orcl/demo01.dbf                 6                     10
/oradata/orcl/system02.dbf                7                     10
7 rows selected.
再回到RMAN中，以手工指定4個通道的方式來進行資料庫備份。
MAN> run
{ allocate channel c1 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c2 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c3 device type disk format '/oradata/orcl/databak1/%U';
 allocate channel c4 device type disk format '/oradata/orcl/databak1/%U';
backup database;
release channel c1;
release channel c2;
release channel c3;
release channel c4;
}2> 3> 4> 5> 6> 7> 8> 9> 10> 11>
released channel: ORA_DISK_1
released channel: ORA_DISK_2
allocated channel: c1
channel c1: sid=158 devtype=DISK
allocated channel: c2
channel c2: sid=147 devtype=DISK
allocated channel: c3
channel c3: sid=138 devtype=DISK
allocated channel: c4
channel c4: sid=137 devtype=DISK
Starting backup at 20140125 17:41:56
channel c1: starting full datafile backupset
channel c1: specifying datafile(s) in backupset
input datafile fno=00001 name=/oradata/orcl/system01.dbf
channel c1: starting piece 1 at 20140125 17:41:56
channel c2: starting full datafile backupset
channel c2: specifying datafile(s) in backupset
input datafile fno=00002 name=/oradata/orcl/undotbs01.dbf
input datafile fno=00007 name=/oradata/orcl/system02.dbf
channel c2: starting piece 1 at 20140125 17:41:56
channel c3: starting full datafile backupset
channel c3: specifying datafile(s) in backupset
input datafile fno=00003 name=/oradata/orcl/sysaux01.dbf
input datafile fno=00006 name=/oradata/orcl/demo01.dbf
channel c3: starting piece 1 at 20140125 17:41:56
channel c4: starting full datafile backupset
channel c4: specifying datafile(s) in backupset
input datafile fno=00004 name=/oradata/orcl/users01.dbf
input datafile fno=00005 name=/oradata/orcl/hrtbs01.dbf
channel c4: starting piece 1 at 20140125 17:41:56
channel c4: finished piece 1 at 20140125 17:41:57
piece handle=/oradata/orcl/databak1/agouvi74_1_1 tag=TAG20140125T174156 comment=NONE
channel c4: backup set complete, elapsed time: 00:00:01
channel c2: finished piece 1 at 20140125 17:42:12
piece handle=/oradata/orcl/databak1/aeouvi74_1_1 tag=TAG20140125T174156 comment=NONE
channel c2: backup set complete, elapsed time: 00:00:16
channel c3: finished piece 1 at 20140125 17:42:27
piece handle=/oradata/orcl/databak1/afouvi74_1_1 tag=TAG20140125T174156 comment=NONE
channel c3: backup set complete, elapsed time: 00:00:31
channel c1: finished piece 1 at 20140125 17:42:34
piece handle=/oradata/orcl/databak1/adouvi74_1_1 tag=TAG20140125T174156 comment=NONE
channel c1: backup set complete, elapsed time: 00:00:38
Finished backup at 20140125 17:42:34
Starting Control File and SPFILE Autobackup at 20140125 17:42:34
piece handle=/oradata/orcl/databak/c-1347935162-20140125-18 comment=NONE
Finished Control File and SPFILE Autobackup at 20140125 17:42:37
released channel: c1
released channel: c2
released channel: c3
released channel: c4
實驗證明，當需備份的檔案數不能均分至多個通道時，RMAN會以一種近似平均的方法來處理。那麼為什麼6個檔案4個通道時，RMAN沒有采用1-1-2-2的方式來使用4個通道呢？個人推測是由於當按這種方式分配時，最多的一個通道上還是要有2個檔案，那麼這時，就不如把6個檔案分配在3個通道上（即2-2-2的分配方式）即節省了通道數，又能保證總體的備份時間不會延長。同時，在進行檔案分配時，檔案的大小，也是其進行分配的一個考慮因素，RMAN會在首先保證各通道處理的檔案個數接近的前提下，使每個通道上分配到的總的檔案大小也儘量均衡。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/22207394/viewspace-1075385/，如需轉載，請註明出處，否則將追究法律責任。

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