Terracotta

Context Database abuse

Database used to store Durable and Temporary data

The database can become a bottleneck when too many requests

SPOB

SPOF

Goals

High availability

High performances

Linear scalability

A possible solution : data grids

It is a cluster of machines that handles in memory a large quantity of shared data

Terracotta (Server)

Clustering at the JVM level

1 active TC server

Server TC :Shared data

Clients list

Spread the updates

Manage locks

Garbage Collector

Terracotta (Client)

From the codeNo specific storage structure, only use Java classes

Recommanded to use "synchronized" keyword

Configuration file (XML)To configure the objects to share (roots)

To configure locks

To configure distributed methods

...

Useful for

Relieving Database OverloadDistributed Caching

Hibernate second level cache

HTTP Session

Simplifying Application Architecture and avoid clustering by handVirtual Heap for Large Datasets

Clustering OSS Frameworks

Master / Worker

POJO Clustering

Linear Scalability by connected JVMs

HTTP Sessions

Demo

Sample Terracotta application

Clustering a Wicket Application

Wicket stores objects into the sessionPage, PageMap...

These objects would need to be declared in the Terracotta configurationAlready done in a wicket-module for Terracotta

*..*

Gallery

Sharing Data

Wicket, as a Java application, will use objects for the business layer

Instead of coming from the database, those objects can be in memory

Should be declared in the tc-config file

Classes using it (Pages), should declare it in the tc-config file

public class SharedAlbum extends Observable implements Serializable { private List images;private String defaultImage;private String host;private String album;private boolean slideShow = false;}

Demo

Sharing information

Wicket application vs Swing client

Ajax component

Using of a checkbox to activate / deactivate a slideshow

Wicket has built in integration for Ajax behaviours

By clicking on the checkbox, The Album object state will be update on the server with the value of the checkboxThe update object is shared / clustered via Terracotta

add(new AjaxCheckBox("slideshow", new PropertyModel(this, "slideshow")) {

@Overrideprotected void onUpdate(AjaxRequestTarget target) {album.updateSlideShowStatus(slideshow);}});

Slideshow

Demo

Sharing information -Ajax checkbox

Why a cache ?Temporal Locality

Non-uniform distribution

EhCache

Hibernate 2nd level cache

Terracotta

Temporal Locality

Non Uniform Distribution

Non Uniform Distribution

top 4 pages account for >50% of total hitstop 17 pages account for >80% of total hits (14% of total pages)spend small amount of memory to cache top 14% of pages -> remove 80% of load

Cache limitations

Amdahl' LawIf the thing youre caching is not your bottleneck, it wont matter

Memorycache uses memory which your app might need

Concurrencyaccess to cache can be a bottleneck

Reduce LAtency

EhCache

First created in 2003 by Greg Luck

Most widely used Java cache

Apache 2.0 licence

JSR 107 Java cach implementation

EhCache Architecture

Hibernate 2nd Level Cache

Using Terracotta

EhCache 1.7.0 can be as drop in replacement

Side effect on a single node, keeping state

Monitoring and profiling capabilities

Distributed transparently

Using Terracotta

Enhancement to Hibernate

More efficient in-memory and total count eviction (3.1.1)

Better visibility of memory conditions

Improved Query Caching

Improved performance of core Terracotta (lock manager and memory manager)

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Zenika 2008