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dbrepl utility

» Usage | Notes | Examples | See also
 
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  The dbrepl utility is used to replicate committed database transactions from a master server to a slave server. This utility needs to be run with dba or operator privileges.

The dbrepl utility reads the master server config file to obtain the location and naming convention of forward-log files. It then contacts the slave server and obtains the most recently synchronized checkpoint on the slave server. With this information the master server forward-log files are searched to locate a synchronization point. dbrepl then submits any enqueued transactions from this point to the slave server.

Once the slave server is up to date, any subsequently committed transactions should be replicated close to real-time, subject to communication bandwidth. Replication should only place a minor load on the master and slave server once synchronization has been achieved.

As the dbrepl utility reads the master server forward-log files, it should run on the same system as the master server and requires read-only access rights to the forward-log files of the master server.

Usage

dbrepl [options] [slave_server_addr]

options:
 -help        - show usage (this list)
 -C cfg       - replication configuration file
 -D           - run dbrepl in background
 -P pid_file  - create pid file
 -c cfg       - master server configuration file
 -v           - verbose, display progress
 -u name      - user name (defaults to dba)
 -p pswd      - password
 -d flags     - debug flags
 -l logfile   - log file name (or console/syslog)
 -S           - synchronize on existing log, then exit
 -G           - process current log generation, then exit
 -b bps[k|m]  - limit bandwidth to bps [kilo|mega] bits per second
 -Z           - enable compression 
 -T timestamp - process until point in time (incl.)

timestamp formats:
 YYYY-MM-DD HH:MM:SS | MM/DD/YYYY HH:MM:SS | DD.MM.YYYY HH:MM:SS
 Any character may be used to separate date and time
 time is optional (defaults to 00:00:00)
The option -C may be used to specify a replication config file that defines replication parameters. In this case any additional arguments are optional and may be used to temporarily replace settings in the configuration file.
If the -C option is not specified any replication parameters and the slave server must be specified on the command line.

The slave_server_addr command line argument specifies the slave server host name or IP address and service name or port number, separated by a colon (e.g. 194.64.71.28:8202). The host name or IP address may be omitted and defaults to localhost (127.0.0.1).

The options are:

-help
The -help option displays a brief help text.

-c eloqdb.cfg
The -c option may be used to specify the master server config file. If not present, the default eloqdb.cfg config file is used.

-v
The -v option enables additional log output.

-u user
-p password
The -u and -p options may be used to specify the database user name and password when connecting to the slave server. Alternatively, the EQ_DBUSER (and/or the EQ_DBPASSWORD) environment variable may be used to specify the credentials. The user defaults to dba.
Please note that a database user with operator or dba capabilities is required.

-S
-G
-T timestamp
The options -S, -G and -T may be used limit replication scope to enqueued changes, the current log generation or a point in time.

-l logfile
The option -l may be used to specify a log file. The log files "console" and "syslog" are special and result in log output to stderr and syslog.

-b bps
The -b option may be used to limit the network bandwidth consumed by the replication.

-Z
If the -Z option is present, traffic to the slave is sent compressed. This will reduce the replication bandwidth but will use additional CPU resources. It depends on the network speed if this benefits replication performance.

-D
The option -D is used on HP-UX and Linux to run the dbrepl process in the background. This option is primarily intended for use by the start/stop script to manage dbrepl instances.

-P pidfile
The option -P is used to create a PID file. This option is primarily intended for use by the start/stop script to manage dbrepl instances.

-d flags
The -d option specifies debug flags and is normally not used.

The EQ_DBSERVER environment variable may be used to specify the slave server address. The EQ_DBUSER (and EQ_DBPASSWORD) environment variables may be used as an alternative to the -u and -p options (to help preventing passwords from being recorded and visible in shell history or server log files).

By default, dbrepl synchronizes all enqueued changes and then closely follows any on-going changes on the master server.

  • If the -S option is present, dbrepl exits once all enqueued changes are synchronized.
  • If the -G option is present, dbrepl exits if the volume generation changes (e.g. master server is restarted, on-line backup or "dbctl forwardlog restart" is run).
  • If the -T option is present, dbrepl exits after processing all enqueued changes up to (and including) a given checkpoint date and time. The time defaults to 00:00:00 if not specified explicitly. Date and time can be separated by space or other characters, shell quoting might be required.
The -b option may be used to limit the network bandwidth consumed by the replication. This throttling can be useful in case the network link between master and slave(s) is not dedicated to dbrepl and should not be saturated by the replication during high activity periods on the master. Note, however, that such throttling results in slave servers no longer being updated "as fast as possible".

The bandwidth limit is specified as bits, kilo bits (k suffix) or megabits (m suffix) per second. Any suffix must directly follow the value. For example: The options "-b 2m" or "-b 2048k" or "-b 2097152" each specify a limit of 2 megabits per second, which is equivalent to 256 kilobytes per second.

Notes

  • Beginning with Eloquence B.08.20 the dbrepl process may be started from the command line to override selected options, but is typically controlled by a platform specific init script on HP-UX and Linux (or run as Windows service) to also allow integrating with system boot and shutdown.

  • To temporarily stop synchronization of a slave server, it is sufficient to stop (or kill) the dbrepl utility. On the next start dbrepl will continue from the previous point.

  • Please note that volume file operations outside transaction context, like dbvolextend or write mode of dbrepack, dbfsck or dbcfix make subsequent use of dbrepl impossible until the slave server(s) have been re-synchronized from a new baseline backup of the volume files on the master server.

  • The exit codes issued by dbrepl are:

    0 - successful execution, graceful exit
    (will only be issued if the -S or -G command line option is used and dbrepl executed normally until the existing log or the current generation has been processed)

    1 - failure, typically requires manual intervention
    (for example, a configuration problem on the replication master or slave servers)

    2 - invalid or -help command line option
    (the command line usage was output)

    3 - connection problem
    (could not connect or lost the connection to the replication slave server)

    Exit code 3 may be used in a script to retry the dbrepl invocation. Preferably, repeated invocations should be appropriately delayed, for example by sleeping 60 seconds between two invocations.

Examples

The example below uses the configuration repl.cfg to specify the replication parameters. The command line argument -S causes dbrepl to exit once the slave server is in sync.
$ dbrepl -C repl.cfg -v -S
R1: processing forward-log file: /fwlog/fw-1-1
R1: found synchronization point with slave server
...
R1: processing forward-log file: /fwlog/fw-12-1
R1: slave server is up-to-date until 2006-04-18 18:54:17

See also

dbrepl utility (B.08.20 release notes)
Database replication (documentation)
dbrepl config file


 
 
 
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