I saw something interesting today when helping out someone on the #mysql IRC channel. It was a cnf file that was designed to destroy a server. Before I get into the why-not, here are the goods:

...snip...
read_buffer = 128M
join_buffer = 128M
key_buffer = 512M
max_allowed_packet = 200M
thread_stack = 192K
thread_concurrency = 8
thread_cache_size = 64
query_cache_limit = 256M
query_cache_size = 256M
table_cache = 8192
query_cache_type = 1
sort_buffer = 128M
record_buffer = 128M
myisam_sort_buffer_size = 128M
thread_cache = 64
max_user_connections = 500
wait_timeout = 200
max_connections = 4096
tmp_table_size = 1000M
max_heap_table_size = 1000M
...snip...


Now, you may ask why these settings are bad. I will tell you. First, an equation for calculating per-thread …

What would you like to see in a free enterprise-grade monitoring system for your daily MySQL needs?I’m rewriting Monolith - MySQL DBA Console from the ground up. This will be version 2 and I would like to get some input from the global MySQL community.So far I am going with the following; comment with any improvements/additions.

• Variable interval polling of server statistics
• Over 50 different alerts (see list below)
• Graphing of various server statistics (see list below)
• Tuning recommendations with cnf file changes to apply to server
• Change control documents for recommended performance/security tuning
• Threshold based alerting with multiple alert groups: info,warn,critical
• Sorting/ordering of servers via groups. ie: client -> dev,stage,prod
• RSS feeds for each alert group
• XML export with user defined fields for external applications …

A quick solution to a common problem: your MySQL server has thousands of connections, some or most are not persistent. Unless you say otherwise, MySQL will check connections hostnames against the system DNS server. While this is generally not a problem with low traffic, when you are dealing with many concurrent connections you are not only wasting cycles with DNS name resolve, you may also overwhelm or alert your DNS server/provider. The solution? Set skip-name-resolve in the my.cnf file and MySQL will run the connections off of their IP address instead of the DNS name that it resolves to.