MySQL Server Administration - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 282

Database information
The Databases subpage is intended to quickly get privileges information for each
database. Optionally, it can also be used to obtain global statistics on these databases,
without having to click on each database in the navigation panel. When we enter the
Databases subpage, we see the list of existing databases.
We also see an Enable Statistics link. By default, statistics are not enabled because
computing the size of data and indexes for all the tables in all the databases may cost
valuable MySQL server resources.
Enabling statistics
If we click this Enable Statistics link, a modified page appears. For each database, we
get the default collation for tables in this database, along with the number of tables
and the total number of rows for all tables. Next, information about the space used
by the data portion of the tables is given, followed by the space taken by all indexes
and total space for all tables. Finally, the space that could be reclaimed by optimizing
some tables in this database is presented under Overhead .