Rails database optimization

Database Optimization

Scaling
Ruby-on-Rails
By Example
Karsten Meier
meier-online.com

My Technical Background
●

1986: SQL at university

●

1996: QuarkXpress -> HTML Converter

●

1998-2001: WebObjects, MVC, ORM

●

2004: First contact with Ruby (Pleac)

●

Since 2005: Handylearn Projects

●

Since 2009: Use of Rails in projects

2

Use Case: Cycosmos
●

Community

●

Webobjects

●

●

ORM
Enterprise Objects
3 Appserver,
1 DB Server

3

Effects Of Less Database Queries
●

●
●

●

Better response
times
Less database load
300% higher
throughput
Higher stability

Fat Objects
imo

id
teu

grt

call_sign

build_year

name
speech_of_sponsor

draft
machine

imo_certificate
company

legal_country

Schadow Objects
ContainerVessel.
select('id, name')
order('name')
●

Read-Only

●

Only given attributes

●

●

Exception
if unknown

ActiveRecord::ReadOnlyRecord

ActiveRecord::MissingAttributeError

ID does not throw
exception

Cherrypicking
●

Only one column

●

Object not needed

●

pluck(column)

●

since Rails 3.2

ContainerVessel.pluck(:name)
['Australia', 'Brisbane', 'Busan',...]

Outsourcing
●

Weight of all container on the vessel?

●

DB can do the calculation

●

Rails does not see the individual containers
@vessel.containers.inject{...}
@vessel.containers.sum('weight')

Linked Objekts
●

A company with a list of vessels, each with a
flag country

includes()
@container_vessels =
@company.container_vessels.
order(:name).
includes(:legal_country)
SELECT "container_vessels".*
FROM "container_vessels"
WHERE "container_vessels"."company_id" = 2
ORDER BY name
SELECT "countries".*
FROM "countries"
WHERE "countries"."id" IN (8, 7, 4)

includes()
●

Each query returns objects of one type

●

Rails always in control

●

Nesting possible

●

Fine tuning difficult
.includes(:legal_country => :tax_rates)
.select('country.image????')

Rails joins
@container_vessels =
@company.container_vessels.
order(:name).
joins(:legal_country)
●

●

No vessels without a
flag state
No country data

Filter with joins()
●

Filter with conditions in linked data

●

Only target objects are returned

●

Beware possible duplications!

@companies = Company.order(:name).
joins(:container_vessels).
where(["container_vessels.build_year > ?", 2009])
SELECT "companies".*
FROM "companies"
INNER JOIN "container_vessels"
ON "container_vessels"."company_id" = "companies"."id"
WHERE (container_vessels.build_year > 2009)
ORDER BY name

Automatic Join
in Associations
class Country < ActiveRecord::Base
has_many :registering_companies,
:through => :registered_vessels,
:source => 'company',
:class_name => 'Company',
:uniq => true
...
@companies = @country.registering_companies
SELECT DISTINCT "companies".*
FROM "companies"
INNER JOIN "container_vessels"
ON "companies"."id" = "container_vessels"."company_id"
WHERE "container_vessels"."legal_country_id" = 10

Real Database Joins In Rails
connection = Company.connection
columns = "container_vessels.id, container_vessels.name,
container_vessels.imo, container_vessels.teu,
countries.name as legal_country_name"

sql = 'SELECT ' + columns + ' FROM "container_vessels"
JOIN "countries"
ON "countries"."id" = "container_vessels"."legal_country_i
WHERE "container_vessels"."company_id" = ' + @company.id.t
' ORDER BY "container_vessels".name'
@vessel_data = connection.select_all(
sql, 'ContainerVessel Overview Load')

Returned Values
●

select_all: array of hashes

●

select_rows: array of arrays

<% @vessel_data.each do |data| %>
<tr>
<td><%= data['name'] %></td>
<td><%= data['imo'] %></td>
<td><%= data['teu'] %></td>
<td><%= data['legal_country_name'] %></td>
...
<% end %>

Checking Parameters
●
●

●

●

SQL-Injection
Methods difficult to
find
Since Rails 3.2:
ActiveRecord::
Sanitization
For IDs: to_i.to_str

Company.where(
'name like '%?', input)
record.sanitize_sql_array(..)
replace_bind_variables()
quote_bound_value()
connection.quote_string()

Writing
If you have performance problems during
writing, the implications are often bad.

IDs
●

●

ID-delivery can be a
central bottle neck
Sometimes already
existing IDs can be
used

Transactions
●

Ensure consistency (ACID)

●

Less locking, faster writes

●

Use them if you have more than one write
operation in an action

Mass Updates
●

Company is sold

●

All vessels get a new owner

UPDATE container_vessels
SET company_id = 7
WHERE company_id = 5

connection.update_sql(sql, "Updating vessel...")

Linked Updates
●
●

Example usage: denormalisation
Name of country should also be stored in
vessel table

UPDATE container_vessels, country
SET container_vessels.country_name = country.name
WHERE container_vessels.legal_country_id = country.id

Don't be afraid of SQL

"Many people treat the relational database
like a crazy aunt who's shut up in an attic
and whom nobody wants to talk about"
Martin Fowler: OrmHate

... end
Website of Karsten Meier:

meier-online.com
Pictures:
Container ship by jogdragoon, openclipart.org
Hammer5 by Krystof Jetmar, openclipart.org
OOCL Montreal & Cosco Hope photos by Karsten Meier in port of Hamburg 2012

Rails database optimization

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