If you have many MyISAM tables in the same database directory, open, close, and create operations are slow. 如果在同一数据库目录中有多个MyISAM表，则打开、关闭和创建操作会很慢。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. 如果在许多不同的表上执行SELECT语句，则当表缓存已满时会有一点开销，因为对于必须打开的每个表，都必须关闭另一个表。You can reduce this overhead by increasing the number of entries permitted in the table cache.您可以通过增加表缓存中允许的条目数来减少此开销。