DATABASE

SQL Server 2008 R2 : The Maintenance Plan Wizard (part 1)

5/12/2013 7:06:56 PM

The Maintenance Plan Wizard is a tool that is available in SSMS. It provides an automated means for creating the basic tasks needed to maintain a database. It does not include all the tasks available for use in a maintenance plan but is a great starting point that allows you to quickly generate the basic elements of a good plan.

You launch the Maintenance Plan Wizard by expanding the Management node in SSMS and then right-clicking Maintenance Plans and selecting Maintenance Plan Wizard. The Maintenance Plan Wizard is like most other Microsoft wizards in that it presents sequential dialog boxes that allow you to incrementally provide the information needed to create the wizard’s objective.

The Maintenance Plan Wizard first displays an introductory dialog box. When you click Next, it displays a dialog box (like the one shown in Figure 1) that allows you to specify the name and a description for your maintenance plan. You should choose a naming convention that will allow you to easily identify a maintenance plan and the type of maintenance it is performing. The name is displayed in the Object Explorer tree, and a good naming convention will make it easier to locate the plan you want.

Figure 1. Setting the Maintenance Plan Properties using the Maintenance Plan Wizard.


The Select Plan Properties screen also allows you to specify the schedule for the maintenance plan. This schedule will be tied to the corresponding scheduled job that is created when the Maintenance Plan Wizard completes. You will find that the scheduling dialog that appears when you click on the Change button is very flexible and consistent with other places in SQL Server where a schedule can be defined.

After you name the maintenance plan and specify the schedule, you can click Next. The dialog box that appears next allows you to select the maintenance tasks you would like to perform on the server. Figure 2 shows the Select Maintenance Tasks dialog, with the tasks that are available from the wizard. You can select more than one task for a given plan. As mentioned earlier, the tasks listed in the wizard are not all the tasks available in a maintenance plan.

Figure 2. Selecting maintenance tasks in the Maintenance Plan Wizard.


The dialog box that appears next, as shown in Figure 3, allows you to specify the order in which the tasks are executed. Obviously, the order of the tasks can be a critical factor and is dependent on the type of tasks you are running. You can click the Move Up and Move Down buttons to change the order of the tasks.

Figure 3. Selecting the order of the maintenance tasks in the Maintenance Plan Wizard.


The dialog boxes discussed so far are consistent for all the maintenance plans. The dialog boxes that follow are dependent on the tasks selected for the plan. Each task has a relevant set of properties that are displayed for entry in a subsequent dialog box. The following sections cover some of the common maintenance tasks and the wizard screens that relate to them.

Backing Up Databases

Backing up databases is the most basic element of a maintenance plan—and probably the most important part.For example, in the event of a disk drive failure, database backups can be used to restore the database data that was located on that drive.

The database backup options available via a maintenance plan include full, differential, and transaction log backups. The type of backup you select for a plan is heavily dependent on the type of environment you are maintaining and the type of database you are backing up. Databases that have very few changes may only need a nightly full backup and do not require transaction log or differential backups.

In most cases, it is a good idea to take a full backup of your system and user databases each night. Figure 4 shows the backup options the wizard displays for a full backup.

Figure 4. Full backup options in the Maintenance Plan Wizard.

To set the properties for a full backup, you need to first define the databases you want to back up. You select the databases by using the Databases drop-down at the top of the screen. This drop-down is unique in that it gives you a variety of radio button options rather than just a simple list. You can choose to back up all databases, all system databases, or all user databases, or you can select specific databases.

After you select the database(s) you want to back up, you must select a destination for the backup files. The destination includes the type of media (that is, tape or disk) and the file or files on that medium. The option Back Up Databases Across One or More Files allows you to specify one or more fixed files that the database backup will always be written to. With this option, you can choose to append each backup to the file(s) or overwrite the contents of the file(s) each time the backup is performed. If you choose to overwrite the backup each time, you have only the latest backup available for restoration. If you choose to append to the file, older backups are retained on this file, and the file continues to grow with each subsequent backup.

The preferred option for creating full backups with the wizard is the option Create a Backup File for Every Database. This option creates a separate file for each database in the maintenance plan. The backup file that is created has the database name as the first part of the filename, followed by _backup_ and then a time stamp that indicates when the backup was created. For example, a backup named AdventureWorks2008_backup_200608231402.bak would be a backup file created using this option for the AdventureWorks2008 database. Multiple versions of backups can be retained with this option, and the identification of the backup is simple because of the naming convention.

Caution

You should use the option Back Up Databases Across One or More Files with caution. The pitfall with overwriting the file with this option is that only one backup is available for restoration. When this option is used with the Append option, you can eat up all your disk space if the file is not cleaned up. In addition, if multiple databases are backed up with the plan, all these backups will be spread across the file or files specified for the destination. A separate backup for each database is not created with this option. This can lead to confusion and complicate the restoration process.

Generally speaking, you should steer clear of backing up the database to a single file or set of files. Instead, you should choose the option Create a Backup File for Every Database. This option has fewer pitfalls and requires little attendance.


When you use the Create a Backup File for Every Database option, you need to specify a folder for the database backups to be written to. You can use the default folder, or you can change it to a folder of your choice. It is a good practice to choose a folder on a drive that is different from the drive where your database files reside. Having backups on the same drive as your data could be a big problem if that drive fails and your only backups are on that drive. If you select the option Create a Sub-directory for Each Database, each database has a separate subfolder under the folder specified for the backup.

Caution

The main pitfall associated with the option Create a Backup File for Every Database is that many backup files can be created and are not automatically deleted by default. This point has been mentioned already, but it is a critical consideration. The good news is that you can now add the deletion of the older backups to the maintenance plan using the Maintenance Plan Wizard. To accomplish this, you need to select the Maintenance Cleanup task and provide the desired retention information that determines when the older backups are removed.


Another useful option on the Define Back Up Database screen is Verify Backup Integrity. If you select this option, SQL Server checks the integrity of the backup files that were written as part of the backup operation. Selecting this option extends the execution time for the backup plan but is generally a good idea to ensure that you have a viable backup for recovery. It is particularly useful when backups have been written across multiple files. Unfortunately, the backup task does not allow you to utilize the checksum options available with the SQL Server 2008 BACKUP command, but the basic VERIFY option suffices in most instances.

New to SQL Server 2008 is an option to define the compression for the database backup file. The Set Backup Compression drop-down at the bottom of the screen determines whether compression will be used. If the default for the server is set to compress backup or the specific option Compress Backup is selected, the backup file is created in a compressed format that will reduce the size of the backup file and save disk space. The trade-off when using compressed backups is that the creation of these backups takes additional CPU resources during their creation. However, the additional CPU processing time is typically offset by the faster I/O as a result of the reduced size of the backup file.

Note

In SQL Server 2008, compressed backups can only be performed in the Enterprise Edition. Beginning in SQL Server 2008 R2, compressed backups can be created in the Standard and all higher editions of SQL Server 2008 R2. Every edition of SQL Server 2008 and later can restore compressed backups, however.


Checking Database Integrity

The Define Database Check Integrity Task screen of the Maintenance Plan Wizard, shown in Figure 5, allows you to schedule the database consistency command DBCC CHECKDB, which checks the data pages for inconsistencies and is a good tool for ensuring that a database is healthy. The integrity checks can be made before each backup or on an independent schedule.

Figure 5. The Define Database Check Integrity Task screen of the Maintenance Plan Wizard.


The options available for checking database integrity via the wizard are limited.

Checking the Include Indexes check box causes integrity checks to be performed on the index pages as well. Checking the index pages for each table extends the amount of time the task runs, but it is the most thorough way to perform an integrity check. If problems are found, you can run the DBCC CHECKDB command manually with additional options to repair the problems.  In some cases, the problems cannot be fixed without the possibility of data loss. You should consider contacting Microsoft support if you receive consistency errors in a critical database.

Shrinking Databases

The Define Shrink Database Task page of the Maintenance Plan Wizard, shown in Figure 6, can be useful for keeping the size of your databases manageable. As its name implies, this task is used to reduce the overall size of a database. This task’s execution is essentially the equivalent to running the DBCC SHRINKDATABASE command, and it contains task options that mirror the options available with the DBCC command.

Figure 6. The Define Shrink Database Task page of the Maintenance Plan Wizard.


The setting Shrink Database When It Grows Beyond specifies the overall database size that must be exceeded for the shrink operation to occur. You set the size in megabytes, and it must be a whole number. If the database, including data and log files, is smaller than this size, the shrink operation does not occur.

The remaining options determine how the shrink operation runs when the shrink threshold is exceeded. The Amount of Free Space to Remain After Shrink option determines how much space is left in the database files after the shrink operation is finished. This is a target percentage and may not be feasible if the amount of disk space is limited. SQL Server does its best to achieve the target percentage, but it is not guaranteed. Generally, in environments where you have abundant disk space, it is best to leave at least 10% free after the operation so that the database can grow without the need for expanding the size of the database files.

The last settings on the screen determine how free space beyond the target percentage is handled. For example, let’s assume that a large number of rows were deleted from a database and the target free space percentage is set to 10%. The shrink operation is run and is able to shrink the database such that 40% is now free. You can choose to retain in the database files the 30% beyond the target that is free by selecting the Retain Freed Space in Database Files option. Choosing this option is the same as running the DBCC SHRINK DATABASE command with the NOTRUNCATE option. With this option, you do not see any changes to the size of the database files, and the free space on the disk remains unchanged.

The other option, Return Freed Space to Operating System, can reduce the size of the database files and return that space to the operating system. This option utilizes the TRUNCATEONLY option that comes with the DBCC SHRINK DATABASE command and is the option needed to free up disk space on a server.

Tip

Running the Shrink Database task for every database is not necessarily a good idea. With the Shrink Database task, the database is condensed so that the data is located on contiguous pages in the database data file(s). This involves the movement of pages from one part of the file to another. This movement can cause fragmentation in tables and indexes. The fragmentation can, in turn, cause performance problems and undo work that may have been done with other tasks, such as rebuilding the indexes.

The other problem with shrinking the database relates to the cost of expanding the database at a later time. For example, let’s say you have a database that has grown to 1GB. You shrink the database so that it is now only 800MB, but normal use of the database causes it to expand again. The expansion of the database files can be expensive and cause performance problems during the actual expansion, especially on high-volume production systems. The best solution is to purchase the appropriate amount of disk space and size the database so that database files do not need to expand frequently and the shrink operation is not needed. This is easier said than done, but it is the right answer nonetheless.

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