Data Guard log management policy tips Oracle Database Tips by Donald BurlesonDecember 9, 2015

Oracle Data Guard - Log Management Services

Log Management Policies

Log management policies play an important role in the disaster recovery strategy. These policies are largely guided by the importance of data in the database and the ability to recover the data using other sources like re-loading data from flat files, etc.

In a Data Guard environment, the log management policies are implemented using attributes of the log_archive_dest_n parameter. The attributes like MANDATORY, REOPEN, and ALTERNATE can be used to control the transmission of archived redo data. In this section, the attributes of the log_archive_dest_n and log_archive_dest_state_n parameters will be presented.

Factors Influencing Log Transport Policies

The log_archive_dest_n parameter has a vast number of attributes to control the working of log transfer services. The following attributes are important for setting up policies of log management services:

Online Redo Logs Reuse Policy

Online Redo logs on the primary database will be taken up for reuse based on the status of archiving to the log archive destinations. The archiving destinations can be set as MANDATORY or OPTIONAL destinations. For MANDATORY destinations, archiving should be completed before the online redo logs of the primary database can be marked for reuse. On the contrary, for OPTIONAL destinations, the log writer on the primary database will not wait for archiving to finish.

Log Management Services

A Sample Log Management Policy

LOG_ARCHIVE_DEST_1='LOCATION=/oracle/appsdb/arch MANDATORY
REOPEN=90 MAX_FAILURE=2 ALTERNATE=LOG_ARCHIVE_DEST_4'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_2='SERVICE=appsstdby1
DEPENDENCY=LOG_ARCHIVE_DEST_1'
LOG_ARCHIVE_DEST_STATE_2=ENABLE
LOG_ARCHIVE_DEST_3='SERVICE=appsstdby2 REOPEN=90 MAX_FAILURE=5'
LOG_ARCHIVE_DEST_STATE_3=ENABLE
LOG_ARCHIVE_DEST_4='LOCATION=/oracle2/appsdb/arch'
LOG_ARCHIVE_DEST_STATE_4=ALTERNATE

According to this policy, the primary database physically archives the log file to the local destination on volume /oracle and to the Oracle instance identified by the service name appsstdby2. The local archival destination #1 is a mandatory destination. The primary database will halt if archival to this destination does not succeed. The log transfer service on the primary database will make two attempts to archive the redo log files to this destination as indicated by the max_failure parameter.