User's Manual

Chapter 10. SQL Remote Administration
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” on page 249
and “Adaptive Server Enterprise transaction log and backup
management” on page 272.
♦ 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.
Replicating only
backed-up transactions
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.
Ensuring consistent Message Agent settings
Some Message Agent settings need to be the same throughout an
installation, and so should be set before deployment. This section lists the
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