vb.net 2d barcode generator Understanding the Need for Hints in C#

Printer EAN-13 Supplement 5 in C# Understanding the Need for Hints

Understanding the Need for Hints
Drawing EAN 13 In C#.NET
Using Barcode generator for .NET Control to generate, create GTIN - 13 image in .NET applications.
www.OnBarcode.com
GTIN - 13 Decoder In Visual C#
Using Barcode decoder for VS .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
SQL Server 2005 uses the cost-based optimizer (CBO) to dynamically generate query execution plans. The CBO probes several system-wide resource states and employs many complex algorithms to optimize and generate the best possible execution plan for a query. The optimization and query plan generation process is often costly, especially for complex queries. Once generated, query plans are cached in the SQL Server plan cache to avoid repeating the optimization task when the identical query is re-executed. You can view the query plans cached by SQL Server by querying the syscacheobjects table. For
Printing Barcode In C#
Using Barcode drawer for Visual Studio .NET Control to generate, create bar code image in VS .NET applications.
www.OnBarcode.com
Bar Code Scanner In Visual C#
Using Barcode recognizer for VS .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Part VII
Printing EAN / UCC - 13 In .NET
Using Barcode drawer for ASP.NET Control to generate, create EAN-13 image in ASP.NET applications.
www.OnBarcode.com
Creating EAN / UCC - 13 In VS .NET
Using Barcode generator for Visual Studio .NET Control to generate, create EAN-13 image in Visual Studio .NET applications.
www.OnBarcode.com
Performance Tuning and Troubleshooting
Making GTIN - 13 In VB.NET
Using Barcode maker for .NET framework Control to generate, create EAN 13 image in Visual Studio .NET applications.
www.OnBarcode.com
Painting EAN128 In Visual C#.NET
Using Barcode creation for .NET framework Control to generate, create GS1-128 image in .NET framework applications.
www.OnBarcode.com
example the following query can be used to list all the compiled plans in the instance of SQL Server:
Denso QR Bar Code Generator In Visual C#.NET
Using Barcode printer for Visual Studio .NET Control to generate, create Quick Response Code image in .NET applications.
www.OnBarcode.com
Drawing Barcode In C#.NET
Using Barcode generator for Visual Studio .NET Control to generate, create bar code image in .NET framework applications.
www.OnBarcode.com
SELECT * FROM sys.syscacheobjects WHERE cacheobjtype = 'Compiled Plan';
Encode UPC Code In C#
Using Barcode drawer for .NET Control to generate, create GS1 - 12 image in VS .NET applications.
www.OnBarcode.com
ISBN - 10 Maker In C#
Using Barcode drawer for Visual Studio .NET Control to generate, create ISBN - 10 image in .NET applications.
www.OnBarcode.com
Since the query plans are optimized for the specific data present in these tables, the SQL Server engine constantly monitors changes to the underlying tables and triggers a recompile of the query plan when it estimates that the data has changed significantly enough to justify a re-optimization. Once a query plan is recompiled, the old plan is discarded from the plan cache and replaced with the new plan. This targeted optimization and caching mechanism works perfectly well for most queries most of the time. However, it is occasionally (though rarely) necessary to force a particular query plan based on experience with the operation of the application, insights into idiosyncrasies in the application schema, or to force a better query execution plan than the one generated by the optimizer. This can be done very easily in SQL Server by using hints. Hints are directives that influence the behavior of the CBO but do not change the semantics of the query or the results in any way. During the optimization phase, the optimizer weighs the benefits among the various possible query plans to select the one that is best suited for the particular situation. Hints provided in the query bias this selection process. While query hints present a powerful method of manually controlling the behavior of the optimizer and give you control over how query plans are generated, they should be usedsparingly only as a last resort by experienced database administrators. The reason for this is simple: Once a query hint is specified, the optimizer is always biased toward choosing the query plan directed by the hint. This selection may be good for the situation at hand, but it may prevent the optimizer from choosing a possibly better plan at a later time when the shape of the underlying data or some other condition changes and the hint is no longer optimal.
Data Matrix ECC200 Generator In Visual Studio .NET
Using Barcode generation for .NET Control to generate, create ECC200 image in .NET framework applications.
www.OnBarcode.com
Decode GTIN - 128 In Visual Basic .NET
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Microsoft SQL Server 2005 Hints
Create UCC.EAN - 128 In Objective-C
Using Barcode generation for iPad Control to generate, create EAN / UCC - 13 image in iPad applications.
www.OnBarcode.com
UPC-A Printer In Java
Using Barcode maker for Java Control to generate, create UCC - 12 image in Java applications.
www.OnBarcode.com
In addition to the hints available in earlier SQL Server versions, SQL Server 2005 introduces many new hints, such as USE PLAN, FORCED PARAMETERIZATION, and so on. These hints can be used in all editions of SQL Server 2005.
Universal Product Code Version A Maker In Java
Using Barcode generator for BIRT reports Control to generate, create GTIN - 12 image in BIRT reports applications.
www.OnBarcode.com
Bar Code Drawer In None
Using Barcode creation for Font Control to generate, create bar code image in Font applications.
www.OnBarcode.com
33
Code39 Creation In Objective-C
Using Barcode creator for iPhone Control to generate, create Code 39 Extended image in iPhone applications.
www.OnBarcode.com
Paint Linear Barcode In .NET
Using Barcode generator for .NET Control to generate, create Linear 1D Barcode image in VS .NET applications.
www.OnBarcode.com
Tuning Queries Using Hints and Plan Guides
SQL Server 2005 classifies hints broadly into three categories: join hints, query hints, and table hints. The entire list of hints included in these categories is explained in the sections below.
Join Hints
Join hints are used to enforce a join strategy between the joined tables. When no join hint is specified (the default case for a majority of the queries), the optimizer automatically selects the join type that is best suited for the query. With SQL Server 2005, you can use join hints to force nested loop joins, hash joins, merge joins, and remote joins for SELECT, UPDATE, and DELETE statements. These hints are mutually exclusive, implying that only one of them can be specified for any query:
LOOP This hint specifies a nested loop join. In a nested loop join, every row in the inner table is checked using the join criteria to see whether the values of specified fields are equal to those in each corresponding row in the outer table. Nested loop joins are by far the most commonly used and are particularly well-suited for cases where a small number of rows from a table are joined to a large number of rows in another table. HASH This hint specifies a hash join. In a hash join, one table is reorganized as a hash table. The other table is scanned one row at a time, and the hash function is used to search for equalities. MERGE This hint specifies a merge join. In a merge join, each table is first sorted and then one row at a time from each table is compared with the corresponding row in the other table in descending order. REMOTE This hint specifies a remote join. A remote join is when at least one of the participating tables is remote. When this hint is specified, the join operation is performed on the site of the right table. This hint is useful when the left table is a local table (a table on the database where the query is executed) and the right table is a remote table (table on a remote database server). The REMOTE hint should be used only for inner joins when the left table has fewer rows than the right table.
Let s take a look at an example where a join hint is specified to force a merge join for a query executed against the AdventureWorks sample database:
SELECT EmployeeID, FirstName, LastName, EmailAddress, Phone FROM HumanResources.Employee e, Person.Contact c WHERE e.ContactID = c.ContactID OPTION (MERGE JOIN);
Copyright © OnBarcode.com . All rights reserved.