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. The 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 set a larger value for this variable.
MySQL Enterprise.
Subscribers to the MySQL Enterprise Monitor receive advice
on dynamically configuring the
max_connections
variable
— avoiding failed connection attempts. For more
information, see http://www.mysql.com/products/enterprise/advisors.html.
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
SHOW PROCESSLIST
to diagnose
problems even if the maximum number of unprivileged clients
are connected. See Section 12.4.5.30, “SHOW PROCESSLIST
Syntax”.
The maximum number of connections MySQL can support depends on the quality of the thread library on a given platform, the amount of RAM available, how much RAM is used for each connection, the workload from each connection, and the desired response time. Linux or Solaris should be able to support at 500–1000 simultaneous connections routinely and as many as 10,000 connections if you have many gigabytes of RAM available and the workload from each is low or the response time target undemanding. Windows is limited to (open tables × 2 + open connections) < 2048 due to the Posix compatibility layer used on that platform.
Increasing open-files-limit
may
be necessary. Also see Section 2.13.1.4, “Linux Post-Installation Notes”,
for how to raise the operating system limit on how many
handles can be used by MySQL.
User Comments
Detect "Too many connections" error and show alternate web page
<?php
$link = mysql_connect("localhost", "mysql_user", "mysql_password");
if (mysql_errno() == 1203) {
// 1203 == ER_TOO_MANY_USER_CONNECTIONS (mysqld_error.h)
header("Location: http://your.site.com/alternate_page.php");
exit;
}
?>
<?
ini_set('display_errors', '0');
$link = mysql_connect("localhost", "user", "pass");
if (mysql_errno() == 1040 OR mysql_errno() == 1203) {
define("DB_HOST", "some_ip:3306");//remote
define("DB_NAME", "db"); //database_name
define("DB_USER", "user"); //database user name
define("DB_PASSWORD","pass"); //database (user) password
}
else
{
define("DB_HOST", "localhost");
define("DB_NAME", "db_name2"); //database_name
define("DB_USER", "user"); //database user name
define("DB_PASSWORD","pass"); //database (user) password
}
ini_set('display_errors', '1');
//by feha at www.vision.to
?>
You can increase this value in main config file (e.g., /etc/my.cnf) using this syntax:
[mysqld]
set-variable=max_connections=250
A note por PHP developers. You can find this error if your scripts open persistent connections, wich aren't closed even if the script terminates. Use mysql_connect() instead of mysql_pconnect() unless you have a good reason. In particular, check this setting in third-party scripts (such as osCommerce).
Server administrators can disable persistent connections for PHP scripts in php.ini file:
[MySQL]
; Allow or prevent persistent links.
mysql.allow_persistent=Off
Scripts won't fail, they'll just use non-persistent connections silently.
Another symptom for PHP users, the "max_connections" error being returned to the browsers and the "show processlist" filling up with sleeping threads: This can sometimes be alleviated by using the PHP .htaccess option to lower the connect timeout from the default 60 seconds.
php_value mysql.connect_timeout 20
The osCommerce setting mentioned by ?varo is in the catalog/includes/configure.php file:
define('USE_PCONNECT', 'false'); // use persistent connections?
It defaults to true, so mysql_pconnect() is used, and you get the error message "Warning: mysql_pconnect(): Too many connections ..." Change to false for mysql_connect() to be used.
Please note that an instruction of the form
set-variable=max_connections=500
should be placed in the [mysqld] section. Otherwise MySQL will ignore it.
A lot of sites only suffer from this problem when Google or any other search bot is visiting. The best way to resolve this is to add the 'Crawl-delay' parameter in your robots.txt or to set it to a higher number of seconds.
I found that maxing out all available connections is not the only way to have this error. If your disk on your MySQL server is full, you can also get this error. Clearing up disk space will rid of the error.
Full explanation of what I've encountered here: http://www.microshell.com/database/mysql/mysql-too-many-connection-errors/
The following can also be used to change max_connections:
mysql> SET GLOBAL max_connections = 200;
However, this only lasts until the MySQL Server restarts.
On Solaris, you maybe limited to ulimits "open files".
i.e.
do ulimit -a
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
file size (blocks, -f) unlimited
open files (-n) 256
pipe size (512 bytes, -p) 10
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 29995
virtual memory (kbytes, -v) unlimited
Here "open files = 256" which is a very low setting.
At "open files = 1024" I was limited to 214 max connections.
In order the get the 500 + I wanted, I had to set "open files = 4096"
i.e. ulimit -n 4096
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