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Install
sudo apt-get install mysql-server -y; sudo apt-get install handlersocket-doc -y; sudo apt-get install handlersocket-mysql-5.1 -y; sudo apt-get install libhsclient-dev -y;
Configure
#/etc/mysql/my.cnf -- under mysqld section loose_handlersocket_port = 9998 loose_handlersocket_port_wr = 9999 loose_handlersocket_threads = 16 loose_handlersocket_threads_wr = 1 open_files_limit = 65535
Start
mysql -e "install plugin handlersocket soname 'handlersocket.so';" sudo /etc/init.d/mysql restart # should show lots of handlersocket processes mysql -e "show processlist;"
Use
gem install handlersocket require 'handlersocket' h = HandlerSocket.new(:host => '127.0.0.1', :port => '9998') # open PRIMARY index on widgets.user table, assign it ID #1 h.open_index(1, 'widgets', 'user', 'PRIMARY', 'user_name,user_email,created') ...
more of this can be found at ruby handlersocket introduction and ActiveRecord Handlersocket gem
Starting point
Normally there is a table with some small stuff like id/type/xxx_id(~50B) and a text column(default 768B + x) that is not needed all the time, because most users enter less than 255 chars or most queries only need the smaller columns.
- text bloats table size
- text makes queries slow
- text bloats mysql query cache
- text is always loaded into buffer pool (consumes ram)
Alternative Row format
With row ROW_FORMAT=DYNAMIC those default 768B+x can be reduced to a mere default 20B+x, but requires innodb_file_format=Barracuda.
1 to 1 Relationship
Keep all small columns on the first model and pull in the text from another model e.g. using translated_attributes.
Generates some overhead in the model but is reasonably fast.
Varchar column as cache + 1 to 1 Relationship
Only fetches the text/adds the relationship when needed. Useful when only a few texts are larger then 255 chars and the content is often needed. e.g. on original model:
def text_truncated(to=255)
text = if to > 255 and text_cache.size == 255
1_to_1_relationship.text
else
text_cache
end
text.truncate(to)
end
(this needs truncate on string)
And e.g. in the UI the text could always show truncated to 255 chars and only on click it is really loaded from the db.
Using covering index
Make an index that covers all the normal columns except the text, and FORCE INDEX on the queries.
Performance
Source:
A lot more details on the 1-to-1-relation ship / covering index can be found here
Changing many columns is not so easy, because change_column forces you to enter all attributes you want (default,limit,null…) again.
So to make less errors we just alter the attributes we want to change and leave the rest alone.
Install
#Inside your migration
def self.alter_column(table,column,text)
execute("ALTER TABLE #{quote_table_name(table)} ALTER #{quote_column_name(column)} #{text}")
end
Usage
# to set the default to nil, without remembering all the other # stuff change_column needs alter_column(:users,:name,"DROP DEFAULT")
So thats very basic, but i hope it helps anyway 
I just came across a serious bug/gotcha when using mysql.
Integer, default 0 -> set to NULL –> NULL and not 0
Remember
always set NOT_NULL and DEFAULT!
Example
change_columnrder_items, :shipping, :boolean, :default=>false #shipping is nil or false or true OrderItem.find(:all,:conditions=>{:shipping=>false}) => [] change_column
