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Query Store in SQL Server 2016

With the current version of the SQL Server, Microsoft is offering a new function with which you have the option of tracking changes in the performance of individual statements. We take a look at the details, the granularity of the data, constraints and use cases.

Who does not know the following situations: From now on an application or website becomes slower, after upgrading to SQL Server 2016 the server has become slower or you want to tune an application but don't know where to start. How do I find the queries that are bad or have deteriorated and the reason for them?

Before SQL Server 2016, it was possible to start an appropriately configured trace with the SQL Profiler, to use extended events or DMVs e.g. sys.dm_exec_query_stats, sys.dm_exec_cached_plans, but mostly only real-time data or aggregated data since the last restart deliver. Especially since this is usually only possible reactively, i.e. after a deterioration in performance has already become noticeable.

With the Query Store you now have the option to automatically collect and save SQL statements including execution plan and runtime statistics. The collected data is retained even after a restart and can be evaluated over different time intervals. In addition, if the access plan deteriorates, the best plan used can be selected using plan forcing. The Query Store is available in all SQL Server editions and is activated for each database.

The main differences to the query statistics with the DMVs are the availability of the data on statement level, the statement text is easily accessible, the measurement data is permanently retained and time intervals can be evaluated. In-memory queries are also covered.

The Query Store function can easily be activated and configured for a database in the SQL Server Management Studio. Alternatively also using T-SQL. The most important parameters are the Operation Mode and the Query Capture Mode. The Operation Mode determines whether data is collected (Read / Write) or only the collection is switched off and only the evaluation is possible (Read Only). The Query Capture Mode determines whether all statements (All) or only runtime-intensive, resource-intensive and frequently sent queries are to be collected. Here the Query Store decides which statements to save. This setting is certainly not for completeists who want to analyze all statements, but it is ideally suited for beginners and a more coarse analysis.

If the Query Store is activated, you can now analyze the performance measurements of a query with a specific execution plan, the history of the execution plans including all changes, or specify a specific execution plan used in the past for execution of a query. The SSMS offers four very useful views out-of-the-box:

  • Deteriorated execution plans
  • General resource consumption within a certain time interval
  • Top queries regarding runtime and resource consumption
  • Performance history of a specific query

The schema of the query store is documented in detail. There are numerous query store queries on the Internet for a wide variety of questions, but your own queries and evaluations, e.g. with Power BI, can be created quickly.

The advantages of the Query Store are, in addition to the simple activation, configuration and operation, the possibility of activating this function per database, so that one can analyze the workload especially of databases plagued by performance problems and take targeted tuning measures.

However, the Query Store also has a few restrictions. It is not available for the Master and TempDB. What seems bearable at first glance becomes a problem with queries that do not have an explicit Use command, since the Query Store only intercepts those queries whose sessions are explicitly connected to this database with Use. Queries from tempdb to other databases are also not recorded. The configuration is also associated with manual effort, the possibility of an instance-wide standard configuration is not given. You should also keep an eye on the storage space consumption of the query store. The data is stored in the primary filegroup of the respective database, which cannot be changed. Therefore, one should find a balance between memory usage and a reasonable amount of historical data. Also, no context information about the query is saved, e.g. who executed the query? Which program / server or stored procedure? By focusing on the SQL statement, performance tuning is clearly in the foreground.

Despite these limitations, the Query Store is a nice tool for performance tuning with SQL Server, with its help you can quickly and easily identify and correct deterioration in the execution plan and it is very suitable for workload analysis.