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From:John G. Heim Date:June 1 2010 3:40pm
Subject:Temporary tables created on disk: 99%
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On my db server, mysql has 2 gigabytes for temporary tables and yet its 
creating 99% of temporary tables on disk.

According to mysqltuner, 99% of temporary tables are created on disk. I've 
confirmed this via the "show global status like 'created%'" command.  This 
is in spite of having the following in my my.cnf:

tmp_table_size = 2G
max_heap_table_size = 2G

I have confirmed these values are really being used via the "show variables 
like" command. So there's no typo in my my.cnf. Mysqltuner says "Temporary 
table size is already large - reduce result set size" but that is not a 
practical suggestion in that none of the programs using the databases on the 
server were written by me.  I have databases for spamassassin bayesian 
rules, horde3 imp (webmail) and moodle on the system. I am not about to try 
to modify their code.

I'm running mysql from debian stable (5.0.1). I've double and triple checked 
the documentation and it sure looks as if setting tmp_table_size  and 
max_heap_table_size  to be very large should eliminate this problem. But it 
doesn't seem to work. I just have to be missing something. But what? My 
complete my.cnf is below.

PS: I have another server that is serving only drupal and it too is creating 
a high percentage of temp tables on disk (75%).  I figure the same setting 
is missing and/or wrong on both servers.

#
# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
#
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

# This will be passed to all mysql clients
# It has been reported that passwords should be enclosed with ticks/quotes
# escpecially if they contain "#" chars...
# Remember to edit /etc/mysql/debian.cnf when changing the socket location.
[client]
port  = 3306
socket  = /var/run/mysqld/mysqld.sock

# Here is entries for some specific programs
# The following values assume you have at least 32M ram

# This was formally known as [safe_mysqld]. Both versions are currently 
parsed.
[mysqld_safe]
socket  = /var/run/mysqld/mysqld.sock
nice  = 0

[mysqld]
#
# * Basic Settings
#
user  = mysql
pid-file = /var/run/mysqld/mysqld.pid
socket  = /var/run/mysqld/mysqld.sock
port  = 3306
basedir  = /usr
datadir  = /srv/mysql
tmpdir  = /tmp
language = /usr/share/mysql/english
skip-external-locking
#
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
#bind-address  = 127.0.0.1
#
# * Fine Tuning
#
# Commonly used optimization parameters
#
tmp_table_size = 2G
max_heap_table_size = 2G
key_buffer  = 2G
max_allowed_packet = 16M
thread_stack  = 128K
thread_cache_size = 256
# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched
myisam-recover  = BACKUP
max_connections        = 256
table_cache            = 1024
thread_concurrency     = 16
open_files_limit = 8192
#
# * Query Cache Configuration
#
query_cache_limit       = 16M
query_cache_size        = 512M
#
# * Logging and Replication
#
# Both location gets rotated by the cronjob.
# Be aware that this log type is a performance killer.
#log  = /var/log/mysql/mysql.log
#
# Error logging goes to syslog. This is a Debian improvement :)
#
# Here you can see queries with especially long duration
# To see slow queries, use 'show processlist'
log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 2
log-queries-not-using-indexes
#
# The following can be used as easy to replay backup logs or for 
replication.
# note: if you are setting up a replication slave, see README.Debian about
#       other settings you may need to change.
#server-id  = 1
#log_bin   = /var/log/mysql/mysql-bin.log
expire_logs_days = 10
max_binlog_size         = 100M
#binlog_do_db  = include_database_name
#binlog_ignore_db = include_database_name
#
# * BerkeleyDB
#
# Using BerkeleyDB is now discouraged as its support will cease in 5.1.12.
skip-bdb
#
# * InnoDB
#
# InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.
# Read the manual for more InnoDB related options. There are many!
# You might want to disable InnoDB to shrink the mysqld process by circa 
100MB.
#skip-innodb
innodb_buffer_pool_size = 2G

#
# * Security Features
#
# Read the manual, too, if you want chroot!
# chroot = /var/lib/mysql/
#
# For generating SSL certificates I recommend the OpenSSL GUI "tinyca".
#
# ssl-ca=/etc/mysql/cacert.pem
# ssl-cert=/etc/mysql/server-cert.pem
# ssl-key=/etc/mysql/server-key.pem



[mysqldump]
quick
quote-names
max_allowed_packet = 16M

[mysql]
#no-auto-rehash # faster start of mysql but no tab completition

[isamchk]
key_buffer  = 16M

#
# * NDB Cluster
#
# See /usr/share/doc/mysql-server-*/README.Debian for more information.
#
# The following configuration is read by the NDB Data Nodes (ndbd processes)
# not from the NDB Management Nodes (ndb_mgmd processes).
#
# [MYSQL_CLUSTER]
# ndb-connectstring=127.0.0.1


#
# * IMPORTANT: Additional settings that can override those from this file!
#   The files must end with '.cnf', otherwise they'll be ignored.
#
!includedir /etc/mysql/conf.d/


Thread
Temporary tables created on disk: 99%John G. Heim1 Jun
  • Re: Temporary tables created on disk: 99%Rob Wultsch1 Jun