If you get a
Too many connections error
when you try to connect to the mysqld
server, this means that all available connections are in use
by other clients.
The number of connections allowed is controlled by the
max_connections system variable. Beginning
with MySQL 5.1.15, its default value is 151 to improve
performance when MySQL is used with the Apache Web server.
(Previously, the default was 100.) If you need to support more
connections, you should restart mysqld with
a larger value for this variable.
Subscribers to the MySQL Network Monitoring and Advisory
Service receive advice on dynamically configuring the
max_connections variable — avoiding
failed connection attempts. For more information see,
mysqld actually allows
max_connections+1 clients to connect. The
extra connection is reserved for use by accounts that have the
SUPER privilege. By granting the
SUPER privilege to administrators and not
to normal users (who should not need it), an administrator can
connect to the server and use
PROCESSLIST to diagnose problems even if the maximum
number of unprivileged clients are connected. See
SHOW PROCESSLIST 構文」.
The maximum number of connections MySQL can support depends on the quality of the thread library on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing. Static Linux binaries provided by MySQL AB can support up to 4000 connections.