Using Amazon Simple Db With Rails

Using Amazon SimpleDB
with Rails

http://webonrails.com

Amazon SimpleDB
● Database web service advertised as:
● Simple, Flexible, Scalable, Fast, Reliable, Inexpensive

● No RDBMS: no SQL, no joins, no schema,
no referential integrity, no transactions

● Ability to store, process and query data
sets


Amazon SimpleDB
● HTTP-Interface

● Pricing: Similar to other AWS


Before we move
Further


Let, have a look

at

Amazon SimpleDB
Common Terms


Amazon SimpleDB Common
Terms
● Domain:
storage container ~ table

● Item:
~ table rows accessed by ID ~ primary key

● Attribute:
~ table columns; every item may have a different
set of upto 256 attributes

Amazon SimpleDB Common
Terms
● Value:
each Attribute may havemultiple Values, always
varchar(1024)[]


SimpleDB

Domain A
Attributes
Items

Values (multiple)


PUT (item, 123),
(description, sweater),
(color, blue),
(color, red)

PUT (item, 456),
(description, dress shirt),
(color, white),
(color, blue)


Amazon SimpleDB API

● Domain level:
● CREATE, LIST, DELETE

● Item level:
● GET, PUT, DELETE attributes with values
● QUERY for unordered item IDs by
attribute values within one domain

● Beware: Eventual Consistency Approach!

Benefits over traditional databases

● No need to pre-define data types
● 'Size' can be 9 or XL or 1.5
● Add attributes anytime
● Attributes specifically for some items
● Index all data


API Summary

● CreateDomain — Create a domain(100).
● DeleteDomain — Delete a domain.
● ListDomains — List all domains.
● DomainMetadata — Retrieve information
about the domain.


API Summary

● PutAttributes — Add or update an item and
its attributes, or add attribute-value pairs to
items that exist already.
● GetAttributes — Retrieve an item and all or
a subset of its attributes and values.
● DeleteAttributes — Delete an item, an
attribute, or an attribute value.


API Summary

● Query — Query the dataset using a query
expression which specifies value tests on
one or more attributes.

● Supported value tests are:
=, !=, <, > <=, >=, starts-with.
[“price” < “12.00”] INTERSECTION [“color” = “green”].

● Order results using the SORT operator

API Summary

● QueryWithAttributes — Enables developers
to retrieve all or a subset of the information
associated with items returned as a
response to a particular query.


SimpleDB vs S3
S3 SimpleDB
● Stores raw data ● Stores indexed data

● Uses higher dense ● Uses less dense
storage drives storage drives


SimpleDB Limits (Cont...)
● Domain size 10 GB per domain
● Domain size 250,000,000 attribute name-
value pairs
● Domain name 3-255 characters
● Domains per account 100
● Attribute name-value pairs/item 256
● Attribute name length 1024 bytes
● Attribute value length 1024 bytes
● Item name length 1024 bytes
● All UTF-8 characters that are valid in XML documents are
allowed in name/value.


SimpleDB Limits

● Attributes per PutAttributes operation 100
● Maximum items in query response 250
● Maximum query execution time 5 seconds
● Maximum comparisons per predicate 10
● Maximum predicates per query 10
expression
● Maximum response size for 1MB
QueryWithAttributes


Working with Numerical Data

● SimpleDB is a schema-less data store
● Everything is stored as a UTF-8 string value



● Ensure that every number is positive



● Ensure that every number is positive

What about Negative
Numbers?


Negative Numbers Offsets

● Choose an offset
● That should be arger than the smallest
expected negative number in your data set
● Ex:
● if the smallest expected number in your data set is -12,
choosing offset = 100 might be safe


Negative Numbers Offsets

The following is a sample original data set.
14.58, -12.7, 20, 65, -23

If you apply an offset of 100 the following is the resulting
data set:

114.58, 87.3, 120, 165, 77


Zero Padding

● Since simpleDB uses lexicographical
comparisons “10” comes before “2”
● If we zero pad the numbers to five digits,
quot;00002quot; comes before quot;00010quot;


Dates
● ISO 8601 format


Query dataset

['attribute1' = 'value1']
intersection
not ['attribute2' = 'value2']
union
['attribute3' = 'value3']


SimpleDB with Rails

AWS SDB
Proxy Plugin


SimpleDB with Rails

● Install aws-sdb gem
● gem install aws-sdb

● Install aws_sdb_proxy plugin:
● script/plugin install
git://github.com/bansalakhil/aws_sdb_proxy.git

*Plugin originaly written by martin.rehfeld@glnetworks.de


AWS SDB Proxy Plugin

● Configure config/aws_sdb_proxy.yml
● development:
aws_access_key_id: <aws key>
aws_secret_access_key: <aws secret key>
port: 8888

● Create new domain on Amazon SimpleDB
● rake aws_sdb:create_domain DOMAIN=MyDataStore


AWS SDB Proxy Plugin

● Start AWS SDB proxy
● rake aws_sdb:start_proxy_in_foreground


Mapping RESTful URLs


Using AWS SDB Proxy Plugin

● Create demo ActiveResource model

class Post < ActiveResource::Base
self.site = quot;http://localhost:8888quot;
self.prefix = quot;/MyDataStore/quot;
end


Lets try at script/console
>> Article.create(:title => quot;This is my First articlequot;)
=> #<Article:0xb7005d04 @attributes={quot;updated_atquot;=>Sat Dec 13
15:53:30 UTC 2008, quot;titlequot;=>quot;This is my First articlequot;,
quot;idquot;=>601834...98, quot;created_atquot;=>Sat Dec 13 15:53:30 UTC 2008},
@prefix_options={}>
>> a = Article.create(:title => quot;This is my Second articlequot;)
=> #<Article:0xb6fe1f08 @attributes={quot;updated_atquot;=>Sat Dec 13
15:53:52 UTC 2008, quot;titlequot;=>quot;This is my Second articlequot;,
@prefix_options={}>
>> a.body = quot;Nothingquot;
>> a.save
=> true


Lets try at script/console
>> Article.find(:all).size
=> 2
>> Article.find(:all, :from => :query, :params => quot;['title' starts-with 'This
is' ]quot;)
=> [#<Article:0xb6f73080 @attributes={quot;updated_atquot;=>Sat Dec 13
15:53:30 UTC 2008, quot;titlequot;=>quot;This is my First articlequot;, quot;idquot;=>60...98,
quot;created_atquot;=>Sat Dec 13 15:53:30 UTC 2008},
@prefix_options={}>, #<Article:0xb6f7306c
@attributes={quot;updated_atquot;=>Sat Dec 13 15:54:14 UTC 2008,
quot;bodyquot;=>quot;Nothingquot;, quot;titlequot;=>quot;This is my Second articlequot;,
@prefix_options={}>]


References

● http://aws.amazon.com/simpledb/
● http://inside.glnetworks.de


Thanks
Akhil Bansal


Using Amazon Simple Db With Rails

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