(mysql.info) creating-many-tables

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(mysql.info) table-cache

(mysql.info) optimizing-database-structure

 
 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.
 

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(mysql.info) table-cache

(mysql.info) optimizing-database-structure