FIX: I/O requests that are generated by the checkpoint process may cause I/O bottlenecks if the I/O subsystem is not fast enough to sustain the IO requests in SQL Server 2005

This article describes the following about this hotfix release:

• The issues that are fixed by this hotfix package
• The prerequisites for applying the hotfix package
• Information about whether you must restart the computer after you apply the hotfix package
• Information about whether the hotfix package is replaced by any other hotfix package
• Information about whether you must make any registry changes after you apply the hotfix package
• The files that are contained in the hotfix package

In SQL Server 2005, the checkpoint process may generate periodic I/O spikes. If the I/O subsystem is not fast enough to sustain the I/O requests, I/O requests may cause I/O bottlenecks when the checkpoint process runs.

This problem occurs because the SQL Server checkpoint process posts as many I/O requests as possible when it determines that it must flush dirty buffers based on the recovery interval. This behavior is by default.

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must have Microsoft SQL Server 2005 Service Pack 1 (SP1) installed.

For more information about how to obtain SQL Server 2005 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:

Restart information

You do not have to restart the computer after you apply the hotfix.

Registry information

You do not have to change the registry.

Hotfix file information

This hotfix contains only those files that are required to correct the issues that this article lists. This hotfix may not contain of all the files that you must have to fully update a product to the latest build.

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

SQL Server 2005, 32-bit versions

SQL Server 2005, 64-bit version

SQL Server 2005, Itanium architecture version

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:

To use this hotfix to limit the number of checkpoint I/O requests per second, you must use the -kDecimalNumber startup parameter in SQL Server 2005. In this startup parameter, DecimalNumber represents the checkpoint speed in MB per second.

Note By default, the checkpoint process makes sure that SQL Server can recover databases within the recovery interval that you specify. If you enable this hotfix, the default behavior changes. Therefore, you may experience a long recovery time if you specify a very low value for the parameter. Additionally, backups may take a slightly longer time to finish because a checkpoint process that a backup initiates is also delayed. We recommend that you use the following methods to help eliminate an I/O bottleneck:

• Have enough hardware to sustain I/O requests that are posted by SQL Server.
• Perform sufficient application tuning.

If you do have to enable this hotfix, make sure that you perform enough testing before you apply this hotfix on production servers.

To configure SQL Server 2005 to use the -kDecimalNumber startup parameter, follow these steps

1. Start SQL Server Configuration Manager.
2. In SQL Server Configuration Manager, click SQL Server 2005 Services, right-click the instance of SQL Server 2005, and then click Properties. For example, right-click SQL Server (MSSQLSERVER).
3. In the SQL Server (MSSQLSERVER) Properties dialog box, click Advanced, and then click Startup Parameters.
4. At the end of the existing text, type ;-kDecimalNumber in the Value column, and then click OK.
   
   For example, if you want to throttle a checkpoint process to generate only 3 MB of I/O requests per second, use a startup parameter of –k3. When you do this, the checkpoint process calculates intervals automatically to keep the I/O requests within 3 MB per second.
5. Restart SQL Server for the parameters to take effect.

This hotfix is also included in the cumulative update package (build 3161) for SQL Server 2005 Service Pack 2. For more information, click the following article number to view the article in the Microsoft Knowledge Base: