Microsoft distributes Microsoft SQL Server 2008 R2 or Microsoft SQL Server 2012 fixes as one downloadable file. Because the fixes are cumulative, each new release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 or SQL Server 2012 fix release.
Symptoms
Consider the following scenario:
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You host a large database that has heaps in Microsoft SQL Server 2008 R2 or in Microsoft SQL Server 2012.
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You enable Read Committed Snapshot Isolation (RCSI) for the database.
In this scenario, you might experience low CPU spikes at a set interval (every five seconds), even when there is no user activity.Note This issue also occurs in Microsoft SQL Server 2005.
Cause
This issue occurs because heap pages are not synchronized with Page Free Space (PFS) pages. When RCSI is enabled, there might be some ghost records on the heap pages. When these ghost records are removed from the heap pages, the ghost bit is not removed from the PFS pages. This behavior causes a task that clears ghost records from PFS pages to execute repeatedly. This task will scan through the PFS pages every 5 seconds, triggering the issue that is described in the "Symptoms" section.
Resolution
Cumulative update information
SQL Server 2012
The fix for this issue was first released in Cumulative Update 1 for SQL Server 2012. For more information about this cumulative update package, click the following article number to view the article in the Microsoft Knowledge Base:
2679368 Cumulative update package 1 for SQL Server 2012Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2012 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2692828 The SQL Server 2012 builds that were released after SQL Server 2012 was released You must apply a SQL Server 2012 hotfix to an installation of SQL Server 2012.
SQL Server 2008 R2 Service Pack 1
The fix for this issue was first released in Cumulative Update 5 for SQL Server 2008 R2 Service Pack 1. For more information about how to obtain this cumulative update package, click the following article number to view the article in the Microsoft Knowledge Base:
2659694 Cumulative Update package 5 for SQL Server 2008 R2 Service Pack 1Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2567616 The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 1 was released
Cumulative update package 11 for SQL Server 2008 R2
The fix for this issue was first released in Cumulative Update 11. For more information about how to obtain this cumulative update package for SQL Server 2008 R2, click the following article number to view the article in the Microsoft Knowledge Base:
2633145 Cumulative update package 11 for SQL Server 2008 R2Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
981356 The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 was released
Workaround
To work around this issue, add a clustered index on tables that do not have a clustered index.
More Information
To verify that you are experiencing the same issue that is described in the "Symptoms" section, enable trace flag 661 to disable the cleanup of ghost records. If the low CPU spike goes away, then you are experiencing the same issue.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
