The speed of a slow SQL Query can almost always be improved. In SQL Server, the query optimizer determines the best way of executing the query, based on the evidence it has. The same query can be executed in many different ways as the data size increases, new indexes become available, or as the data distribution changes. If the appropriate index doesn't exist or can't be used, then SQL Server shrugs and does the best it can. Tony Davis explains how to find out what a query needs to perform w… Read more
It is always bad news if your SQL queries are having to use the SORT operator. It is worse news if you get a warning that sort operations are spilling onto TempDB. If you have a busy, slow TempDB, then the effect on performance can be awful. You should check your query plans to try to eliminate SORTs and never leave a SORT warning unheeded. Fabiano Amorim shows the range of ways of getting information on what is going on with a query that is doing a SORT and when requests are made for memory.… Read more
When you're developing database applications, it pays to check for index scans in the SQL Server query plan cache. Once you've identified the queries, what next? Dennes Torres gives some preliminary guidelines on how to find out why these index scans are being chosen for these queries and how to make the queries run faster and more efficiently.… Read more
When SQL Server 2014 was released, it included Hekaton, Microsoft's much talked about memory-optimized engine that brings In-Memory OLTP into play. With memory-optimized tables 30 times faster than disk-based tables, higher performance is promised - but at what cost? Jonathan Watts looks at the features that have improved, and those that need careful consideration.… Read more
Performance tuning and optimization definitely have their place in minimizing SQL Server Licensing costs - by helping keep CPU utilization low. But it's important to remember that the fastest and most efficient query possible is the one that you never execute against your SQL Server. That might sound trite, but it's at the heart of caching - which is key to helping organizations save significant money on SQL Server licensing costs while simultaneously enabling better application performance and increased scalability. … Read more
As a coder, the more you know about the business, the better code you're going to write. The more you know about the language in which you code regularly, the better code you're going to write. Similarly, if you're tasked with writing code against a relational database engine, you're going to need to know more about that engine. If you can examine and understand execution plans, you can achieve better understanding of the database system and you will write better database code. Grant Fritchey shows you how.… Read more
Dwain Camps show that, depending on the size and characteristics of some hierarchical data, six different methods of traversal can each be the fastest at some point. He illustrates convincingly that It is dangerous to generalize from just one set of test data, and it is foolish to assume that, just because SQL code looks neat, it will perform well.… Read more
One of the first things one needs to understand well about SQL Server is indexes, but somehow many of the basic questions don't often get asked or answered much on forums. Rob Sheldon answers some of these shy-making questions about SQL Server Indexes and indexing: the ones we somehow feel silly asking in public, and think twice about doing so.… Read more
Database administrators tend to rely more on science than intuition, and may therefore seem exasperatingly cautious to other IT people. A relational database is a complex machine, however, that is asked to deal with intricate problems. When things go wrong, it usually takes knowledge, deduction and a systematic approach to track down the root core of problems and to determine the best fix.… Read more
Imagine it. You've been asked to fix a dire performance problem with a SQL Server database. You find a severe case of 'Cache Bloat' due to ad-hoc queries, but you can't fix the code itself. What should you do? Specify forced parameterization? Perhaps a better idea would be to use guide plans.… Read more
When a SQL Server instance deadlocks, it can be anything from minor irritation to something far more severe. In this article, Gail Shaw looks at how you can identify common types of deadlock, the difference between a deadlock and severe blocking, and how to avoid and fix the most common deadlock types.… Read more
Alex Kuznetsov describes the agile principles, techniques and tools that allowed his development team to make frequent database refactoring a reality, without disrupting users. He explains how this allowed his team to apply an iterative, evolutionary approach to the design and development of their databases, as well as applications.… Read more
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
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
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
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
The performance of 'extract, transform, load' (ETL) processes for large quantities of data can always be improved by objective testing and experiment with alternative techniques. The cause of poor performance can sometimes be surprising.… Read more
If you need to optimise SQL Server performance, it pays to understand SQL Server Statistics. Grant Fritchey answers the 18 most frequently-asked questions about SQL Server Statistics: the ones we somehow feel silly asking in public, and think twice about doing so.… Read more
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
There are seven common antipatterns in TSQL coding that make code perform badly, and three good habits which will generally ensure that your code runs fast. If you learn nothing else from this list of great advice from Grant, just keep in mind that you should 'write for the optimizer'.… Read more
