7.4.9. Drawbacks to Creating Many Tables in the Same Database
If you have many
MyISAM tables in the same
database directory, open, close, and create operations are slow.
If you execute
SELECT statements on many
different tables, there is a little overhead when the table
cache is full, because for every table that has to be opened,
another must be closed. You can reduce this overhead by making
the table cache larger.