15 October 2013
15 October 2013

The ETL from Hell – Diagnosing Batch System Performance Issues

Too often, the batch systems that underlie a lot of database processing just grow without conscious design. When runs start to extend beyond their allotted time, and tuning no longer solves the problem, it is often discovered that batches are run in series, with draconian error handling. It is time to impose some rational design, and Nigel is a seasoned healer of batch processes.… Read more
19 April 2013
19 April 2013

Introduction to SQL Server Filtered Indexes

SQL Server filtered indexes can save space and improve performance if they are used properly. Under what circumstances can they be used? When are they most effective, and what sort of performance gain or space-saving is likely? How does a filtered index affect the choice of execution plan? Seth explores these questions with practical experiments… Read more
03 April 2013
03 April 2013

Managing SQL Server Statistics

Accurate statistics about the data held in tables are used to provide the best execution strategy for SQL queries. but if the statistics don't accurately reflect the current contents of the table you'll get a poorly-performing query. How do you find out if statistics are correct, and what can you do if the automatic update of statistics isn't right for the way a table is used? … Read more
05 March 2013
05 March 2013

Join Reordering and Bushy Plans

Normally, the query Optimiser won't consider 'bushy' plans, where both operands to a join operator could be intermediate results from other joins. This means that it won't produce good query plans for some types of query. Hints, by themselves won't do it. More powerful magic is required.… Read more
and 11 October 2012
and 11 October 2012

Tune Your Indexing Strategy with SQL Server DMVs

SQL Server Indexes need to be effective. It is wrong to have too few or too many. The ones you create must ensure that the workload reads the data quickly with a minimum of I/O. As well as a sound knowledge of the way that relational databases work, it helps to be familiar with the Dynamic Management Objects that are there to assist with your indexing strategy.… Read more
01 April 2011
01 April 2011

Improving Comparison Operators and Window Functions

It is dangerous to assume that your data is sound. SQL already has intrinsic ways to cope with missing, or unknown data in its comparison predicate operators, or Theta operators. Can SQL be more effective in the way it deals with data quality? Joe Celko describes how the SQL Standard could soon evolve to deal with data in ways that allow aggregation and windowing in cases where the data quality is less than perfect … Read more
14 March 2011
14 March 2011

The default trace in SQL Server – the power of performance and security auditing

Since the introduction of SQL Server 2005, there is a simple lightweight trace that is left running by default on every SQL Server. This provides some very valuable information for the DBA about the running server, but it isn't well-documented. Feodor reveals many of the secrets of this facility and shows how to get reports from it. … Read more
03 March 2011
03 March 2011

Lipoaspiration in your SQL Server Database

Once, when disk space was at a premium, DBAs fought hard to keep the size of their database down. Now there seems less motivation to 'fight the flab' of a database. Fabiano Amorim was watching television recently when the subject matter, cosmetic surgery, gave him the theme and inspiration for this guide to keeping your database fit and trim. … Read more
28 February 2011
28 February 2011

The EXCEPT and INTERSECT Operators in SQL Server

The UNION, EXCEPT and INTERSECT operators of SQL enable you to combine more than one SELECT statement to form a single result set. The UNION operator returns all rows. The INTERSECT operator returns all rows that are in both result sets. The EXCEPT operator returns the rows that are only in the first result set but not in the second. Simple? Rob Sheldon explains all, with plenty of examples… Read more
25 November 2010
25 November 2010

Index Selection and the Query Optimizer

While we all know that the Query Optimizer uses Indexes to produce better execution plans, we don't all know exactly which indexes will give the best results. Benjamin Nevarez has done the research, and in this sample from his upcoming book, "Inside the SQL Server Query Optimizer", he helps us to understand how the Query Optimizer selects indexes to improve execution plans.… Read more