Reducing memory consumption of mysql on ubuntu@aws micro instance

Question

I have recently started on a PoC project wherein we are developing a small web app. The initial setup is done on a micro instance from AWS. We are on rails+mysql stack.

Answer 1

I have a server with only 500mb ram and found that mysql started using a lot of ram as my tables got larger. After playing with a bunch of the settings, what reduced memory usage for me was to convert all my tables to MyISAM. If you dont need the features of innodb converting tables to MyISAM helps quite a bit. You can convert tables like this :

ALTER TABLE test.mytable ENGINE=MyISAM;

After this change I found that memory usage decreased by 20%. To get a further reduction in memory usage you can convert ALL of your tables to MyISAM and then turn off innodb support in mysql altogether. This reduced my memory usage by 50%.

You can do this by adding :

[mysqld]
default_storage_engine=myisam
innodb=OFF

and then restarting mysql.

Answer 2

In your /etc/my.cnf file:

performance_schema = 0

And restart MySQL. This should chop memory usage dramatically if you previously had it on.

---

Edit: For MySQL versions between 5.7.8 and 8.0.1 (not required from 8.0.1 onwards), the above is not enough to free your memory of performance schema data:

As of MySQL 5.7.8, even when the Performance Schema is disabled, it continues to populate the global_variables, session_variables, global_status, and session_status tables.

(source)

To prevent this behaviour, set show_compatibility_56 to 1 in addition to performance_schema. That is to say, your my.cnf changes should look like:

performance_schema = 0
show_compatibility_56 = 1

Answer 3

Just to add to the other answer. I recently had this problem myself with the Amazon micro instance (not Ubuntu). The my.cnf file is almost empty so what I did was this:

cp /etc/my.cnf /etc/my.cnf.orig
cp /usr/share/mysql/my-medium.cnf /etc/my.cnf

Edit my.cnf and enable the innodb lines if applicable. Restart mysqld.

Also the micro instance has no swap, that might be a problem..

SWAPFILE=/mnt/swapfile.swap
dd if=/dev/zero of=$SWAPFILE bs=1M count=512
mkswap $SWAPFILE
swapon $SWAPFILE

Then in /etc/rc.local add:

swapon /mnt/swapfile.swap

To save memory in ruby you might want to use ruby enterprise:

bash < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)
gpasswd -a root rvm
source /etc/profile.d/rvm.sh
rvm get head
rvm reload
rvm install ree
rvm --default use ree

Answer 4

Change this setting in the MySQL configuration file (my.cnf)

key_buffer              = 8M 
max_connections         = 30 # Limit connections
query_cache_size        = 8M # try 4m if not enough 
query_cache_limit       = 512K
thread_stack            = 128K