Sep 27, 2010

MySQL optimization (I)

When MySQL is installed by a software packages manager such as yum or aptitude, we get instantly a valid database server ready to work.

It turns out that installation is performed with a series of settings applied by default, which are not the most optimal for our system in most cases, since there are many more variables (memory, CPU, other services configured, etc.) that we have to consider.

Therefore, it is the best that once the databases have been created, to leave a margin large enough time (for example a couple of days) to make the system stable and to be able to acquire its real work load.

In that moment , we can apply any sort of MySQL optimization or tunning tool, such as MySQL Performance Tuning Primer Script or MySQLTuner.

Then we are going to use the first tool on a Zabbix 1.8.1 installation, utilizing CentOS 5.4 64 bits with a MySQL 5.0.77 database.

[root@centos ~]# ./

Using login values from ~/.my.cnf
Testing for stored webmin passwords:
None Found
Could not auto detect login info!
Found Sockets: /var/lib/mysql/mysql.sock
Using: /var/lib/mysql/mysql.sock
Would you like to provide a different socket?: [y/N]
Do you have your login handy ? [y/N] : y
User: root

Would you like me to create a ~/.my.cnf file for you? [y/N] :

     - By: Matthew Montgomery -

MySQL Version 5.0.77 x86_64

Uptime = 2 days 0 hrs 53 min 41 sec
Avg. qps = 19
Total Questions = 3375129
Threads Connected = 15

Server has been running for over 48hrs.
It should be safe to follow these recommendations

To find out more information on how each of these
runtime variables effects performance visit:
for info about MySQL's Enterprise Monitoring and Advisory Service

The slow query log is NOT enabled.
Current long_query_time = 10 sec.
You have 0 out of 3375150 that take longer than 10 sec. to complete
Your long_query_time seems to be fine

The binary update log is NOT enabled.
You will not be able to do point in time recovery

Current thread_cache_size = 0
Current threads_cached = 0
Current threads_per_sec = 1
Historic threads_per_sec = 0
Your thread_cache_size is fine

Current max_connections = 100
Current threads_connected = 15
Historic max_used_connections = 21
The number of used connections is 21% of the configured maximum.
Your max_connections variable seems to be fine.

Current InnoDB index space = 112 M
Current InnoDB data space = 240 M
Current InnoDB buffer pool free = 0 %
Current innodb_buffer_pool_size = 8 M
Depending on how much space your innodb indexes take up it may be safe
to increase this value to up to 2 / 3 of total system memory

Max Memory Ever Allocated : 75 M
Configured Max Per-thread Buffers : 274 M
Configured Max Global Buffers : 17 M
Configured Max Memory Limit : 292 M
Physical Memory : 1.96 G
Max memory limit seem to be within acceptable norms

Current MyISAM index space = 71 K
Current key_buffer_size = 7 M
Key cache miss rate is 1 : 6
Key buffer free ratio = 81 %
Your key_buffer_size seems to be fine

Query cache is supported but not enabled
Perhaps you should set the query_cache_size

Current sort_buffer_size = 2 M
Current read_rnd_buffer_size = 256 K
Sort buffer seems to be fine

Current join_buffer_size = 132.00 K
You have had 4 queries where a join could not use an index properly
You should enable "log-queries-not-using-indexes"
Then look for non indexed joins in the slow query log.
If you are unable to optimize your queries you may want to increase your
join_buffer_size to accommodate larger joins in one pass.

Note! This script will still suggest raising the join_buffer_size when
ANY joins not using indexes are found.

Current open_files_limit = 1024 files
The open_files_limit should typically be set to at least 2x-3x
that of table_cache if you have heavy MyISAM usage.
Your open_files_limit value seems to be fine

Current table_cache value = 64 tables
You have a total of 105 tables
You have 64 open tables.
Current table_cache hit rate is 0%
, while 100% of your table cache is in use
You should probably increase your table_cache

Current max_heap_table_size = 16 M
Current tmp_table_size = 32 M
Of 85195 temp tables, 31% were created on disk
Effective in-memory tmp_table_size is limited to max_heap_table_size.
Perhaps you should increase your tmp_table_size and/or max_heap_table_size
to reduce the number of disk-based temporary tables
Note! BLOB and TEXT columns are not allow in memory tables.
If you are using these columns raising these values might not impact your
ratio of on disk temp tables.

Current read_buffer_size = 128 K
Current table scan ratio = 0 : 1
read_buffer_size seems to be fine

Current Lock Wait ratio = 0 : 3375450
Your table locking seems to be fine

When we run the second tool, we pick up the following information:

[root@centos ~]# ./

>>  MySQLTuner 1.0.1 - 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 5.0.77
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -------------------------------------------
[--] Status: -Archive +BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in InnoDB tables: 240M (Tables: 88)
[!!] BDB is enabled but isn't being used
[OK] Total fragmented tables: 0

-------- Performance Metrics -------------------------------------------------
[--] Up for: 2d 0h 56m 0s (3M q [19.168 qps], 23K conn, TX: 530M, RX: 331M)
[--] Reads / Writes: 69% / 31%
[--] Total buffers: 34.0M global + 2.7M per thread (100 max threads)
[OK] Maximum possible memory usage: 309.0M (15% of installed RAM)
[OK] Slow queries: 0% (0/3M)
[OK] Highest usage of available connections: 21% (21/100)
[OK] Key buffer size / total MyISAM indexes: 8.0M/67.0K
[!!] Key buffer hit rate: 85.3% (239K cached / 35K reads)
[!!] Query cache is disabled
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 14K sorts)
[!!] Temporary tables created on disk: 31% (38K on disk / 123K total)
[!!] Thread cache is disabled
[!!] Table cache hit rate: 0% (64 open / 9K opened)
[OK] Open file limit used: 0% (0/1K)
[OK] Table locks acquired immediately: 100% (3M immediate / 3M locks)
[!!] InnoDB data size / buffer pool: 240.7M/8.0M

-------- Recommendations -----------------------------------------------------
General recommendations:
Add skip-bdb to MySQL configuration to disable BDB
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:
query_cache_size (>= 8M)
tmp_table_size (> 32M)
max_heap_table_size (> 16M)
thread_cache_size (start at 4)
table_cache (> 64)
innodb_buffer_pool_size (>= 240M)

In the next two article, we will see how to fit these values.