i am new to MySql.
We was assign to create new system by using MySql. At first, we just test on one module, and we get a pretty result. Then we proceed to other module, and more and more table need to add. One month later, when we test on the first module again, we found that it become slow..... and no changes on that module.
Are you indexed properly? What table types are you using? Is it slow inserting, updating or selecting? are you using fulltext indexing for searching raw text? you may want to look up EXPLAIN (to look at specific queries), ANALYZE (to look at table design) and BENCHMARK (to look at hardware performace).
Could you provide more details on the specific app, environment, etc??? There are some tweaks to make in the MySQL configuration file.