LAZY
INDEXING
matt aimonetti
sdruby

before we start
I’m not a Database Administrator
This talk only covers MySQL
You will still need to understand indexing
Dubbed version of this presentation will be available
from Patrick ;)

indexing
SELECT * FROM users
WHERE last_name = 'Aimonetti';
NO INDEX
look at each row in the table, one at a time, to find all
matching records
(full table scan = SLOW)

indexing
SELECT * FROM users
WHERE last_name = 'Aimonetti';
INDEX
simply follows the b-tree data structure until the
Aimonetti entries have been found = WAY FASTER

indexing
class User < ActiveRecord::Base
has_many :team_members, :dependent => :destroy
has_many :projects, :through => :team_members
end
current_user.projects
SELECT `projects`.* FROM `projects` INNER JOIN team_members
ON projects.id = team_members.project_id
WHERE ((`team_members`.user_id = 1))

indexing
how to know
what indexes to create?

indexing N?
HE
W
Every time you are using one of these
associations in a model:
belongs_to,
has_many,
has_one,
or has_and_belongs_to_many association

indexing N?
HE
W
✓ use a join in your query
✓query non-foreign-key column
✓ sort on a column or combination of columns

T?
indexing HA
W
EXPLAIN
obtain information about how MySQL
executes a SELECT statement

indexing
query-reviewer plugin
http://code.google.com/p/query-reviewer/
by Kongregate and David Stevenson

indexing
add an index from your migrations:
add_index :invoices, [:client_id, :invoiced_on]
remove an index from your migrations:
remove_index :invoices, [:client_id, :invoiced_on]

indexing
resources:
http://code.google.com/p/query-reviewer/
http://weblog.jamisbuck.org/2006/10/23/indexing-for-db-performance
http://www.mysqlperformanceblog.com/