Most import decision by Database Administrator is that a query on development server, where only hundred or thousand of rows exists, can also perform flawless according to given benchmarks when we will deploy same query on production server, where number of rows could be in millions.One solution is to insert millions of rows in testing environment and then check execution plan. But it’s really painful. Thanks to SQL Server, which has provided a better solution, since SQL Server 2005. Yes, you can test a query that base table contains only dozen of rows but can act like they have million of rows (or as much as you want). Let’s try with a simple query at Adventure Works.
SELECT p.ProductID, p.Name, pm.Name AS ProductModel, pmx.CultureID,
FROM Production.Product AS p
INNER JOIN Production.ProductModel AS pm
ON p.ProductModelID = pm.ProductModelID
INNER JOIN Production.ProductModelProductDescriptionCulture AS pmx
ON pm.ProductModelID = pmx.ProductModelID
INNER JOIN Production.ProductDescription AS pd
ON pmx.ProductDescriptionID =pd.ProductDescriptionID
WHERE pm.Name = 'Road-150'
How many rows each table (in above query) contains, check with following query.
SELECT OBJECT_NAME(object_id),rows FROM sys.partitions
WHERE object_id IN
AND index_id = 1
On execution of first query, you can find that in execution plan, SQL Server Optimizer took number of rows estimate from its table statistics and its showing correct estimated and actual number of rows.
Now we will deceive SQL Server Optimizer for number of rows of 'Production.Product' table. Simple use following update statistics BUT with undocumented options i.e. ROWCOUNT and PAGECOUNT
UPDATE STATISTICS Production.Product WITH ROWCOUNT = 10000000, PAGECOUNT = 1000000
Execute our first SELECT query but with “DBCC FREEPROCCACHE” and it will show a different execution plan, as SQL Server Optimizer thought now number of rows are 10000000.
Now we have a better picture, that what will be the execution plan if number of rows are increased to 10000000 and it will be helpful to place new indexes and to take deceision like applying partition scheme.
To restore, actual number of rows, just rebuild all indexes on 'Production.Product' table.
ALTER INDEX ALLON Production.ProductDescription REBUILD
Note: Don’t use this method on production server.
Aasim Abdullah is working as SQL Server DBA with CureMD (www.curemd.com) based in NY, USA. He has been working with SQL Server since 2007 (Version 2005) and has used it in many projects as a developer, administrator, database designer. Aasim's primary interest is SQL Server performance tuning. If he finds the time, he like to sketch faces with graphite pencils.