Creating a backup of your data is a simple, essential component
of any serious installation. Adaptive Server Anywhere includes utilities
to help minimize data loss in case your data becomes corrupt as
a result of media failure, power outage, or other failure. Backups of Adaptive Server Anywhere databases can be performed
through the dbbackup command line utility, SQL, or Sybase Central.
Both full backups and incremental backups can be performed, and
they can be performed either online or offline (that is, whether
the server is running or not, respectively). In addition, backups
can be performed both from the server side and from the client side. A full backup makes copies of the main database file and the
transaction log file. While it's the most basic and essential type
of backup, it usually isn't practical to regularly perform full backups
of large databases. As a result, incremental backups are commonly
used. An incremental backup makes a copy of the transaction log
alone. It takes place as part of a cycle that begins with a full
backup, which is then followed by a given number of incremental backups.
Since only the transaction log is copied, an incremental backup
uses less time and resources, making it particularly suited for
large databases. Keep in mind, though, that the more time you leave
between full backups, the greater the risk of losing data in the
event that one of the transaction logs becomes unusable. An online backup is performed without stopping the database
server. It provides a consistent snapshot of the database, even
as the database is modified. Online backups are useful for databases
with high availability requirements, but they won't complete until
all active transactions are complete. In contrast, offline backups are performed once the database
server has been shut down. They're useful for when the database
can be taken down on a regular basis. You make offline backups simply
by copying the pertinent files to another location using the cp
command in a terminal window. In either case, both full and incremental backups can be performed. An online backup can be performed from a client using the dbbackup command
line utility. This is known as a client-side backup, and it puts
a backup of the database on the client machine. An online backup can also be performed on the server by issuing
the BACKUP statement in SQL. Server-side backups are generally faster,
owing to the fact that client-side backups usually depend upon transport
across networks. The command line utility for making a backup of your database
is dbbackup. Its syntax is as follows: dbbackup [ switches ] directory directory specifies a destination directory for the backup
files. Some useful switches include the following: -c is used to specify a connection
string to the database to be backed up -d creates a backup of the main database file only -t creates a backup of the transaction log only -r renames any previous transaction log backups
and creates a new one. It is necessary for replication systems. -x deletes any previous transaction log backups
and creates a new one. It should not be used in replication systems.
For example, if you were creating your first backup, you would
want to create a full backup of MyDatabase. To put it in ./backups,
use the following command: dbbackup -c "uid=DBA;pwd=SQL;dbn=MyDatabase" ./backups The next few backups could be incremental backups, so use
the following: dbbackup -t -r -c "uid=DBA;pwd=SQL;dbn=MyDatabase" ./backups If you prefer to back up your database from Interactive SQL,
the SQL statement is BACKUP DATABASE. You must have DBA authority
to use BACKUP DATABASE, whose syntax is as follows: BACKUP DATABASE DIRECTORY backup-directory
[ WAIT BEFORE START ]
[ DBFILE ONLY ]
[ TRANSACTION LOG ONLY ]
[ TRANSACTION LOG RENAME [ MATCH ] ]
[ TRANSACTION LOG TRUNCATE ] |
To make a backup from Sybase Central, open the Utilities folder
under "Adaptive Server Anywhere 7" and double-click "Backup Database"
to open a dialog box which will guide you through the backup process. You should regularly use either Sybase Central, SQL, or the
dbvalid command line utility to validate a backup of your database
in read-only mode, and, if errors are found, make repairs against
the original database. Never make changes to
a backup database! To read more about validation, see "Validating
a database" and "Validating a transaction log" under the Backup
and Data Recovery chapter of the Adaptive Server Anywhere User's
Guide. Depending on the way your database and its backups are set
up, and the status of your files after a media failure, there are
several possible processes involved in how you go about recovering
data. For information on how to recover data in various situations,
see the Backup and Data Recovery chapter of the Adaptive Server
Anywhere User's Guide. | |
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