SQL Remote User's Guide
SQL Remote Administration
Running the Message Agent
SQL Remote replication places new requirements on data recovery practices at consolidated database sites. Standard backup and recovery procedures enable recovery of data from system or media failure. In a replication installation, even if such recovery is achieved, the recovered database can be out of synch with remote databases. This can require a complete resynchronization of remote databases, which can be a formidable task if the installation involves large numbers of databases.
In short, recovery of the consolidated database from a failure at the consolidated site is only part of the task of recovering the entire replication installation.
Protection of the replication system against media failures has two aspects:
Backup and log management Solid backup procedures and log management procedures for the consolidated database server are an essential part of recovery plans. Backup procedures protect against media failure on the database device. Using a transaction log mirror protects against media failure on the transaction log device.
For more information about backup and log management procedures, see the sections Transaction log and backup management and Adaptive Server Enterprise transaction log and backup management.
Message Agent configuration The Message Agent command-line options provide ways for you to tune Message Agent behavior to match your backup and recovery requirements.
Message Agent configuration is discussed in the following pages.
By default, the Message Agent processes all committed transactions. When the Message Agent is run with the -u option, only transactions that have been backed up by the database backup commands are processed.
For Adaptive Server Anywhere, transaction log backup is carried out using Sybase Central or the dbbackup utility, or off-line copying and renaming of the log file. For Adaptive Server Enterprise, transaction log backup is carried out using the dump transaction statement.
By sending only backed-up transactions, the replication installation is protected against media failure on the transaction log. Maintaining a mirrored transaction log also accomplishes this goal.
The -u option provides additional protection against total site failure, if backups are carried out to another site.