Query history is a crucial aspect of database management, as it allows administrators to track changes, debug issues, and optimize performance. In SQL Server, there are several ways to retrieve query history, each with its own strengths and limitations.
Understanding the Query Cache
SQL Server stores recently executed queries in the plan cache, which can be accessed using dynamic management views (DMVs). The sys.dm_exec_cached_plans DMV contains information about cached plans, while sys.dm_exec_sql_text provides the actual query text. To retrieve query history from the plan cache, you can use the following T-SQL query:
SELECT t.[text]
FROM sys.dm_exec_cached_plans AS p
CROSS APPLY sys.dm_exec_sql_text(p.plan_handle) AS t
WHERE t.[text] LIKE N'%something unique about your query%';
This query filters queries based on a specific string, allowing you to narrow down the results. However, keep in mind that the plan cache has limitations, such as:
- The cache is volatile and can be evicted by SQL Server at any time.
- The cache only stores queries that have been executed recently.
Using Query Statistics
To retrieve more detailed information about query execution, you can join the sys.dm_exec_cached_plans DMV with sys.dm_exec_query_stats. This allows you to access statistics such as last execution time:
SELECT t.[text], s.last_execution_time
FROM sys.dm_exec_cached_plans AS p
INNER JOIN sys.dm_exec_query_stats AS s
ON p.plan_handle = s.plan_handle
CROSS APPLY sys.dm_exec_sql_text(p.plan_handle) AS t
WHERE t.[text] LIKE N'%something unique about your query%'
ORDER BY s.last_execution_time DESC;
This query provides a more comprehensive view of query history, including execution times and frequencies.
Third-Party Tools
While the plan cache and query statistics provide valuable insights, they have limitations. For more extensive query history tracking, consider using third-party tools such as:
- ApexSQL Log: A commercial tool for reading transaction logs and retrieving query history.
- SQL Log Rescue: A free tool (limited to SQL Server 2000) for analyzing transaction logs.
These tools can help you retrieve query history that is not available through the plan cache or query statistics.
Profiler and Traces
For real-time monitoring and auditing, consider using SQL Server Profiler or tracing. These tools allow you to capture queries as they are executed, providing a more comprehensive view of database activity.
- SQL Server Profiler: A graphical tool for capturing and analyzing queries.
- Tracing: A server-side mechanism for capturing queries and storing them in a file for later analysis.
Conclusion
Retrieving query history in SQL Server requires a combination of understanding the plan cache, query statistics, and third-party tools. By leveraging these resources, you can gain valuable insights into database activity, optimize performance, and troubleshoot issues more effectively.