September 2012Sean Sullivan

@

• software engineer

• ~18 months at Gilt

• work in Gilt’s Portland office

• back office applications

About me

• Gilt Groupe

• Gilt’s technology stack

• MongoDB at Gilt

• Q&A

Agenda

Gilt Groupehttp://www.gilt.com

flash sales

Everyday at 12 noon

what does Gilt sell?

Apparel

Kids merchandise

Home furnishings

Food

Local deals

Travel

Gilt technology stack

Gilt architecture

monolithicapplication

service-oriented approach

2007 2012

2007

2012

service A

service B

service C

service D

service E

legacyweb app

gilt.com

Data storage @ Gilt

@

Why MongoDB?

• Ease of use

• Horizontal scaling

• High availability

• Automatic failover

Why MongoDB?

• Stability

• Support

• Drivers

• MongoDB 2.0

• sharded and non-sharded data

• Solid State Drives

• MMS for monitoring

Use case #1: user profiles

• user data in Postgres

• legacy Rails app expects to find user data in Postgres

• we want Gilt’s customer facing application code to retrieve user data from MongoDB

Challenges

• keep user data in both MongoDB and Postgres

• replicate table changes from Postgres to MongoDB

Solution

Replicating data

user service

legacyweb app

replication

Use case #2: feature configuration

Goal

manage the release of new features on gilt.com

How

feature configuration persisted in MongoDB

Rolling out a new feature

1. deploy new application code to production

2. enable feature for Gilt Tech employees

3. ... then enable for all Gilt employees

4. ... then enable for a subset of users

5. gradually ramp up to 100% of users

Feature configservice

Feature configuration

gilt.com

Use case #3: favorite brands

userpreference

service

AJAX

Favorite brands

Application development

mongo-java-driver

Morphia

Casbah

MongoDB Java driver

• main class: com.mongodb.Mongo

• Mongo object maintains a pool of connections

• Latest version: 2.9.1

MongoDB Java driver connection pool tuning

MongoOptions opts = new MongoOptions();

// example values

opts.connectionsPerHost = 50;

opts.threadsAllowedToBlockForConnectionMultiplier = 5;

com.mongodb.WriteConcern

• NORMAL

• SAFE

• REPLICAS_SAFE

• MAJORITY

• FSYNC_SAFE

• JOURNAL_SAFE

Morphia library

Morphia

• object-document mapper for Java

• built on top of mongo-java-driver

• map fields using Java annotations

// Morphia example

import com.google.code.morphia.annotations.*;

@Entity(value="features", noClassnameStored = true)

public class Feature {

@Id

ObjectId featureId;

@Property("feature_key") @Indexed(unique=true)

String featureKey;

@Property("release_to_percentage")

int releaseToPercentage;

}

http://code.google.com/p/morphia/

Casbah library

Casbah

• Scala toolkit for MongoDB

• built on top of the mongo-java-driver

Casbah

• Scala idioms

• Scala collections

• fluid query syntax

https://twitter.com/max4f/status/230503836958199808

Gilt Scala code

trait MongoWriteConcern {

def withSession[T](f: => T)(implicit mongoDb: MongoDB) {

mongoDb.requestStart()

mongoDb.requestEnsureConnection()

try {

f

} finally {

mongoDb.requestDone()

}

}

}

Best Practices

Best practices

Connection tuning

explicitly configure Mongo Java Driver connection pool size

Best practices

Use caution when creating new indexes

“creating a new index on a production mongo server can basically cause it to stop working while it builds the index”

(source: Gilt production incident report)

http://docs.mongodb.org/manual/administration/indexes/#index-building-replica-sets

Minimizing impact of building a new index

• remove one secondary from replica set

• create/rebuild index on this instance

• rejoin replica set

• repeat on all remaining secondaries

• run rs.stepDown() on primary member

Best practicesuse short names for fields to avoid wasted space

http://christophermaier.name/blog/2011/05/22/MongoDB-key-names

{

city: “Portland”,

state: “Oregon”,

country: “US”

}

{

ci: “Portland”,

st: “Oregon”,

co: “US”

}

vs

Best practices

use explain() during development

db.collection.find(query).explain()

Best practices

use caution when choosing a shard key

“It is generally not a good idea to use the default ObjectId as the shard key”

source: http://stackoverflow.com/questions/9164356/sharding-by-objectid-is-it-the-right-way

Future

• standardized read preferences

• tag aware sharding

MongoDB 2.2

Mongo Java driver 2.9.x

• enhanced read preference support

(see: com.mongodb.ReadPreference)

Gilt Groupe is hiring!http://techjobs.gilt.com

Questions?

ssullivan@gilt.com@tinyrobots

The end

Bonus slides

Gilt tech talks

• Apache Camel and MongoDB @ Gilt http://bit.ly/OYO37K

• Deploying new features @ Gilt http://slidesha.re/OoCYfd

• Voldemort @ Gilt

http://bit.ly/b9Qhib