Database Reference
In-Depth Information
Chapter
1
Introduction
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To understand how SQL optimizers decide what table and index scans
should be performed to process SQL statements as efficiently as possible
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To be able to quantify the work being done during these scans to enable
satisfactory index design
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Type and background of audience for whom the topic is written
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Initial thoughts on the major reasons for inadequate indexing
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Systematic index design.
ANOTHER TOPIC ABOUT SQL PERFORMANCE!
Relational databases have been around now for over 20 years, and that's precisely
how long performance problems have been around too—and yet here is
another
topic on the subject. It's true that this topic focuses on the index design aspects
of performance; however, some of the other topics consider this area to a greater
or lesser extent. But then a lot of these topics have been around for over 20 years,
and the problems still keep on coming. So perhaps there is a need for a topic that
goes beyond the usual boundaries and starts to think about why so many people
are still having so many problems.
It's certainly true that the world of relational database systems is a very
complex one—it has to be if one reflects on what really has to be done to satisfy
SQL statements. The irony is that the SQL is so beautifully simple to write; the
concept of tables and rows and columns is so easy to understand. Yet we could
be searching for huge amounts of information from vast sources of data held
all over the world—and we don't even need to know where it is or how it can
be found. Neither do we have to worry about how long it's going to take or
how much it's going to cost. It all seems like magic. Maybe that's part of the
problem—it's too easy; but then of course, it
should
be so easy.
We still recognize that problems will arise—and huge problems at that.
Stories abound of “simple” queries that might have been expected to take a
fraction of a second appear to be quite happy to take several minutes or even
longer. But then, we have all these topics, and they tell us how to code the query
