Reduce MySQL memory usage

As I am running more and more on my 256mb slice, I’m trying to squeeze more performance out of the system. After a bit of digging, I’ve made a few changes.

First thing I did was switch out the default mysql config with one tweaked for smaller boxes. This configuration actually came with the mysql installation under /usr/share/doc/mysql-server-5.0/examples/. Just backup your existing my.cnf (mine is located under /etc/mysql) and use the following:

# The following options will be passed to all MySQL clients
port		= 3306
socket		= /var/run/mysqld/mysqld.sock

# Here follows entries for some specific programs

# The MySQL server
port		= 3306
socket		= /var/run/mysqld/mysqld.sock
key_buffer = 16K
max_allowed_packet = 1M
table_cache = 4
sort_buffer_size = 64K
read_buffer_size = 256K
read_rnd_buffer_size = 256K
net_buffer_length = 2K
thread_stack = 64K

# 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
# (using the "enable-named-pipe" option) will render mysqld useless!
server-id	= 1

# Uncomment the following if you want to log updates

# Uncomment the following if you are NOT using BDB tables

# Uncomment the following if you are using InnoDB tables
#innodb_data_home_dir = /var/lib/mysql/
#innodb_data_file_path = ibdata1:10M: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 = 16M
#innodb_additional_mem_pool_size = 2M
# Set .._log_file_size to 25 % of buffer pool size
#innodb_log_file_size = 5M
#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 = 8M
sort_buffer_size = 8M

key_buffer = 8M
sort_buffer_size = 8M


You can see estimated memory usage with a config if you just copy paste the configuration file here.

Restart MySQL (/etc/init.d/mysql restart).

The second thing I did was check out MySQLTuner. Just download the perl script and run it. It will run some analysis on your mysql setup and provide some performance and configuration tweak recommendations.

Sample output looks like this:

 >>  MySQLTuner 1.0.0 - Major Hayden 
 >>  Bug reports, feature requests, and downloads at
 >>  Run with '--help' for additional options and output filtering
Please enter your MySQL administrative login: root
Please enter your MySQL administrative password: 

-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.0.51a-3ubuntu5.4
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -------------------------------------------
[--] Status: +Archive -BDB -Federated +InnoDB -ISAM -NDBCluster 
[--] Data in MyISAM tables: 867K (Tables: 18)
[--] Data in InnoDB tables: 704K (Tables: 40)
[!!] Total fragmented tables: 2

-------- Performance Metrics -------------------------------------------------
[--] Up for: 14h 57m 0s (17K q [0.316 qps], 699 conn, TX: 55M, RX: 3M)
[--] Reads / Writes: 96% / 4%
[--] Total buffers: 26.0M global + 824.0K per thread (100 max threads)
[OK] Maximum possible memory usage: 106.5M (41% of installed RAM)
[OK] Slow queries: 0% (0/17K)
[OK] Highest usage of available connections: 6% (6/100)
[!!] Key buffer size / total MyISAM indexes: 16.0K/381.0K
[!!] Key buffer hit rate: 88.5% (154K cached / 17K reads)
[!!] Query cache is disabled
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 4K sorts)
[!!] Temporary tables created on disk: 30% (1K on disk / 4K total)
[!!] Thread cache is disabled
[!!] Table cache hit rate: 0% (4 open / 7K opened)
[OK] Open file limit used: 0% (8/1K)
[OK] Table locks acquired immediately: 99% (17K immediate / 17K locks)
[OK] InnoDB data size / buffer pool: 704.0K/8.0M

-------- Recommendations -----------------------------------------------------
General recommendations:
    Run OPTIMIZE TABLE to defragment tables for better performance
    MySQL started within last 24 hours - recommendations may be inaccurate
    Enable the slow query log to troubleshoot bad queries
    When making adjustments, make tmp_table_size/max_heap_table_size equal
    Reduce your SELECT DISTINCT queries without LIMIT clauses
    Set thread_cache_size to 4 as a starting value
    Increase table_cache gradually to avoid file descriptor limits
Variables to adjust:
    key_buffer_size (> 381.0K)
    query_cache_size (>= 8M)
    tmp_table_size (> 32M)
    max_heap_table_size (> 16M)
    thread_cache_size (start at 4)
    table_cache (> 4)

I haven’t made any of the recommended changes yet though. I am going to try to see how this default small config performs.

I’ll try to follow up with any of my findings.

Reduce MySQL memory usage