rzuć okiem na porównania silników mysql ->
http://dev.mysql.com/doc/refman/5.1/en/storage-engines.htmlzainteresuje Cię na pewno tabelka (Storage limits)
Poza tym w manualu znajdziesz też taki wpis:
Cytat
Scalability and Limits:
Support for large databases. We use MySQL Server with databases that contain 50 million records. We also know of users who use MySQL Server with 200,000 tables and about 5,000,000,000 rows.
Support for up to 64 indexes per table (32 before MySQL 4.1.2). Each index may consist of 1 to 16 columns or parts of columns. The maximum index width is 1000 bytes (767 for InnoDB); before MySQL 4.1.2, the limit is 500 bytes. An index may use a prefix of a column for CHAR, VARCHAR, BLOB, or TEXT column types.