Eloquence Database Backup
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There are two supported procedures to perform a backup of the
Eloquence database environment.
- Off-line backup
- The database server process is shut down in order to make a backup.
Applications can no longer use the database until the backup is
finished.
- On-line backup
- The backup is made while the database is active. Applications
can access and modify the database.
The Eloquence database supports on-line backup, allowing the
database to be available during backup (at reduced performance).
Other backup procedures (besides the ones mentioned above)
are likely to cause a corrupted backup or no backup at all
(e.g. fbackup on HP-UX refuses to backup modified files).
In addition, there is a procedure to backup or restore a single
database.
- dbstore / dbrestore
- The dbstore / dbrestore functionality allows transfer of a
single database from a database environment to a file or tape
device. This makes it easy to save a snapshot of a database or
move a single database to another system.
An off-line backup takes place when the eloqdb6 is not active.
You need to shut down the eloqdb6 process by either executing
- dbctl -u dba shutdown
- or /sbin/init.d/eloq6 stop on HP-UX or Linux
- or net stop eloqdb6 on Windows NT.
After the eloqdb6 server has been shut down you should consider
to execute dblogreset before performing the backup.
This resets the log volume to its minimum size and makes sure
all transactions are applied.
If the database was not shutdown cleanly, the log volumes contain
important data needed to recover the data base environment.
Without the log information your databases may be lost.
The dblogreset utility makes sure that the log information
is applied to your data volume(s).
The backup should cover all data and log volumes which are part
of the database environment. While it is possible to re-create
a missing log volume if the server was shutdown cleanly (or
dblogreset was executed) we do not recommend this.
Please note: The log volume(s) might contain important information
(your data) and you should handle them with the same care as your data.
Otherwise your database environment may become unusable.
Example backup script:
/sbin/init.d/eloq6 stop
/opt/eloquence6/bin/dblogreset
tar -cf /dev/rmt/0m /data/db
/sbin/init.d/eloq6 start
This example performs a backup of the default database server environment.
The eloqdb6 process is shut down, the log volumes are reset to initial
state (optional), the volume files are backed up and the server process
is restarted.
This example assumes the volume files reside in the directory /data/db
Warning: Using fackup on HP-UX to backup a database environment
while the server is active will most likely not work and you
may end up with no usable backup. Fbackup on HP-UX verifies that
a file is not changed during backup and will take multiple attempts to
backup the file. It will ultimately fail and the volume file is not
backed up. Unless in on-line backup mode the eloqdb6 may change the
volume files at any time, even if no users are active.
To recover from an off-line backup, make sure the database server process
is not active and restore all data and log volumes which are part of
the database environment.
When recovering to a temporary location you may need to
create a server configuration file (eloqdb6.cfg) or modify an existing one.
Please make sure the volume files in the configuration file refer
to the recovered files.
If the log volumes are lost and your database was shut
down cleanly, you can re-create any missing log volume with the
dbvolextend command (see below).
Please note: If your database was not shut down cleanly
and your log volume is lost your database may be damaged.
If your log volumes are lost (e.g. due to a disk failure)
and your database was shut down cleanly,
you can re-create any missing log volume with the dbvolextend command.
Execute dbvolextend -t log /path/to/logvol for
each missing log volume file. The log volume file name(s) must match
already existing entries in the server configuration file.
Assumed your database environment was configured to use two
log volumes named /db/log/log01.vol and /db/log/log02.vol
the following commands can be used to re-create the log
volumes:
dbvolextend -t log /db/log/log01.vol
dbvolextend -t log /db/log/log02.vol
Since any previous log volume properties (like min. or max. size)
are lost you may need to specify additional options to dbvolextend
or use dbvolchange to modify the volume properties.
You can use dbvoldump to display the volume information.
After the log volume(s) are re-created, you can start the eloqdb6
server process.
An on-line backup takes place when the eloqdb6 is active.
The on-line backup is initiated with the dbctl backup start
command which causes the eloqdb6 process to enter on-line backup mode.
When entering on-line backup mode, eloqdb6 creates a transaction
consistent snapshot of the data volume(s) and makes sure the
data volume(s) do not change during the backup.
All changes to the data volume(s) are temporarily redirected to
the log volume(s).
The data volume(s) can then be backed up by an arbitrary backup tool
(e.g. fbackup, tar, cp, etc.).
Once the backup is complete, the on-line backup mode is terminated
by the dbctl backup stop command.
This causes the eloqdb6 server process to update all pending
data which was temporarily redirected to the log volume(s).
Please note: The eloqdb6 performance is reduced in on-line backup
mode and the log volume(s) must provide sufficient space for all
modifications during backup.
Log volumes do not need to be backed up in an on-line backup.
They are changing constantly and are not used for recovery.
Please note: When using fackup on HP-UX it is recommended to exclude
the log volume(s) from the backup. Fbackup issues a warning note if a
file is changed during backup. It may take multiple attempts to
backup the log volume.
In case the eloqdb6 server is shut down during on-line backup
mode (or a failure occurs) the data volume(s) are updated
automatically when the server is restarted.
Suppose you have data volume(s) located in the directory
/db/data and log volume(s) located in the directory
/db/log. Use the following commands to backup your data volume(s):
dbctl -u dba backup start
tar -cf /dev/rmt/0m /db/data
dbctl -u dba backup stop
Please note: You should consider to not backup your log volume(s)
in on-line backup mode - they are not used to recover
the database. They only take space on your backup media.
Please Note: If multiple eloqdb6 instances are active on one
system, on-line backup must be activated for each database
server environment separately.
To recover the database to the state when the on-line backup
was started, please make sure the database server process is
not active and recover the data volume(s) from the backup media.
If your log volumes are still present, you are ready to start
the eloqdb6 server. The contents of the log volume(s) are ignored.
If your log volume(s) are lost (e.g. due to a disk failure)
you can use dbvolextend to re-create your log volume(s).
Execute dbvolextend -t log /path/to/logvol for
each missing log volume file. The log volume file name(s) must match
already existing entries the server configuration file.
Assumed your database environment was configured to use two
log volumes named /db/log/log01.vol and /db/log/log02.vol
the following commands can be used to re-create the log
volumes:
dbvolextend -t log /db/log/log01.vol
dbvolextend -t log /db/log/log02.vol
Since any previous log volume properties (like min. or max. size)
are lost you may need to specify additional options to dbvolextend
or use dbvolchange to modify the volume properties.
You can use dbvoldump to display the volume information.
After the log volume(s) are re-created, you can start the eloqdb6
server process.
Database utilities which modify the data volume can not
be used immediately if the eloqdb6 server was shut down or crashed
while in on-line backup mode.
The log data (all committed transactions since entering
on-line backup mode) has been temporarily stored in the log volume
and must be recovered before database utilities are allowed to
modify the data volume.
Otherwise all transactions pending since starting the on-line backup
would be lost.
The following message is output by the affected utilities:
NOTE: Database environment has been shutdown during
on-line backup. Please restart the database server
once in order to recover from on-line backup mode,
then reapply this command.
To recover the information from the log volume, please either
run dblogreset or start the eloqdb6 server. Afterwards you can
use the utility program as planned.
Affected tools are:
- dbvolextend
- dbvolchange
- dbfsck (in write mode)
When on-line backup mode is activated and
forward logging is active, a new log segment
is started. In case the database server is configured to manage the
forward log files, a new forward log file is created. This new forward
log file covers all changes since the on-line backup has started.
After the on-line backup has finished successfully, all previous
forward log files (which existed before the on-line backup mode was
started) can be removed as they are covered by the backup.
The dbstore / dbrestore functionality allows transfer of a single
database from a database environment to a file or tape device.
This makes it convenient to save a snapshot of a database or move
a single database to another system.
Please note: This is not a recommended strategy to backup your
database environment.
The on-line backup and off-line backup methods presented above provide
a consistent backup of your complete database environment which
includes all your databases and additional configuration (users, passwords,
database permission groups and user assignments).
Dbstore only backs-up a single database.
The dbstore and dbrestore operation is executed by the
database server and the archive files are written by
the server process. The dbctl utility is only used to initiate the process.
Backup files are written to and read from pre-configured paths
(called "server devices") to avoid unauthorized access to the
server system.
A "server device" could either be a single file, a directory or a device.
When no server devices are configured, dbstore and dbrestore operation is
refused by the server.
The example below defines two "server devices". The device "tape"
points to a tape device file, the device "backup" points to a directory
which is intended to hold the backup files.
[devices]
Tape = /dev/rmt/c1t0d0BEST
Backup = /data/backup
The dbctl utility is used to initiate a store or restore operation.
dbctl dbstore database target
dbctl dbrestore [/info] source [new_database_name]
The dbctl dbstore command transfers a single database
to the target "device" which must be defined in the server configuration
file. In order to store a database, database admin (dadmin) or
server admin (dba) capabilities are required. Exclusive access
to the database is required.
The target specification is either the name of a configured server
device or the name of a server device and a filename separated by a slash.
The dbctl dbrestore command restores a single database
from a source device which must be defined in the server configuration
file. The database may not already exist.
Server administration (dba) capabilities are required in order to
restore a database.
The source specification is either the name of a configured server device
or the name of a server device and a filename separated by a slash.
If the optional /info argument is present, information on the
archive is returned and the archive is not restored.
If the optional new_database_name argument is present, the database
is restored to the specified name instead of the original database name.
Since dbstore copies the database to a binary archive, the archive
occupies the same disk space as the database. The archive can only
be restored to a system with the same byte order.
For example, you cannot create an archive on Linux and restore it
on a HP-UX system. You need to use dbexport/dbimport to move a
database to a different architecture.
When a database is restored, the association between database
permission groups and server users ("sysmember") is deleted for
all but the default "dba" and "public" users.
Since the database could be restored on a different server
this could otherwise lead to inconsistencies or unauthorized access
to your data.
Backup files created by dbctl dbstore are limited to 2 GB on the
HP-UX and Linux platforms when writing to the file system.
A dbctl dbstore will fail when the backup file exceeds 2 GB.
The solution is to compress the backup on the fly which might
also improve performance as the disk I/O is reduced significantly.
See below for more information.
Assumed you defined a server device "tape" in your server configuration
file the command below dumps the database payrol to the tape device:
dbctl -u dba dbstore payrol tape
Assumed you defined a server device "backup" in your server configuration
which refers to a directory the command below dumps the database payrol
to the file payrol.bkup in the specified directory:
dbctl -u dba dbstore payrol backup/payrol.bkup
To restore the database from the tape (after it has been purged)
the command below could be used:
dbctl -u dba dbrestore tape
The command below can be used to recover the database from the archive
file payrol.bkup in the directory the "backup" device refers to:
dbpurge -u dba payrol
dbctl -u dba dbrestore backup/payrol.bkup
The command below displays the backup header instead of restoring
the database:
dbctl -u dba dbrestore /info tape
The command below restores a previous backup to a new database:
dbctl -u dba dbrestore backup/payrol.bkup payrol-new
The backup files can be compressed during dbstore and uncompressed
during dbrestore.
Add the following to the [Devices] section of your eloqdb6.cfg file:
[devices]
zip = |gzip -c >/backup
unzip = |gzip -dc /backup
Please note: On HP-UX you may need to specify the path to gzip
(/usr/contrib/bin/gzip) if the global path does not include
the location of the gzip command.
When performing an backup to the "zip" destination this will cause
the backup file to be compressed. A dbrestore from the "unzip" source
is used to restore the compressed data.
dbctl -u dba dbstore payrol zip/payrol.bkup.gz
dbctl -u dba dbrestore unzip/payrol.bkup
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