MySQL Basics Part 3 – Your my.cnf or my.ini file


Many novice MySQL DBAs peek at their option files with some trepidation. Many experienced members of their brethren view the files as incantations from some Harry Potter-ish dark art. These files are fairly simple to read and are there to help DBAs. The option or configuration files exist to keep you from having to type all your variations on the command line each time you restart your server.

At the bottom of this entry is the complete my.ini file from the MySQL instance on my laptop. It is nothing special, MySQL 5.5 on a Windows XP Oracle-standard Dell desktop, and I asked the Windows Installation Wizard that I wanted tables to support transactions.

This results in an option file that has fewer than two dozen lines to run the server. There are a good deal of comment lines that make the file larger. But the options set are relatively few. Such a small file is a good place to start learning how to configure a server and hopefully will not be imposing to a novice. So lets peek into the file.

The usual format is 'option=value' for each line.

The configuration file is usually divided into three sections (but you can add more) and the section name is in brackets, i.e. [client]. And yes, DBAs do often make mistakes by making a change in the wrong section, restarting the instance, and not realizing what they have done.

The first section is for the MySQL client program and in this example the section is not overwhelming:
[client]

port=3306

So when you fire up the MySQL command line client or other client application, it will automatically fill in ‘3306’ for the port number. So far, so good.,

Next is the [mysql] section:
[mysql]

mysql default-character-set=latin1

So a MySQL application will set the default character set to latin1. So why have two sections that both server applications? No reason. You could easily remove the [mysql] line and have the default-character-set line as part of the [client] section.

The majority of the commands fall under the [mysqld] section. The first three lines tell the MySQL daemon where to listen (port), where the MySQL files are located (basedir) , and where the data is stored (datadir). We will skip over things like SQL modes, cache sizing, and storage engine specific details right now.

[mysqld]
mysqld port=3306
basedir="C:/Program Files/MySQL/MySQL Server 5.5/"
datadir="C:/Documents and Settings/All Users/Application Data/MySQL/MySQL Server 5.5/Data/"
character-set-server=latin1
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
max_connections=341
.query_cache_size=9M
table_cache=700
tmp_table_size=16M
thread_cache_size=17

#*** MyISAM Specific options
myisam_max_sort_file_size=100G
myisam_sort_buffer_size=8M
key_buffer_size=13M
read_buffer_size=64K
read_rnd_buffer_size=256K
sort_buffer_size=208K

#*** INNODB Specific options ***
innodb_additional_mem_pool_size=2M
innodb_flush_log_at_trx_commit=1
innodb_log_buffer_size=1M
innodb_buffer_pool_size=22M
innodb_log_file_size=10M
innodb_thread_concurrency=10

So why have MyIsam configured if I am only using InnoDB?

The MySQL mysql database that holds all the account, grant, and other account details is still in MyISAM format. Do not change them to InnoDB or other storage engine.

So if I move the basedir and the datadir to different disks, will I get better performance?
That will be covered later and the brief answer is yes. For those of you wanting to dig into this area, search for ‘George Trujillo MOCA’.

Your file is only a subset of the options. How can I see what setting my instance is using?

Use SHOW VARIABLES with the command line client or MySQL Workbench.

Example of SHOW VARIABLES

Example of SHOW VARIABLES


  • Next: Storage engine tuning basics.
  • For deeper reading: Option Files


The complete my.ini file

# MySQL Server Instance Configuration File
# ----------------------------------------------------------------------
# Generated by the MySQL Server Instance Configuration Wizard
#
#
# Installation Instructions
# ----------------------------------------------------------------------
#
# On Linux you can copy this file to /etc/my.cnf to set global options,
# mysql-data-dir/my.cnf to set server-specific options
# (@localstatedir@ for this installation) or to
# ~/.my.cnf to set user-specific options.
#
# On Windows you should keep this file in the installation directory
# of your server (e.g. C:\Program Files\MySQL\MySQL Server X.Y). To
# make sure the server reads the config file use the startup option
# "--defaults-file".
#
# To run run the server from the command line, execute this in a
# command line shell, e.g.
# mysqld --defaults-file="C:\Program Files\MySQL\MySQL Server X.Y\my.ini"
#
# To install the server as a Windows service manually, execute this in a
# command line shell, e.g.
# mysqld --install MySQLXY --defaults-file="C:\Program Files\MySQL\MySQL Server X.Y\my.ini"
#
# And then execute this in a command line shell to start the server, e.g.
# net start MySQLXY
#
#
# Guildlines for editing this file
# ----------------------------------------------------------------------
#
# In this file, you can use all long options that the program supports.
# If you want to know the options a program supports, start the program
# with the "--help" option.
#
# More detailed information about the individual options can also be
# found in the manual.
#
#
# CLIENT SECTION
# ----------------------------------------------------------------------
#
# The following options will be read by MySQL client applications.
# Note that only client applications shipped by MySQL are guaranteed
# to read this section. If you want your own MySQL client program to
# honor these values, you need to specify it as an option during the
# MySQL client library initialization.
#
[client]

port=3306

[mysql]

default-character-set=latin1

# SERVER SECTION
# ----------------------------------------------------------------------
#
# The following options will be read by the MySQL Server. Make sure that
# you have installed the server correctly (see above) so it reads this
# file.
#
[mysqld]

# The TCP/IP Port the MySQL Server will listen on
port=3306

#Path to installation directory. All paths are usually resolved relative to this.
basedir="C:/Program Files/MySQL/MySQL Server 5.5/"

#Path to the database root
datadir="C:/Documents and Settings/All Users/Application Data/MySQL/MySQL Server 5.5/Data/"

# The default character set that will be used when a new schema or table is
# created and no character set is defined
character-set-server=latin1

# The default storage engine that will be used when create new tables when
default-storage-engine=INNODB

# Set the SQL mode to strict
sql-mode="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"

# The maximum amount of concurrent sessions the MySQL server will
# allow. One of these connections will be reserved for a user with
# SUPER privileges to allow the administrator to login even if the
# connection limit has been reached.
max_connections=341

# Query cache is used to cache SELECT results and later return them
# without actual executing the same query once again. Having the query
# cache enabled may result in significant speed improvements, if your
# have a lot of identical queries and rarely changing tables. See the
# "Qcache_lowmem_prunes" status variable to check if the current value
# is high enough for your load.
# Note: In case your tables change very often or if your queries are
# textually different every time, the query cache may result in a
# slowdown instead of a performance improvement.
query_cache_size=9M

# The number of open tables for all threads. Increasing this value
# increases the number of file descriptors that mysqld requires.
# Therefore you have to make sure to set the amount of open files
# allowed to at least 4096 in the variable "open-files-limit" in
# section [mysqld_safe]
table_cache=700

# Maximum size for internal (in-memory) temporary tables. If a table
# grows larger than this value, it is automatically converted to disk
# based table This limitation is for a single table. There can be many
# of them.
tmp_table_size=16M

# How many threads we should keep in a cache for reuse. When a client
# disconnects, the client's threads are put in the cache if there aren't
# more than thread_cache_size threads from before. This greatly reduces
# the amount of thread creations needed if you have a lot of new
# connections. (Normally this doesn't give a notable performance
# improvement if you have a good thread implementation.)
thread_cache_size=17

#*** MyISAM Specific options

# The maximum size of the temporary file MySQL is allowed to use while
# recreating the index (during REPAIR, ALTER TABLE or LOAD DATA INFILE.
# If the file-size would be bigger than this, the index will be created
# through the key cache (which is slower).
myisam_max_sort_file_size=100G

# If the temporary file used for fast index creation would be bigger
# than using the key cache by the amount specified here, then prefer the
# key cache method. This is mainly used to force long character keys in
# large tables to use the slower key cache method to create the index.
myisam_sort_buffer_size=8M

# Size of the Key Buffer, used to cache index blocks for MyISAM tables.
# Do not set it larger than 30% of your available memory, as some memory
# is also required by the OS to cache rows. Even if you're not using
# MyISAM tables, you should still set it to 8-64M as it will also be
# used for internal temporary disk tables.
key_buffer_size=13M

# Size of the buffer used for doing full table scans of MyISAM tables.
# Allocated per thread, if a full scan is needed.
read_buffer_size=64K
read_rnd_buffer_size=256K

# This buffer is allocated when MySQL needs to rebuild the index in
# REPAIR, OPTIMZE, ALTER table statements as well as in LOAD DATA INFILE
# into an empty table. It is allocated per thread so be careful with
# large settings.
sort_buffer_size=208K

#*** INNODB Specific options ***

# Use this option if you have a MySQL server with InnoDB support enabled
# but you do not plan to use it. This will save memory and disk space
# and speed up some things.
#skip-innodb

# Additional memory pool that is used by InnoDB to store metadata
# information. If InnoDB requires more memory for this purpose it will
# start to allocate it from the OS. As this is fast enough on most
# recent operating systems, you normally do not need to change this
# value. SHOW INNODB STATUS will display the current amount used.
innodb_additional_mem_pool_size=2M

# If set to 1, InnoDB will flush (fsync) the transaction logs to the
# disk at each commit, which offers full ACID behavior. If you are
# willing to compromise this safety, and you are running small
# transactions, you may set this to 0 or 2 to reduce disk I/O to the
# logs. Value 0 means that the log is only written to the log file and
# the log file flushed to disk approximately once per second. Value 2
# means the log is written to the log file at each commit, but the log
# file is only flushed to disk approximately once per second.
innodb_flush_log_at_trx_commit=1

# The size of the buffer InnoDB uses for buffering log data. As soon as
# it is full, InnoDB will have to flush it to disk. As it is flushed
# once per second anyway, it does not make sense to have it very large
# (even with long transactions).
innodb_log_buffer_size=1M

# InnoDB, unlike MyISAM, uses a buffer pool to cache both indexes and
# row data. The bigger you set this the less disk I/O is needed to
# access data in tables. On a dedicated database server you may set this
# parameter up to 80% of the machine physical memory size. Do not set it
# too large, though, because competition of the physical memory may
# cause paging in the operating system. Note that on 32bit systems you
# might be limited to 2-3.5G of user level memory per process, so do not
# set it too high.
innodb_buffer_pool_size=22M

# Size of each log file in a log group. You should set the combined size
# of log files to about 25%-100% of your buffer pool size to avoid
# unneeded buffer pool flush activity on log file overwrite. However,
# note that a larger logfile size will increase the time needed for the
# recovery process.
innodb_log_file_size=10M

# Number of threads allowed inside the InnoDB kernel. The optimal value
# depends highly on the application, hardware as well as the OS
# scheduler properties. A too high value may lead to thread thrashing.
innodb_thread_concurrency=10

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3 Comments

Filed under Basics, MySQL

3 responses to “MySQL Basics Part 3 – Your my.cnf or my.ini file

  1. Some notes from Lenz:

    Actually, the [client] option group is read by *all* MySQL client applications
    that are linked against the MySQL client library (libmysql), which also
    includes the “mysql” command line client. However, the command line client
    also has a dedicated section named [client], which you describe below.

    Please make sure to not confuse the [mysql] and [client] sections. It’s a bit
    counter-intuitive, please double check
    http://dev.mysql.com/doc/refman/5.5/en/option-files.html

    I suggest to add that MySQL assumes default values for all options that are not explicitly provided in the configuration file and that these are defined at compile time.

  2. thanks for this my.ini file i needed it for mysql command line client to work, as i had to put it in the \mySQL\mySQL Servier 5.0\ directory :)

  3. Sara AlSayed

    Than you very much for this usefull, easy MySQL tutorial. You have helped me a lot.

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