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FIX: Data Collector job takes a long time to clear data from an MDW database in SQL Server 2008 or SQL Server 2008 R2

Article ID: 2584903 - View products that this article applies to.

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SYMPTOMS

Consider the following scenario:

A Management Data Warehouse (MDW) database has a snapshots.query_stats table that contains a large amount of data in Microsoft SQL Server 2008 or in Microsoft SQL Server 2008 R2.
You run the following Data Collector job to clear data from the MDW database.
mdw_purge_data_[<MDW database name>]

In this scenario, it takes a long time for the Data Collector job to clear data.

Notes

The Data Collector job calls the core.sp_purge_data stored procedure to clear data.
For more information about this issue in SQL Server 2008 R2, visit the following Microsoft website:
General information about this issue in SQL Server 2008 R2
(http://connect.microsoft.com/SQLServer/feedback/details/657148/management-data-warehouse-mdw-purge-job-proc-performance)

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CAUSE

This issue occurs because the mdw_purge_data job takes a long time to perform a batch-oriented clear operation if the snapshots.query_stats table contains a large amount of data.

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RESOLUTION

Service pack information

SQL Server 2008

To resolve this issue in SQL Server 2008, follow these steps:

Obtain the latest service pack for SQL Server 2008.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:
968382
(http://support.microsoft.com/kb/968382/ )
How to obtain the latest service pack for SQL Server 2008
For an existing MDW database, you must update it by running the Configure Management Data Warehouse Wizard after you install the latest service pack for SQL Server 2008.

SQL Server 2008 R2

To resolve this issue in SQL Server 2008 R2, follow these steps:

Obtain the latest service pack for SQL Server 2008 R2.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2527041
(http://support.microsoft.com/kb/2527041/ )
How to obtain the latest service pack for SQL Server 2008 R2
For an existing MDW database, you must update it by running the Configure Management Data Warehouse Wizard after you install the latest service pack for SQL Server 2008 R2

Update the sp_purge_orphaned_notable_query_text stored procedure as follows:

Existing procedure

-- Deleting TOP N orphaned rows in query plan table by joining info from temp table variable
-- This is done to speed up delete query. 
DELETE TOP (@delete_batch_size) snapshots.notable_query_plan 
FROM snapshots.notable_query_plan AS qp , #tmp_notable_query_plan AS tmp
WHERE tmp.[sql_handle] = qp.[sql_handle]

Updated procedure

-- Deleting TOP N orphaned rows in query text table by joining info from temp table
-- This is done to speed up delete query. 
DELETE TOP (@delete_batch_size) snapshots.notable_query_text 
FROM snapshots.notable_query_text AS qt, #tmp_notable_query_text AS tmp
WHERE tmp.[sql_handle] = qt.[sql_handle]

Note These changes are required to correct the text of the sp_purge_orphaned_notable_query_text stored procedure because the delete statement incorrectly references the snapshots.notable_query_plan table after you apply SQL Server 2008 R2 Service Pack 1.

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