DBCC FREEPROCCACHE (Transact-SQL)

 

Updated: August 2, 2016

THIS TOPIC APPLIES TO:yesSQL Server (starting with 2008)noAzure SQL DatabaseyesAzure SQL Data Warehouse yesParallel Data Warehouse

Removes all elements from the plan cache, removes a specific plan from the plan cache by specifying a plan handle or SQL handle, or removes all cache entries associated with a specified resource pool.

NOTE: DBCC FREEPROCCACHE does not clear the execution statistics for natively compiled stored procedures. The procedure cache does not contain information about natively compiled stored procedures. Any execution statistics collected from procedure executions will appear in the execution statistics DMVs: sys.dm_exec_procedure_stats (Transact-SQL) and sys.dm_exec_query_plan (Transact-SQL).

Topic link icon Transact-SQL Syntax Conventions

-- Syntax for SQL Server  
  
DBCC FREEPROCCACHE [ ( { plan_handle | sql_handle | pool_name } ) ] [ WITH NO_INFOMSGS ]  

-- Syntax for Azure SQL Data Warehouse and Parallel Data Warehouse  
  
DBCC FREEPROCCACHE [ ( COMPUTE | ALL ) ] 
     [ WITH NO_INFOMSGS ]   
[;]  
  

( { plan_handle | sql_handle | pool_name } )
plan_handle uniquely identifies a query plan for a batch that has executed and whose plan resides in the plan cache. plan_handle is varbinary(64) and can be obtained from the following dynamic management objects:

sql_handle is the SQL handle of the batch to be cleared. sql_handle is varbinary(64) and can be obtained from the following dynamic management objects:

pool_name is the name of a Resource Governor resource pool. pool_name is sysname and can be obtained by querying the sys.dm_resource_governor_resource_pools dynamic management view.

To associate a Resource Governor workload group with a resource pool, query the sys.dm_resource_governor_workload_groups dynamic management view. For information about the workload group for a session, query the sys.dm_exec_sessions dynamic management view.

WITH NO_INFOMSGS
Suppresses all informational messages.

COMPUTE
Purge the query plan cache from each Compute node. This is the default value.

ALL
Purge the query plan cache from each Compute node and from the Control node.

Use DBCC FREEPROCCACHE to clear the plan cache carefully. Freeing the plan cache causes, for example, a stored procedure to be recompiled instead of reused from the cache. This can cause a sudden, temporary decrease in query performance. For each cleared cachestore in the plan cache, the SQL Server error log will contain the following informational message: "SQL Server has encountered %d occurrence(s) of cachestore flush for the '%s' cachestore (part of plan cache) due to 'DBCC FREEPROCCACHE' or 'DBCC FREESYSTEMCACHE' operations." This message is logged every five minutes as long as the cache is flushed within that time interval.

The following reconfigure operations also clear the procedure cache:

  • access check cache bucket count

  • access check cache quota

  • clr enabled

  • cost threshold for parallelism

  • cross db ownership chaining

  • index create memory

  • max degree of parallelism

  • max server memory

  • max text repl size

  • max worker threads

  • min memory per query

  • min server memory

  • query governor cost limit

  • query wait

  • remote query timeout

  • user options

When the WITH NO_INFOMSGS clause is not specified, DBCC FREEPROCCACHE returns:

"DBCC execution completed. If DBCC printed error messages, contact your system administrator."

Requires ALTER SERVER STATE permission on the server.

Multiple DBCC FREEPROCCACHE commands can be run concurrently.

In SQL Data Warehouse or Parallel Data Warehouse, clearing the query plan cache can cause a temporary decrease in query performance when queries are recompiled. DBCC FREEPROCCACHE (COMPUTE) only causes SQL Server to recompile queries when they are run on the Compute nodes. It does not cause SQL Data Warehouse or Parallel Data Warehouse to recompile the parallel query plan that is generated on the Control node.

DBCC FREEPROCCACHE can be cancelled during execution.

DBCC FREEPROCCACHE can not run within a transaction.

DBCC FREEPROCCAHCE is not supported in an EXPLAIN statement.

A new row is added to the sys.pdw_exec_requests system view when DBCC FREEPROCCACHE is run.

A. Clearing a query plan from the plan cache

The following example clears a query plan from the plan cache by specifying the query plan handle. To ensure the example query is in the plan cache, the query is first executed. The sys.dm_exec_cached_plans and sys.dm_exec_sql_text dynamic management views are queried to return the plan handle for the query. The plan handle value from the result set is then inserted into the DBCC FREEPROCACHE statement to remove only that plan from the plan cache.

USE AdventureWorks2012;  
GO  
SELECT * FROM Person.Address;  
GO  
SELECT plan_handle, st.text  
FROM sys.dm_exec_cached_plans   
CROSS APPLY sys.dm_exec_sql_text(plan_handle) AS st  
WHERE text LIKE N'SELECT * FROM Person.Address%';  
GO  

Here is the result set.

plan_handle text

-------------------------------------------------- -----------------------------

0x060006001ECA270EC0215D05000000000000000000000000 SELECT * FROM Person.Address;

(1 row(s) affected)

-- Remove the specific plan from the cache.  
DBCC FREEPROCCACHE (0x060006001ECA270EC0215D05000000000000000000000000);  
GO  

B. Clearing all plans from the plan cache

The following example clears all elements from the plan cache. The WITH NO_INFOMSGS clause is specified to prevent the information message from being displayed.

DBCC FREEPROCCACHE WITH NO_INFOMSGS;  

C. Clearing all cache entries associated with a resource pool

The following example clears all cache entries associated with a specified resource pool. The sys.dm_resource_governor_resource_pools view is first queried to obtain the value for pool_name.

SELECT * FROM sys.dm_resource_governor_resource_pools;  
GO  
DBCC FREEPROCCACHE ('default');  
GO  

D. DBCC FREEPROCCACHE Basic Syntax Examples

The following example removes all existing query plan caches from the Compute nodes. Although the context is set to UserDbSales, the Compute node query plan caches for all databases will will be removed. The WITH NO_INFOMSGS clause prevents informational messages from appearing in the results.

USE UserDbSales;  
DBCC FREEPROCCACHE (COMPUTE) WITH NO_INFOMSGS;  

The following example has the same results as the previous example, except that informational messages will show in the results.

USE UserDbSales;  
DBCC FREEPROCCACHE (COMPUTE);  

When informational messages are requested and the execution is successful, the query results will have one line per Compute node.

E. Granting Permission to run DBCC FREEPROCCACHE

The following example gives the login David permission to run DBCC FREEPROCCACHE.

GRANT ALTER SERVER STATE TO David;  

DBCC (Transact-SQL)
Resource Governor

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