Understanding Isolation Levels in .NET

Drawer PDF 417 in .NET Understanding Isolation Levels

Understanding Isolation Levels
PDF-417 2d Barcode Generation In .NET Framework
Using Barcode printer for VS .NET Control to generate, create PDF 417 image in .NET framework applications.
www.OnBarcode.com
PDF417 Reader In .NET Framework
Using Barcode recognizer for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
SQL Server 2005 specifies five different isolation levels that affect the way transactions are handled and the duration of locks. Table 15-2 describes each of these isolation levels.
Bar Code Generation In .NET
Using Barcode maker for VS .NET Control to generate, create bar code image in VS .NET applications.
www.OnBarcode.com
Barcode Scanner In VS .NET
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
15
PDF-417 2d Barcode Printer In Visual C#.NET
Using Barcode printer for Visual Studio .NET Control to generate, create PDF 417 image in VS .NET applications.
www.OnBarcode.com
PDF 417 Generator In Visual Studio .NET
Using Barcode maker for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
www.OnBarcode.com
Monitoring and Troubleshooting SQL Server Performance
Making PDF417 In VB.NET
Using Barcode drawer for .NET framework Control to generate, create PDF-417 2d barcode image in VS .NET applications.
www.OnBarcode.com
Encoding Bar Code In Visual Studio .NET
Using Barcode maker for VS .NET Control to generate, create bar code image in .NET framework applications.
www.OnBarcode.com
Table 15-2 SQL Server 2005 Isolation Levels
EAN 128 Encoder In .NET
Using Barcode generation for VS .NET Control to generate, create GS1 128 image in .NET applications.
www.OnBarcode.com
Encoding QR Code 2d Barcode In Visual Studio .NET
Using Barcode generation for VS .NET Control to generate, create QR Code 2d barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Isolation level READ UNCOMMITTED READ COMMITTED
Code39 Encoder In .NET Framework
Using Barcode drawer for .NET Control to generate, create Code 39 Full ASCII image in VS .NET applications.
www.OnBarcode.com
Identcode Generation In .NET Framework
Using Barcode generation for VS .NET Control to generate, create Identcode image in VS .NET applications.
www.OnBarcode.com
Description This isolation level lets other connections read data that has not yet been committed. This isolation level prevents other connections from reading data that is being modified until the transaction has been committed. Connection 1 is not allowed to read data that has been modified but not yet committed by Connection 2. Additionally, no other connection is allowed to modify any data that has been read by Connection 1 until the transaction completes. This causes shared locks to be placed on all data that is read, and the locks are held until the transaction completes. This isolation level places all of the restrictions as REPEATABLE READ and prevents new rows from being inserted within the keyset range that is locked by a transaction. Commonly known as readers do not block writers and writers do not block readers, this isolation level uses row versioning and ensures that a read operation will return the image of the data as it existed prior to the start of a modification.
Encode Code 3/9 In Java
Using Barcode generator for Android Control to generate, create ANSI/AIM Code 39 image in Android applications.
www.OnBarcode.com
DataMatrix Generator In None
Using Barcode generation for Word Control to generate, create Data Matrix image in Office Word applications.
www.OnBarcode.com
REPEATABLE READ
Recognizing Bar Code In .NET Framework
Using Barcode reader for .NET framework Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
QR Code 2d Barcode Creation In None
Using Barcode printer for Online Control to generate, create QR Code image in Online applications.
www.OnBarcode.com
READ SERIALIZABLE
Barcode Generator In Visual Studio .NET
Using Barcode printer for ASP.NET Control to generate, create bar code image in ASP.NET applications.
www.OnBarcode.com
EAN-13 Supplement 5 Decoder In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
SNAPSHOT
Paint Barcode In None
Using Barcode printer for Microsoft Excel Control to generate, create barcode image in Microsoft Excel applications.
www.OnBarcode.com
Recognizing Bar Code In VB.NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Understanding Blocking
Because read operations place shared locks on rows, pages, or tables, and update operations need to place exclusive locks on rows, pages, or tables, conflicts can occur between locks an exclusive lock cannot be acquired against a resource that has a shared lock. This condition is called blocking and is a normal operation in multiuser environments to ensure integrity of data and of query results. Any blocking occurring within an environment should be of a very short duration. Having processes blocked for an extended period of time generally defined as longer
Lesson 6: Resolving Blocking and Deadlocking Issues
than one second creates contention, lowers concurrency, and is generally manifested as performance problems within an application. To determine whether processes are being blocked and to identify the process that is creating the blocking, you would use the sys.dm_exec_requests DMV. If a value greater than 0 exists in the blocking_process_id column, the process is being blocked by the SPID logged in this column. You need to carefully monitor blocking issues because they are not actually error conditions. SQL Server is processing requests exactly as intended. However, a blocked process cannot complete until the process that is blocking it has finished and released all the competing locks.
Terminating Processes
In severe cases of blocking, you might need to forcibly terminate a process to allow other processes to complete. Termination should always be a last resort, but it is the only way to allow other processes to complete when they are being blocked by another process. The command to terminate a process is KILL spid, where spid is the session ID assigned to the blocking process. This command can be executed only by a member of the sysadmin fixed server role. When executed, this command immediately terminates a process. Any open transactions are rolled back, and an error is returned to the application.
Understanding Deadlocking
When a process is blocked, SQL Server still maintains a clear process execution order. After a process that is creating a block has released any competing locks, the blocked process will continue executing. However, it is possible to have a combination of blocks that can never be resolved. This situation is called a deadlock. A deadlock always requires at least two processes, and each of those processes must be making a modification to data. If Process 1 were to acquire an exclusive lock on a row while Process 2 acquired an exclusive lock on a different row, you don t have a problem. However, if Process 1 then attempted to acquire a shared lock on the row that is exclusively locked by Process 2, and Process 2 at the same time attempts to acquire a shared lock on the row that is exclusively locked by Process 1, an impossible scenario is created. Neither process can ever complete because each process relies on the other process completing first. Figure 15-22 illustrates this scenario.
Copyright © OnBarcode.com . All rights reserved.