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Configuring an Oracle Database to Send Redo Data


This section describes how to configure an Oracle database to send redo data to a redo transport destination.

The LOG_ARCHIVE_DEST_n database initialization parameter (where n is an integer from 1 to 10) is used to specify the location of a local archive redo log or to specify a redo transport destination. This section describes the latter use of this parameter.

There is a LOG_ARCHIVE_DEST_STATE_n database initialization parameter (where n is an integer from 1 to 10) that corresponds to each LOG_ARCHIVE_DEST_n parameter. This parameter is used to enable or disable the corresponding redo destination. Table 6-1 shows the valid values that can be assigned to this parameter.

Table 6-1 LOG_ARCHIVE_DEST_STATE_n Initialization Parameter Values

Value Description
ENABLE Redo transport services can transmit redo data to this destination. This is the default.
DEFER Redo transport services will not transmit redo data to this destination.
ALTERNATE This destination will become enabled if communication to its associated destination fails.

A redo transport destination is configured by setting the LOG_ARCHIVE_DEST_n parameter to a character string that includes one or more attributes. This section briefly describes the most commonly used attributes. See Chapter 15 for a full description of all LOG_ARCHIVE_DEST_n parameter attributes.

The SERVICE attribute, which is a mandatory attribute for a redo transport destination, must be the first attribute specified in the attribute list. The SERVICE attribute is used to specify the Oracle Net service name used to connect to a redo transport destination. See the Oracle Database Net Services Administrator’s Guide for information about Oracle Net service names.

The SYNC attribute is used to specify that the synchronous redo transport mode be used to send redo data to a redo transport destination.

The ASYNC attribute is used to specify that the asynchronous redo transport mode be used to send redo data to a redo transport destination. The asynchronous redo transport mode will be used if neither the SYNC nor the ASYNC attribute is specified.

The NET_TIMEOUT attribute is used to specify how long the LGWR process will block waiting for an acknowledgement that redo data has been successfully received by a destination that uses the synchronous redo transport mode. If an acknowledgement is not received within NET_TIMEOUT seconds, the redo transport connection is terminated and an error is logged.

Oracle recommends that the NET_TIMEOUT attribute be specified whenever the synchronous redo transport mode is used, so that the maximum duration of a redo source database stall caused by a redo transport fault can be precisely controlled. SeeSection 6.3.2 for information about monitoring synchronous redo transport mode response time.

The AFFIRM attribute is used to specify that redo received from a redo source database is not acknowledged until it has been written to the standby redo log. The NOAFFIRM attribute is used to specify that received redo is acknowledged without waiting for received redo to be written to the standby redo log.

The DB_UNIQUE_NAME attribute is used to specify the DB_UNIQUE_NAME of a redo transport destination. The DB_UNIQUE_NAMEattribute must be specified if the LOG_ARCHIVE_CONFIG database initialization parameter has been defined and its value includes a DG_CONFIG list.

If the DB_UNIQUE_NAME attribute is specified, its value must match one of the DB_UNIQUE_NAME values in the DG_CONFIG list. It must also match the value of the DB_UNIQUE_NAME database initialization parameter at the redo transport destination. If either match fails, an error is logged and redo transport will not be possible to that destination.

The VALID_FOR attribute is used to specify when redo transport services transmits redo data to a redo transport destination. Oracle recommends that the VALID_FOR attribute be specified for each redo transport destination at every site in a Data Guard configuration so that redo transport services will continue to send redo data to all standby databases after a role transition, regardless of which standby database assumes the primary role.

The REOPEN attribute is used to specify the minimum number of seconds between automatic reconnect attempts to a redo transport destination that is inactive because of a previous error.

The COMPRESSION attribute is used to specify that redo data is transmitted to a redo transport destination in compressed form when resolving redo data gaps. Redo transport compression can significantly improve redo gap resolution time when network links with low bandwidth and high latency are used for redo transport. Redo gap resolution is discussed in Section 6.3.3.

The following example uses all of the LOG_ARCHIVE_DEST_n attributes described in this section. Two redo transport destinations are defined and enabled. The first destination uses the asynchronous redo transport mode. The second destination uses the synchronous redo transport mode with a 30-second timeout. A DB_UNIQUE_NAME has been specified for both destinations, as has the use of compression when resolving redo gaps. If a redo transport fault occurs at either destination, redo transport will attempt to reconnect to that destination, but not more frequently than once every 60 seconds.

DB_UNIQUE_NAME=BOSTON
LOG_ARCHIVE_CONFIG='DG_CONFIG=(BOSTON,CHICAGO,DENVER)'
LOG_ARCHIVE_DEST_2='SERVICE=CHICAGO ASYNC NOAFFIRM VALID_FOR=(ONLINE_LOGFILE,  PRIMARY_ROLE) REOPEN=60 COMPRESSION=ENABLE  DB_UNIQUE_NAME=CHICAGO'
LOG_ARCHIVE_DEST_STATE_2='ENABLE'
LOG_ARCHIVE_DEST_3='SERVICE=DENVER SYNC AFFIRM NET_TIMEOUT=30 VALID_FOR=(ONLINE_LOGFILE,PRIMARY_ROLE) REOPEN=60 COMPRESSION=ENABLE  DB_UNIQUE_NAME=DENVER'
LOG_ARCHIVE_DEST_STATE_3='ENABLE'

 

 

Taken from http://download.oracle.com/docs/cd/B28359_01/server.111/b28294/log_transport.htm

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December 30, 2010 - Posted by | Data Guard

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