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Push databases, RethinkDB, and building realtime apps Move Fast and Break Things San Francisco, CA August 5, 2015

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Jorge Silva Developer Evangelist @ RethinkDB @thejsj

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Preface The realtime web

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Realtime apps

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Realtime apps

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Realtime apps • More and more apps are built to be realtime • Users have come to want and expect this behavior in their apps • Building realtime apps is hard

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Building realtime apps is hard • You can keep everything in a single server • You can poll the database to keep track of updates • You can publish updates through 
 a message broker

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Building realtime apps is hard • All solutions present a tradeoff between scalability and complexity • It’s hard to keep track of state in 
 realtime architectures

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Introduction What is RethinkDB?

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What is RethinkDB? • Open source database for building realtime web applications • NoSQL database that stores schemaless JSON documents • Distributed database that is easy to scale

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Push Database • Subscribe to change notifications from database queries (changefeeds) • No more polling — the database pushes changes to your app • Reduce the amount of plumbing needed to stream live updates

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Push Database • Having your database push changes keeps your database as the central source of truth • Having a central source of truth simplifies your architecture

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Push Database RethinkDB is an excellent database for: • Collaborative web and mobile apps • Multiplayer games • Streaming analytics apps • Connected devices

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Introduction to ReQL RethinkDB Query Language

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Introduction to ReQL • ReQL embeds natively into your programming language • Compose ReQL queries by chaining commands

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Anatomy of a ReQL Query r.table("users") .pluck("last_name") .distinct().count() Number of unique last names

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Anatomy of a ReQL Query r.table("users") .pluck("last_name") .distinct().count() Access a database table

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Anatomy of a ReQL Query r.table("users") .pluck("last_name") .distinct().count() Isolate a document property

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Anatomy of a ReQL Query r.table("users") .pluck("last_name") .distinct().count() Consolidate duplicate values

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Anatomy of a ReQL Query r.table("users") .pluck("last_name") .distinct().count() Display the number of items

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Sample ReQL Queries r.table("users") .filter(r.row("age").gt(30)) r.table(“post") .eqJoin(“uId”, r.table(“users”)) .zip() r.table("fellowship") .filter({species: "hobbit"}) .update({species: "halfling"})

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Additional ReQL Features • Geospatial indexing for location- based queries • Date and time functions • Support for storing binary objects • Execute http requests using r.http

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Realtime Updates Working with Changefeeds

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Subscribe to change notifications on database queries Changefeeds

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r.table("users").changes() Track changes on the users table Changefeeds

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Changefeeds • The changes command returns a cursor that receives updates • Each update includes the new and old value of the modified record

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Changefeeds r.table("users").changes() r.table("users") .insert({name: "Bob"}) Changefeed output: { new_val: { id: '362ae837-2e29-4695-adef-4fa415138f90', name: 'Bob', ... }, old_val: null }

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Changefeeds r.table("users").changes() r.table("users") .filter({name: "Bob"}).delete() Changefeed output: { new_val: null, old_val: { id: '362ae837-2e29-4695-adef-4fa415138f90', name: 'Bob', ... } }

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Changefeeds r.table("users").changes() r.table("users") .get("362ae837-2e29-4695-adef-4fa415138f90") .update({name: "Bobby"}) Changefeed output: { new_val: { id: '362ae837-2e29-4695-adef-4fa415138f90', name: 'Bobby' }, old_val: { id: '362ae837-2e29-4695-adef-4fa415138f90', name: 'Bob' } }

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Changefeeds r.table("players") .orderBy({index: r.desc("score")}) .limit(3).changes() Track top three players by score Chain the changes command to an actual ReQL query:

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Questions http://questions.rethinkdb.com

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Summary • Keeping track of state in realtime apps is hard • RethinkDB solves this problem by pushing changes to your app • In the future, we'll see more database that use the push model

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Questions • RethinkDB website:
 http://rethinkdb.com • Install RethinkDB:
 http://rethinkdb.com/install/ • Email me: jorge@rethinkdb.com • Tweet: @thejsj, @rethinkdb