SQL Indexing and Tuning

Preface: why is indexing is a development task

Separate what and how:

An SQL statement is a straight description what is needed without instructions as to how to get it done.

Developer must know a little bit about the database how run SQL to prevent performance problems

The most important information for indexing is how the application queries the data.

Anatomy of an Index (索引解剖)

注解

It is about the fundamental structure of an index

What is index
An index is a distinct structure in the database that is built using the create index statement. It requires its own disk space and holds a copy of the indexed table data. That means that an index is pure redundancy. Creating an index does not change the table data; it just creates a new data structure that refers to the table. A database index is, after all, very much like the index at the end of a book: it occupies its own space, it is highly redundant, and it refers to the actual information stored in a different place.
Why use index
  • An index makes the query fast

SQL database must process insert, delete and update statements immediately, keeping the index order without moving large amounts of data.

The database combines two data structures to meet the challenge: a doubly linked list and a search tree. These two structures explain most of the database's performance characteristics.

The Index Leaf Nodes

How to structure index