Lecture 9: Database efficiency

Introduction to Databases, Fall 2005
IT University of Copenhagen
Lecture 9: Database efficiency
November 7, 2005
Lecturer: Rasmus Pagh

• Database efficiency
• Indexing
• A little about schema tuning
• Database tuning cases

What you should remember from previously

In this lecture I will assume that you remember:
• That we characterized a DBMS as a system for providingefficient,
convenient, and safestorage of andmulti-useraccess to (possibly
massive) amounts ofpersistentdata.
• That each of the words in bold are important.
Here, “small” is relative to the best use of resources we could hope for:
• We don’t want the database to use 100 times more storage or
computation time than the best that the computer could be
programmed to do.

RDBMS efficiency is largely automatic

One of the reasons for the success of RDBMSs is that, to a large extent,
they are efficient “automatically”.
One of the great dividends of investing in an RDBMS is that you
don’t have to think too much about the computer’s inner life.
You’re the programmer and say what kinds of data you want. The
computer’s job is to fetch it and you don’t really care how.
Philip Greenspun in “SQL for Web Nerds”
This lecture is about some of the things that you, as a database
programmer, might have to do to help the RDBMS improve efficiency:
• Define suitable indexes.
• “Tune” the database schema.

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