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  SQL Server Tips by Robin Schumacher

Rewrite and Benchmark

When the SQL is valid, the objects are in order, and object-based resolutions have been investigated, it is time to begin trying different code combinations in hopes of improving the query’s performance. This is where SQL tuning becomes an art.

Using hints, changing subqueries to joins, switching UNION’s to UNION ALL’s can become time consuming but rewarding as tuning becomes easier.

Once the DBA has assembled a suite of new SQL combinations for the existing query, it is time to actually send them through the database to see if anything is being accomplished. When performing these informal benchmarks, it is important to do them correctly.

For example, each query should not just be executed one time and the measurements recorded. First time executions typically take longer than subsequent tries due to parse activity and data being read in the first time from disk. At a minimum, each new query should be sent through three to four times with the high and low readings thrown out.


The above book excerpt is from:

High-Performance SQL Server DBA
Tuning & Optimization Secrets

ISBN: 0-9761573-6-5
Robin Schumacher

 http://www.rampant-books.com/book_2005_2_sql_server_dba.htm  

 

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