Free advice on your my.cnf

Today, while on IRC in #pentaho I came across a discussion and a published my.cnf. In this configuration I found some grossly incorrect values for per session buffers (see below).

It doesn’t take a MySQL expert to spot the issues, however there is plenty of bad information available on the Internet and developers not knowing MySQL well can easily be mislead. This has spurred me to create a program to rid the world of bad MySQL configuration. While my task is potential infinite, it will enable me to give back and hopefully do a small amount of good. You never know, saving those CPU cycles may save energy and help the planet.

Stay tuned for more details of my program.

sort_buffer_size = 6144K
myisam_sort_buffer_size = 1G
join_buffer_size = 1G
bulk_insert_buffer_size = 1G
read_buffer_size     = 6144K
read_rnd_buffer_size = 6144K
key_buffer_size		= 1024M
max_allowed_packet	= 32M
thread_stack		= 192K
thread_cache_size       = 256

query_cache_limit	= 512M
query_cache_size        = 512M


  1. says

    Truly a noble effort, especially as most of the information out there is either misleading or vague, or with a generally unhelpful “it depends on the situation”.

    Something that could lay out steps or outright analyze various “situations” based on tuning parameters and such would be amazing. Even as simple as an extended version of ( with more detailed performance implications and dependencies of any given variable. The closest thing I have found to what you’re suggesting is a “tuning primer script” by Matthew Montgomery, and probably worth taking a look at if you haven’t seen previously:

  2. ronald says

    Hi Erick,

    Yes, I know Matt well and while I’ve not looked at his script in several years I know people reference it.

    It’s difficult to tune a my.cnf without additional key information. This includes
    * System Memory, and available memory for MySQL
    * Database size/Growth
    * Storage Engines
    * SQL paths
    * Query volume

    It is however very easy to identify errors, omissions and outrageous values, and my first goal will be to at least identify these.

  3. says

    So for your critical review.

    Redhat 5.2 x64
    8G memory
    80DBs, Largest ~72Bytes x 32,000,000 rows
    All MyISAM with ~15 user connects and 2,000 SQL/s

    MySQL 5.1.37-SP1 Enterprise x64

    query_cache_limit = 16M # Don’t cache results that are larger than this number of bytes.
    query_cache_size = 512M # caching query Sizes > 128M may reduce performance
    query_cache_type = 1 # 1=ON – 2=OFF – 3=DEMAND
    thread_cache_size = 128 # How many threads the server should cache for reuse
    key_buffer = 32M # 64M for 1GB, 128M for 2GB, 256 for 4GB
    key_buffer_size = 4096M # Should be some less then 75% of total RAM
    join_buffer_size = 8M # 1M for 1GB, 2M for 2GB, 4M for 4GB
    max_allowed_packet = 32M # maximum size of one packet or any generated/intermediate string
    table_cache = 2048 # number of open tables for all threads
    sort_buffer_size = 1M # 1M for 1GB, 2M for 2GB, 4M for 4GB
    read_buffer_size = 1M # 1M for 1GB, 2M for 2GB, 4M for 4GB
    read_rnd_buffer_size = 768K # 768K for 1GB, 1536K for 2GB, 3072K for 4GB
    myisam_sort_buffer_size = 16M # 32M for 1GB, 64M for 2GB, 128 for 4GB
    table_definition_cache = 768 # number of table definitions that can be stored in the definition

  4. says

    I currently use Tuning Primer or Mysql Report to configure buffer sizes. But I agree that there is A LOT of misinformation out there and my.cnf configurations. As a general rule of thumb I use this formula to calculate mysql memory usage: memory=key_buffer+(sort_buffer_size+read_buffer_size)*max_connections

  5. Tejas Darji says


    My Drupal(CMS) site consume lots of memory.
    RAM : 1GB
    OS : CentOS release 5.2
    mysql : 5.0.45

    My current my.cnf file.

    # Example MySQL config file for very large systems.
    # This is for a large system with memory of 1G-2G where the system runs mainly
    # MySQL.
    # You can copy this file to
    # /etc/my.cnf to set global options,
    # mysql-data-dir/my.cnf to set server-specific options (in this
    # installation this directory is /var/lib/mysql) or
    # ~/.my.cnf to set user-specific options.
    # In this file, you can use all long options that a program supports.
    # If you want to know which options a program supports, run the program
    # with the “–help” option.

    # The following options will be passed to all MySQL clients
    #password = your_password
    port = 3306
    socket = /var/lib/mysql/mysql.sock

    # Here follows entries for some specific programs

    # The MySQL server
    port = 3306
    socket = /var/lib/mysql/mysql.sock
    key_buffer = 128M
    max_allowed_packet = 8M
    table_cache = 1024
    sort_buffer_size = 4M
    read_buffer_size = 4M
    read_rnd_buffer_size = 16M
    myisam_sort_buffer_size = 64M
    thread_cache_size = 16
    query_cache_size = 32M
    # Try number of CPU’s*2 for thread_concurrency
    thread_concurrency = 8

    # Don’t listen on a TCP/IP port at all. This can be a security enhancement,
    # if all processes that need to connect to mysqld run on the same host.
    # All interaction with mysqld must be made via Unix sockets or named pipes.
    # Note that using this option without enabling named pipes on Windows
    # (via the “enable-named-pipe” option) will render mysqld useless!

    # Replication Master Server (default)
    # binary logging is required for replication

    #required unique id between 1 and 2^32 – 1
    # defaults to 1 if master-host is not set
    # but will not function as a master if omitted
    server-id = 1

    # Replication Slave (comment out master section to use this)
    # To configure this host as a replication slave, you can choose between
    # two methods :
    # 1) Use the CHANGE MASTER TO command (fully described in our manual) –
    # the syntax is:
    # where you replace , , by quoted strings and
    # by the master’s port number (3306 by default).
    # Example:
    # CHANGE MASTER TO MASTER_HOST=’125.564.12.1′, MASTER_PORT=3306,
    # MASTER_USER=’joe’, MASTER_PASSWORD=’secret';
    # OR
    # 2) Set the variables below. However, in case you choose this method, then
    # start replication for the first time (even unsuccessfully, for example
    # if you mistyped the password in master-password and the slave fails to
    # connect), the slave will create a file, and any later
    # change in this file to the variables’ values below will be ignored and
    # overridden by the content of the file, unless you shutdown
    # the slave server, delete and restart the slaver server.
    # For that reason, you may want to leave the lines below untouched
    # (commented) and instead use CHANGE MASTER TO (see above)
    # required unique id between 2 and 2^32 – 1
    # (and different from the master)
    # defaults to 2 if master-host is set
    # but will not function as a slave if omitted
    #server-id = 2
    # The replication master for this slave – required
    #master-host =
    # The username the slave will use for authentication when connecting
    # to the master – required
    #master-user =
    # The password the slave will authenticate with when connecting to
    # the master – required
    #master-password =
    # The port the master is listening on.
    # optional – defaults to 3306
    #master-port =
    # binary logging – not required for slaves, but recommended

    # Point the following paths to different dedicated disks
    #tmpdir = /tmp/
    #log-update = /path-to-dedicated-directory/hostname

    # Uncomment the following if you are using BDB tables
    #bdb_cache_size = 384M
    #bdb_max_lock = 100000

    # Uncomment the following if you are using InnoDB tables
    #innodb_data_home_dir = /var/lib/mysql/
    #innodb_data_file_path = ibdata1:2000M;ibdata2:10M:autoextend
    #innodb_log_group_home_dir = /var/lib/mysql/
    #innodb_log_arch_dir = /var/lib/mysql/
    # You can set .._buffer_pool_size up to 50 – 80 %
    # of RAM but beware of setting memory usage too high
    #innodb_buffer_pool_size = 384M
    #innodb_additional_mem_pool_size = 20M
    # Set .._log_file_size to 25 % of buffer pool size
    #innodb_log_file_size = 100M
    #innodb_log_buffer_size = 8M
    #innodb_flush_log_at_trx_commit = 1
    #innodb_lock_wait_timeout = 50

    max_allowed_packet = 16M

    # Remove the next comment character if you are not familiar with SQL

    key_buffer = 256M
    sort_buffer_size = 256M
    read_buffer = 2M
    write_buffer = 2M

    key_buffer = 256M
    sort_buffer_size = 256M
    read_buffer = 2M
    write_buffer = 2M



    My server goes down when we add/update the content(means database operations).

    Thanks in Advance.