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SSC Clinic: Can Implementing "Optimize for Ad Hoc Queries" Boost Performance for the SQLServerCentral.com and Simple-Talk.Com SQL Servers?

With the introduction of the instance-level option “optimize for ad hoc workloads” in SQL Server 2008, DBAs have a tool to deal with a problem known as plan cache pollution, or plan cache bloat. It’s often caused when one-time use ad hoc queries are sent to SQL Server from Object-Relational Mapping (ORM) solutions, such as LINQ, NHibernate, or Entity Framework. The problem can prevent SQL Server from using its available memory optimally, potentially hurting performance.

External Article

SQL Server Prefetch and Query Performance

Prefetching can make a surprising difference to SQL Server query execution times where there is a high incidence of waiting for disk i/o operations, but the benefits come at a cost. Mostly, the Query Optimizer gets it right, but occasionally there are queries that would benefit from tuning.

External Article

A first look at SQL Server 2012 Availability Group Wait Statistics

If you are trouble-shooting an AlwaysOn Availability Group topology, a study of the wait statistics will give a pointer to many of the causes of problems. Although several wait types are documented, there is nothing like practical experiment to familiarize yourself with new wait stats, and Joe Sack demonstrates a way of testing the sort of waits generated by an availability group under various circumstances.

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ORDER BY alias

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Question of the Day

ORDER BY alias

There is a table tmp_tab: 

CREATE TABLE tmp_tab (
id int,
val int
);
INSERT INTO tmp_tab VALUES
(1, 1),
(2, NULL),
(3, 3),
(4, 4),
(5, 5);
You want to order the rows ids by the following expression: 
    ISNULL(val, id) + 1
Which of the following queries produces the expected ordering and why? (Select all correct)

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