Oracle DataGuard Instructor 之Redo Transport Services《2》
What to Do If Errors Occur
                                    王清清

5.5 What to Do If Errors Occur

To handle archiving failures, you can use the REOPEN, MAX_FAILURES, and ALTERNATE attributes of the LOG_ARCHIVE_DEST_n parameter to specify what actions are to be taken when archival processing to a destination fails. These actions include:

·  Retrying the archival operation to a failed destination after a specified period of time, up to a limited number of times

·  Using an alternate or substitute destination

·  Controlling the number of attempts to reestablish communication and resume sending redo data to a failed destination.

5.5.1 Retrying the Archival Operation

Use the REOPEN attribute to determine if and when the ARCn process or the LGWR process attempts to transmit redo data again to a failed destination following an error.

Use the REOPEN=seconds attribute to specify the minimum number of seconds that must elapse following an error before the archiving process will try again to access a failed destination. The default value is 300 seconds. The value set for the REOPEN attribute applies to all errors, not just connection failures. You can turn off the option by specifying REOPEN=0, which prevents the destination from being retried after a failure occurs.

If transmission to the alternate destination fails and the REOPEN attribute is set to zero (0), redo transport services will attempt to send redo data to the alternate destination the next time redo data is archived.

5.5.2 Using an Alternate Destination

The ALTERNATE attribute defines an alternate archiving destination that can be used when the original archiving destination fails. If no alternate destination is specified, the destination does not automatically change to another destination upon failure.

Figure 5-6 shows a scenario where redo data is archived to a local disk device. If the original destination device becomes full or unavailable, the archival operation is automatically redirected to the alternate destination device.

The REOPEN attribute takes precedence over the ALTERNATE attribute. The alternate destination is used only if one of the following conditions is true:

·   A value of zero (0) is specified for the REOPEN attribute.

·   A nonzero REOPEN attribute and a nonzero MAX_FAILURE count have been exceeded.

The ALTERNATE attribute takes precedence over the MANDATORY attribute. This means that a destination fails over to a valid alternate destination even if the current destination is mandatory.

5.5.3 Controlling the Number of Retry Attempts

Use the MAX_FAILURE attribute to specify the maximum number of consecutive times that redo transport services attempt to transmit redo data to a failed destination. To limit the number of consecutive attempts that will be made to reestablish communication with a failed destination, use the REOPEN attribute in conjunction with the MAX_FAILURE attribute. Once the specified number of consecutive attempts is exceeded, the destination is treated as if the REOPEN attribute was set to zero.

The REOPEN attribute is required when you use the MAX_FAILURE attribute. Example 5-7 shows how to set a retry time of 60 seconds and limit retries to 3 attempts.

Example 5-7 Setting a Retry Time and Limit

LOG_ARCHIVE_DEST_1='LOCATION=/arc_dest REOPEN=60 MAX_FAILURE=3'

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