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Starting from MySQL 4.0.2 one can limit certain resources per user.
So far, the only available method of limiting usage of MySQL
server resources has been setting the max_user_connections
startup variable to a non-zero value. But this method is strictly
global and does not allow for management of individual users, which
could be of particular interest to Internet Service Providers.
Therefore, management of three resources is introduced on the individual user level:
A user in the aforementioned context is a single entry in the
user
table, which is uniquely identified by its user
and host
columns.
All users are by default not limited in using the above resources,
unless the limits are granted to them. These limits can be granted
only via global GRANT (*.*)
, using this syntax:
GRANT ... WITH MAX_QUERIES_PER_HOUR N1 MAX_UPDATES_PER_HOUR N2 MAX_CONNECTIONS_PER_HOUR N3; |
One can specify any combination of the above resources.
N1
, N2
, and N3
are integers and represent counts per hour.
If a user reaches the limit on number of connections within one hour, no further connections will be accepted until that hour is up. Similarly, if the user reaches the limit on number of queries or updates, further queries or updates will be rejected until the hour is up. In all cases, an appropriate error message shall be issued.
Current usage values for a particular user can be flushed (set to zero)
by issuing a GRANT
statement with any of the above clauses,
including a GRANT
statement with the current values.
Also, current values for all users will be flushed if privileges are
reloaded (in the server or using mysqladmin reload
)
or if the FLUSH USER_RESOURCES
command is issued.
The feature is enabled as soon as a single user is granted with any
of the limiting GRANT
clauses.
As a prerequisite for enabling this feature, the user
table in
the mysql
database must contain the additional columns, as
defined in the table creation scripts mysql_install_db
and
mysql_install_db.sh
in `scripts' subdirectory.
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