Notes from the November 14 NovaJUG meeting

Enterprise-class Java applications by clustering the JVM with Terracotta

Of all tech meetings I attend, NovaJUG’s are the most difficult for me to follow. I have decided just to reproduce my notes from the presentation. I hope my programmer readers will find them useful.

Ari Zilka presented on Terracotta’s clustering technology. Some highlights:

- Zilka said he believes Terracotta is the first to use transparent clustering at a high level.

- Clustering is not about shared memory

- Terracotta’s code is free, it is supported by a subscription service.

- cluster is above Java Virtual Machine and below the application

- clustering in runtime offers more control

- Terracotta 2.2 is due for release on December 4

Here Zilka made a demonstration of Terracotta with two Macs where two users moved images/objects on the screen simultaneously.

Zilka made some general observations about Java technology:

- Java specification is good; Java uses a strict & valuable set of semantics

Concerning Java serialization:
- language should work the way we were taught in the book
- object identity and pass-by reference
- coordination between threads

- return same reference to same object: map dot put = map dot get

- with serialization objects are moved across applications, you lose trust

- Terracotta clusters at runtime

- stateless programming - because operators can shut down neatly

- load balancing is good; but balancing at application level consistently is best

- with Terracotta you can write to stateful and run in statelessness

- managed runtimes relieve developers (example, memory management)

- Why runtime management is better, you can see patterns of activity, example, who accesses what information and how often they access it

- Terracotta put (serialization) get (deserialization)

- serialization perturbs the domain model

How API based clustering impacts simplicity
-scale out solutions relay on Java serialization
- perturbs the domain model
- adds new coding rules

Locality of reference
- database object not local for processor
- if an object can move then one must map
- must be able to lock object

Terracotta
- handles the getting and putting in the map
- you can trust equality
- no API
- almost no code

Terracotta instrumentation
- map level memory, read/write operations
- network based clustering with consistency
- transparent to business logic

- Bytecode instrumentation

AOP style control; does anyone have this object before I create it and if so, what is the address?

- no peer to peer in Terracotta

- Control cluster server knows who has the lock

- clustering to the heap

Capabilities
- heap level replication - share object
- ACID Replicators - no new exception or error scenarios
- central storage - keeps application state across restarts
- communications hub - manage shared objects
- virtual memory
- coordination

- stateful applications/stateless server

- Terracotta saves each field of each object

- JBoss is not ACID compliant; Terracotta is

- Terracotta shell servlets invoke Java for you

- stateless - kill any node - and still pick up where I left off

- logical extension of your heap

- Hub & Spoke -> scale the hub
- field level changes -> batched
- network overload -> runtime optimized

- Terracotta should be used with Hotspot 1.4 or 1.5, it works with Tomcat, WebLogic, Spring, and Weflow