It is generally well known that indices help a lot to speed up database queries (especially SELECT but also UPDATE and DELETE). It is less known, that indices also have some disadvantages.
One of these disadvantages is, that indices require space in memory and on disk. An other disadvantage of indices is, that they slow down DML statements like INSERT and DELETE.

We often see at our customers that they do not realized this behaviour. Now I found the time to show the impact of (too) many indices graphically.

In the following test scenario we created a simple table:

Content

• Result set with temporary sequence
• Determination of optimal length of prefixed indexes
• Using MySQL keywords in table or columm names
• Missing Primary Key Index
• Problems while installing a MySQL 5.5 database
• InnoDB AUTO_INCREMENT at 2^nd position

Result set with temporary sequence