Большая БД, есть таблицы по 10-15млн записей.
/dev/sda6 /tmp 2GB
tmp_table_size=1024M
много join запросов

Пришлось уменьшить
connect_timeout=8
interactive_timeout=12
wait_timeout=12


Ложится сервер mysql

150620 15:29:30 [Note] /usr/sbin/mysqld: ready for connections.
Version: '5.1.61' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL)
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_0.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_5.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_0.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 15:53:54 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 15:53:56 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_0.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 15:53:56 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 15:54:05 [ERROR] /usr/sbin/mysqld: Table '/var/tmp/#sql_7c31_9' is marked as crashed and should be repaired
150620 15:54:05 [ERROR] /usr/sbin/mysqld: Sort aborted
150620 15:54:59 [ERROR] /usr/sbin/mysqld: Table '/var/tmp/#sql_7c31_5' is marked as crashed and should be repaired
150620 15:54:59 [ERROR] /usr/sbin/mysqld: Sort aborted
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_0.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_6.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_0.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_6.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_4.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Disk is full writing '/var/tmp/#sql_7c31_6.MYI' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
150620 17:42:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs
150620 17:52:20 [ERROR] /usr/sbin/mysqld: Retry in 60 secs. Message reprinted in 600 secs

max_connections=75
max_user_connections=60
озу 96гб