Shulou(Shulou.com)06/02 Report--

PARALLELISM

We can also use the parallelism parameter to specify how many channels are created "automatically" at the same time:

RMAN > configure device type disk parallelism 3

Indicates that starting three channels can speed up backup recovery.

By default, the parallelism of the auto-assigned channel is 1, if you set the parallel channel by setting PARALLELISM

Is 2, then in the run block, if you do not specify a channel through the ALLOCATE CHANNEL command alone, it defaults

Using 2 parallel channels, if you specify several ALLOCATE CHANNEL in the run command block, then the rman is in the

The backup command will be based on the channel you set, regardless of how many parallel channels are configured in the configure.

It is important to note that there is a FILESPERSET parameter in the backup command, which refers to every rman established

The maximum number of data files that can be contained in a backup set (note: it does not refer to backup slices, that is, backed-up files). The default value of this parameter is 64.

If the parameter value is not specified in the backup command, rman will only use the first channel to perform the backup, and the other channels

Will be idle. There is also a size relationship between the number of channels and the FILESPERSET value, and the logic is a little more complicated.

For example, if the number of datafiles is 25 and the number of FILESPERSET is 8, then 4 backupset are generated when backing up the database, and each backup set contains 8 data files.

-define the number of channels in parallel, and channels define channel attributes.

Example 1:

RMAN > configure device type disk parallelism 4

RMAN > configure channel 1 device type disk

RMAN > configure channel 2 device type disk

Note: in the above configuration, four channels will be opened, channel 1, 2, and 3, 4, with the user's configuration and default configuration.

Example 2:

RMAN > configure device type disk parallelism 3

RMAN > configure channel 1 device type disk

RMAN > configure channel 2 device type disk

RMAN > configure channel 3 device type disk

RMAN > configure channel 4 device type disk

Note: at this time, RMAN will ignore the setting of parallelism, depending on the channel set by the user.

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Reprint:

How does oracle choose between filesperset and channel? Let's see what the experts say.

-- biti_rainy

Filesperset = filesper backupset

There are 10 datafiles,filesperset = 4

10, 4, 2. 5.

Generate 3 backupset when you back up the database

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-- piner

Filesperset means that each backup set can back up up to several data files or archive logs.

A backup set can have more than one backup.

Backups such as data files cannot span backup sets but can span backup slices.

So it is correct to say that the backup set contains a certain data file.

-- blog author joins:

Note: maxpiecesize is used to set the size of the backup slice. For example, if the maximum backup size is 2000m, a 5G data file must be backed up across backup slices, but a data file cannot be backed up across multiple backup sets. Usually a channel corresponds to a backup set.

CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' MAXPIECESIZE 2000 M

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-- husthxd

Using filesperset to control the size of backup set

When the filesperset parameter is specified, rman compares the filesperset with the automatically calculated value (number of files per assigned channel)

And take the smaller value to ensure that all channels are used.

If the number of files specified or implied by combining backupSpec statements is larger than filesperset

Then rman creates multiple backup sets to maintain the correct rate (ratio)

If you do not specify the value calculated by the filesperset,rman comparison (number of files divided by assigned channels) and the default value of 64

And take the smaller value to ensure that all channels are available.

Rman usually attempts to create enough backup sets to give all assigned channels something to do.

One exception is that there are more channels than files to back up.

Blog authors understand examples:

For example:

A. filesperset is set to 6, the number of data files is 30, and the channel data is 4. Each can be obtained by 30 picks 4.

A backup set can contain 8 files, with a smaller value of 6 in 6 and 8, so there must be something to do for all 4 channels if there are 5 backup sets in 30 Universe.

b. If you do not specify filesperset, assume that the number of data files is 30 and the channel data is 4.

It is concluded that each backup set can contain 8 files, compare 8 with the default value of 64, and if we take the smaller 8, we can also ensure that all four channels have something to do.

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