To adjust a database for higher performance, it's crucial to know which indexes to keep and which to discard. If a database is mostly read and rarely updated, it might make sense to keep more indexes. Poor indexing is a major cause for slowdown in commercial systems. Careless system administrators often won't investigate how common queries are run—they will just index random fields they "feel" will help performance. Don't do this! Use "explain" tools to check your queries and add indexes only when it makes a difference.
