Reducing memory consumption of mysql on ubuntu@aws micro instance

In your /etc/my.cnf file:

performance_schema = 0

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

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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

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

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