Stateful Applications in a Stateless World
How to write stateful web
applications that scale like
stateless ones
Copyright Terracotta 2007

Open Source Clustering for Java
The Innocent Web Application
 Within every innocent web application lies a sleeping monster
 There comes a time when every successful web application
outgrows its single machine architecture
 Whether for high-availability or scalability or both, the adult web
application must live on more than one application server
 That's when the latent beast strikes...
Copyright Terracotta 2007

Open Source Clustering for Java
The State Monster
Copyright Terracotta 2007

Open Source Clustering for Java
The State Monster
 Conversational state across requests
 Application state: caches, indexes,
etc.
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention
 Push state out of your application server to achieve
\"statelessness\"
 Application server is for computation only
 Any application server can handle any request
 \"...with a little ingenuity, [we have created a] very fast
application that is much more resilient to application restarts\"
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Push State to the Database
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Push State to the Database
 DB becomes a bottleneck
 Not optimized for object data
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Push State to Peers
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Push State to Peers
 Push state everywhere gives HA, but doesn't scale
 Push conversational state to buddy can't survive buddy pair death or
full cluster restart. Doesn't help for application state.
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Push State to Client
 Highly scalable for conversation state UNLESS state is large
 Doesn't help with application state
Copyright Terracotta 2007

Open Source Clustering for Java
Stateless Convention: The Real Problem
\"With a little ingenuity,\" many of these problems can be solved on
a per-application basis.
The real problem with the \"stateless\" convention is...
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Eats Developer Brains
Copyright Terracotta 2007

Open Source Clustering for Java
The Stateless Convention: Eats Developer Brains
 Pushing state out of app server
doesn't get rid of state. There
is no such thing as \"stateless\"
 Serialization/externalization:
 Full-object graph serialization
 breaks object identity
 corrupts data and programming
model
 \"with a little ingenuity...\"--
seems fun/easy to try, but ends
up taking over the development
effort
Copyright Terracotta 2007

Open Source Clustering for Java
Changing the Assumptions: JVM-level Clustering
Copyright Terracotta 2007

Open Source Clustering for Java
Performance + Reliability + Simplicity
 10X throughput over conventional APIs
 All Reads from Cache (implicit locality)
 All Writes are Deltas-only
 Statistics and Heuristics (greedy locks)
 Scale out the Terracotta Server
 Simple form of Active / active available today
 V1.0 GA this year
 Looks like Java to me (code like your mom used to make)
Normal access patterns: no check-out before view and check-in on commit

Code and test at a unit level without infrastructure intruding on app logic

Threads on multiple JVMs look like threads on the same JVM

PUFIELD, GETFIELD, synchronized(), wait(), notify() work as expected

Copyright Terracotta 2007

Open Source Clustering for Java
Demo: Session Clustering
Copyright Terracotta 2007

Open Source Clustering for Java
Demo: CoordinationWithQueues (from our Apress book)
Copyright Terracotta 2007

Open Source Clustering for Java
QueueReader
private static final class QueueReader implements Runnable {
private final NamedQueue myQueue;
public QueueReader(NamedQueue queue) {
this.myQueue = queue;
}
public void run() {
while (true) {
try {
System.out.println(new Date() + \": message from the \" + myQueue.getName()
+ \" queue: \" + myQueue.take());
} catch (InterruptedException e) {
// A real application would do something interesting with this
// exception.
e.printStackTrace();
}
}
}
Copyright Terracotta 2007

Open Source Clustering for Java
Queue Writer
//...
private void run() {
while (true) {
try {
String mood = MOODS[random.nextInt(MOODS.length)];
myQueue.add(myColor + \" says, \\\"I'm feeling \" + mood + \".\\\"\");
Thread.sleep(1000);
} catch (InterruptedException e) {
// A real application would do something with this exception
e.printStackTrace();
}
}
}
// ...
Copyright Terracotta 2007

Open Source Clustering for Java
CoordinationWithQueues Config File
...
<dso>
<instrumented-classes>
<include>
<class-expression>
org.terracotta.book.coordination.queues.CoordinationWithQueues
</class-expression>
</include>
<include>
<class-expression>
org.terracotta.book.coordination.queues.CoordinationWithQueues$NamedQueue
</class-expression>
</include>
</instrumented-classes>
<roots>
<root>
<field-name>org.terracotta.book.coordination.queues.CoordinationWithQueues.QUEUES</field-name>
</root>
<root>
<field-name>
org.terracotta.book.coordination.queues.CoordinationWithQueues.sharedCounter</field-name>
</root>
</roots>
<locks>
<autolock>
<method-expression>
void org.terracotta.book.coordination.queues.CoordinationWithQueues.main(java.lang.String[])
</method-expression>
<lock-level>write</lock-level>
</autolock>
</locks>
</dso>
...
Copyright Terracotta 2007

Case Studies
Copyright Terracotta 2007

Open Source Clustering for Java
Fast, Simple, Scalable
“ [T]hanks to Terracotta and your post about the message bus
you did we have stripped all J2EE out of our architecture
making it much simpler for service developers, much faster,
and much more scalable. What has us so excited about this
approach is exactly what you said about developer
productivity - that is Right On!
--http://blog.markturansky.com/archives/77
Copyright Terracotta 2007

Open Source Clustering for Java
Large Publisher Gets Caught Down the Path with Oracle
Scaling Out or Up?
Copyright Terracotta 2007

Open Source Clustering for Java
Breaking the Pattern without Leaving “Load-Balanced” World
• $1.5 Million DB & HW savings
• Doubled business
• More than halved database load
Copyright Terracotta 2007

Open Source Clustering for Java
Coming Soon: Examinator Reference Application
 Online test proctoring application  Fully tested & tuned
 Popular stack  Example architecture &
 Spring MVC, Webflow components
 Sitemesh  Example project layout and tools
 Freemarker integration (build/test/debug/
 Spring Security deploy)
 Tomcat/Jetty  Fully documented best practices
 JPA and recommended SDLC
 Hibernate processes
 MySQL
 Maven
 Junit
Copyright Terracotta 2007

Open Source Clustering for Java
Gnip—Internet Data Aggregation and Delivery Service
Copyright Terracotta 2007

Open Source Clustering for Java
Gnip—Internet Data Aggregation and Delivery Service
Copyright Terracotta 2007

Open Source Clustering for Java
Gnip—Internet Data Aggregation and Delivery Service
Initial Architechture
 JMS Queuing
 Backing Database
JMS JMS
Liabilities
 Many moving parts
 Many technologies
DB
 Increased developer specialization
 Lower core-competency density
Copyright Terracotta 2007

Open Source Clustering for Java
Gnip—Internet Data Aggregation and Delivery Service
Terracotta Architecture
 Natural, in-memory data structures
EC2 Node 1: TC Client EC2 Node 2: TC Client
 Durable, TC-backed objects
Periodic
EC2 Node 3: TC Server snapshot of
Terracotta
object store for
backup
S3 Backup
Copyright Terracotta 2007

Open Source Clustering for Java
Gnip—Internet Data Aggregation and Delivery Service
Performance
 50,000 messages/second
 3-4 EC2 nodes
EC2 Node 1: TC Client EC2 Node 2: TC Client
Benefits
 Fewer technologies, increased
core competency
Periodic
 App built w/ simple Java
EC2 Node 3: TC Server snapshot of
constructs
Terracotta
object store for
 Clustering and redundancy “just
backup
works”
S3 Backup
 Excellent monitoring/debugging
tools
 “I can’t believe you give them
away for free…”
Copyright Terracotta 2007

Open Source Clustering for Java
Common Use Patterns
Copyright Terracotta 2007

Open Source Clustering for Java
Community Resources
 http://www.terracotta.org/
 http://forums.terracotta.org/
 Mailing lists:
 tc-dev@terracotta.org
 tc-users@terracotta.org
 IRC:
 #terracotta channel on freenode
 Subversion
 http://svn.terracotta.org/svn/tc
 http://svn.terracotta.org/svn/forge
Copyright Terracotta 2007