Chapter 7, Database Management

Table Of Contents

Database Management

Understanding Failure Resiliency

Database Files

Database Storage File

Database Transaction Log Files

Automatic Log Management

Miscellaneous Database Files

Disk Space Requirements

Handling Out of Disk Space Conditions

Backup and Recovery

Database Backup

Database Recovery

Database Restore

Changing Database Location

RDU Database Migration

Database Management

This chapter contains information on RDU database management and maintenance. The RDU database is the Broadband Access Center for Cable (BACC) central database. As with any database, it is essential that you, as the administrator, understand and be familiar with database backup and recovery procedures.

Understanding Failure Resiliency

The RDU database uses a technique known as write-ahead logging to protect against database corruption that could result from unforeseen problems, such as an application crash, system failure, or power outage.

Write-ahead logging involves writing a description of any database change to a log file prior to writing the change into the database files. This allows the repair of any incomplete database writes that can result from system failures.

The RDU server performs an automatic recovery each time it is started. During this recovery process, the log files are used to synchronize the data with the database files. Database changes that were written into the log, but not into the database, are written into the database during this automatic recovery.

In this way, write-ahead logging virtually guarantees that the database does not become corrupted when the RDU server crashes because the database is automatically repaired when the RDU server is restarted.

Write-ahead logging requires these conditions to work properly:

•The file system and physical storage must be set up so that they guarantee that the data is flushed to physical storage when requested. For example, a storage system with RAM-only write cache, which loses data during system failure, is not appropriate. However, a disk array with battery-backup write cache that guarantees that the data gets persisted, even in the event of a system failure, is acceptable.

•The file system must be set up with 8192 byte block size to match the RDU database block size. This is usually the default setting on Solaris unless explicitly adjusted.

Database Files

The RDU database stores data in binary files using the file system you have mounted on the partition containing the files. It is essential to choose and configure a file system so that it is not susceptible to long recovery times after system failures.

Database files are vital to the operation of the RDU. Therefore, take extra precaution measures to safeguard them against accidental removal or other manual manipulation. Follow standard system administration practices to safeguard these important files. For example, these files should always have permissions that allow only root user access. Additionally, it is a good practice to never log into your production system as a root user, but rather log in as a less privileged user and use the sudo command to execute tasks requiring root privileges.

Note Use the backup, restore, and recovery tools to perform corresponding tasks on the database. Previous Broadband Provisioning Registrar (BPR) releases allowed you to perform some of these tasks directly without using specific tools. Do not attempt to perform these tasks without using the tools. See the "Backup and Recovery" section for additional information on these tools.

Database Storage File

The RDU server stores its database in a file called bpr.db, which is found in the database directory. This directory is located in the <BACC_DATA>/rdu/db directory and is configured by specifying the BACC_DATA parameter during a component installation. See the "Changing Database Location" section for additional information on moving the database.

Note The database file is normally accessed in a random fashion. You should therefore, select a disk with the fastest seek time and rotational access latency to obtain the best database performance.

Database Transaction Log Files

The RDU server stores database transaction logs in 10 MB files that are stored in the database log directory. You configure this directory during installation by specifying the BACC_DBLOG parameter. The log directory is located in the <BACC_DBLOG>/rdu/dblog directory. See the "Changing Database Location" section for additional information on moving the transaction logs to a new directory.

Database log files are named in numeric sequence, starting at log.00000001, then log.00000002, and so on.

Note The disk on which transaction logs are stored is usually accessed in a sequential manner, with data being appended to the log files. Select a disk that can efficiently handle this access pattern to achieve the best database performance.

Automatic Log Management

Database transaction logs files are used to store transaction data until that data is completely written into the database. After that, the transaction log data becomes redundant and, because the RDU server database manages transaction log files automatically, the files are then automatically removed from the system. Under normal circumstances there should be only a few log files in the database transaction log directory. Over time, you will notice that older transaction logs disappear and newer ones are created.

Note Database transaction logs are an integral part of the database. Manual deletion of transaction log files may result in database corruption.

Miscellaneous Database Files

The database directory contains additional files that are essential to database operation. These files, in addition to the bpr.db file, are found in the <BACC_DATA>/rdu/db directory and are copied as part of the database backup:

•DB_VERSION—Identifies the physical and logical version of the database and is used internally by the RDU.

•history.log—Used to log activity about essential database management tasks, such as automatic log file deletion, backup, recovery, and restore operations. In addition to providing useful historical information for the administrator, this log file is essential to RDU database operation.

Disk Space Requirements

The size of a fully populated database depends on a number of factors. The main factors are the number of device objects managed by the RDU and the number of custom properties stored on each object. The approximate estimates for disk space required on each partition are:

•BACC_DATA, approximately 3 to 5 KB per device object

•BACC_DBLOG, at least 500 MB

Caution These numbers are provided as a guideline only and do not eliminate the need for normal system monitoring.

You can use the disk_monitor.sh command to monitor available disk space and alert the administrator. See the "Using the disk_monitor.sh Tool to Monitor Available Disk Space" section on page 12-51 for additional information.

Handling Out of Disk Space Conditions

When the RDU server runs out of disk space, it generates an alert through the syslog facility and the RDU log. The RDU server then tries to restart automatically. When attempting to restart, the RDU server may again encounter the out of disk space error and attempt to restart again.

The RDU server continues trying to restart until free disk space becomes available. Once you free up some disk space on the disk that is running into a limit, the next time the RDU restarts it will succeed.

If your database grows in size beyond the capacity of the current disk partition, then you should move the database to a new disk/partition. For information on how to do this, see the "Changing Database Location" section.

Note It is a good practice, to monitor disk space utilization to prevent failure. See the "Using the disk_monitor.sh Tool to Monitor Available Disk Space" section on page 12-51 for additional information.

Backup and Recovery

The RDU server supports a highly efficient backup process that can be performed without stopping the server or suspending any of its activities. Database backup and recovery involves these stages:

•Backup—Takes a snapshot of the RDU database from a live server.

•Recovery—Prepares the database snapshot for re-use.

•Restore—Copies the recovered database snapshot to the RDU server.

Automated tools are provided for each of these steps. You can use these tools in either interactive mode or silent mode, but you must have root privileges to use the tools.

Database Backup

Backup is the process of copying the database files into a backup directory. The files can then be compressed and placed on tape or other archive.

RDU database backup is highly efficient because it involves just copying files without interrupting server activity. However, because it involves accessing the RDU database disk, backup may adversely affect RDU performance. The opposite is also true. RDU activity happening during backup will adversely affect backup performance. Therefore, you should perform backups during off-peak hours.

Other than concurrent system activity, backup performance also depends on the underlying disk and file system performance. Essentially, backup will perform as fast as database files can be copied from source to target.

Use the backupDb.sh command, in the <BACC_DATA>/rdu/bin directory, to perform database backups:

•To use this command, you must provide the target directory where the backup files will be placed. This directory should be on a disk or partition that has available disk space equivalent to 120% of the current database file size.

•As illustrated in the following example, this command automatically creates a time stamped subdirectory, under the directory you specify and places the backups there.

Examples

Here is an example of using the backupDb.sh command:

backupDb.sh /var/backup

Where:

•/var/backup—identifies the database backup directory.

In this example, all backup database files are stored in a directory called /var/backup/rdu-backup- 09252002-130345. The last subdirectory (rdu-backup- 09252002-130345) is automatically created with a current timestamp.

Note The timestamped subdirectory format used is rdu-backup-MMddyyyy-HHmmss. In this example, the subdirectory would be rdu-backup-04272003-175430 meaning that the directory contains a backup that was started at 5:54:30 pm on April 27, 2003.

The backupDb.sh command also reports progress to the screen and logs its activity into history.log.

Note When using the backupDb.sh command, you can use a -help option to obtain usage information. You can also use another optional flag called -nosubdir to disable, if necessary, the automatic creation of the subdirectory.

Database Recovery

Database recovery is the process of restoring the database to a consistent state. Since backup is performed on a live RDU, the database can be changing while it is being copied. The database log files however, ensure that the database can be recovered to a consistent state.

Recovery is performed on a snapshot of a database. In other words, this task does not involve touching the database on the live RDU server. The recovery task can be performed either immediately following a backup or prior to restoring the database to the RDU server.

Note Cisco recommends that you perform database recovery immediately after each backup. This way, the backed up database can be more quickly restored in case of emergency.

The duration of database recovery depends on the number of database log files that were copied as part of the backup, which in turn depends on the level of RDU activity at the time of the backup. The more concurrent activity RDU experiences during the backup, the more transaction log files have to be copied as part of the backup and the longer is the recovery. Generally, recovering a database takes from 10 to 60 seconds per transaction log file.

Use the recoverDb.sh command, located in the <BACC_DATA>/rdu/bin directory, to perform recovery of the snapshot of a database. When you use this command, you must provide the location of the backup. This is also the directory in which the recovery will be performed.

Examples

Here is an example of using the recoverDb.sh command:

# recoverDb.sh /var/backup/rdu-backup-04272003-130345

In this example, the snapshot located in the /var/backup/rdu-backup-04272003-130345 directory will be recovered to a consistent state. The progress of the recovery operation will appear on screen and the activity will be recorded in the history.log file in the snapshot directory.

Note When using the recoverDb.sh command, you can use a -help option to obtain usage information on the command.

Database Restore

Restoring the database is the process of copying the previously recovered database snapshot to the database location used by the RDU server. Only a database that has been previously recovered can be restored.

Since restoring the database means replacing the current RDU database, it is very important that you first properly remove and archive the old database.

Note Never delete the database you are replacing. You might need a copy of an old database to simplify future system diagnostics.

Use the restoreDb.sh command located in the <BACC_DATA>/rdu/bin directory, to replace the current RDU database with another database. When using this command, you must specify an input directory. This directory must contain the recovered backup snapshot of the database to be restored to the RDU server.

Note Before running the restoreDb.sh utility, you must stop the RDU server.

Examples

Here is an example of running restoreDb.sh utility:

# restoreDb.sh /var/backup/rdu-backup-04272003-130345

In this example, the database found in the /var/backup/rdu-backup-042752003-130345 directory is restored to the RDU server.

Note When using the restoreDb.sh command, you can use a -help option to obtain usage information on the command.

You must restart the RDU after the restore operation is completed. The RDU log file will contain successful start up messages.

This command displays progress on screen and logs its activity into the history.log file.

Changing Database Location

You can move the database from one partition or disk to another on the same system. You might sometimes want to do this for administrative reasons. This process requires stopping the RDU server and the BPR agent.

The process of changing the database location involves changing one or two system parameters and copying the appropriate files to the new location. You can adjust one or both of the following parameters:

•BACC_DATA—This parameter is initially set during installation and points to a directory that is used to store the database, and many other important files, such as logs, configuration files, and so on.

•BACC_DBLOG—This parameter is initially set during installation and points to the directory that stores database transaction log files.

The values for the above parameters are recorded in a file called <BACC_DATA>/ bpr_definitions.sh. Any change to this file requires that you restart all BACC components running on the system.

To change the location of the database and transaction logs:

Step 1 Run the /etc/init.d/bprAgent stop command to stop the BACC agent.

Step 2 Make a backup copy of <BACC_DATA>/bpr_definitions.sh file.

Step 3 Edit the file and change BACC_DATA and/or BACC_DBLOG parameters to new directories.

Step 4 Save the file.

Step 5 Copy or move the directory structure and contents of the original BACC_DATA and/or BACC_DBLOG directories to new location(s). If you make a copy, make sure that all file and directory permissions are preserved.

Step 6 Run the /etc/init.d/bprAgent start command to start the BACC agent and all BACC components.

Step 7 Monitor the appropriate log files to ensure that all components have successfully started.

RDU Database Migration

All information concerning the migration of the RDU database is provided in the Cisco Broadband Access Center for Cable Installation Guide.