Hazelcast Introduction

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Introduction to Hazelcast
Sandeep Pandey

Motivative Data Structures behind Hazelcast development
[ Java Behind Hazelcast]
● HashMap
● ConcurrentHashMap
● Multicast Discovery Mechanisms
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HashMap
● Hashmap is Array of LinkedList.
● HashMap is best fit for Caching.
● HashMap has two very important function i.e. put(K,V) and get(K).
How put(K,V) and get(K) work?
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Node<K,V>
int hash;
K key ;
V value;
Node<K,V> next;

Concurrency in HashMap
HashMap is not thread safe
and throws
ConcurrentModificationException.
new MyThead(stores).start()
resulting
ConcurrentModificationException.
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ConcurrentHashMap (CHM)
● ConcurrentHashMap also have same functionality as HashMap,
except in case of multiple thread access instead object lock, Segment
gets lock.
● Map<K,V> stores= new ConcurrentHashMap<>(int initialCapacity, float
loadFactor, int concurrencyLevel);
● By default initialCapacity (n) equals to concurrencyLevel (cl), unless
we specify. n segment gets created and only particular segment get
lock for operating thread.
○ If n=16 and cl =8 , One lock per 2 segments.
○ If n=16 and cl=32, Two thread will manage one segment
○ CHM never throws CME.
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Discovery Mechanisms
● TCP/IP
○ List all or a subset of the members' hostnames and/or IP
addresses as cluster members.
● Multicast
○ Allows cluster members to find each other using multicast
communication.
This is not broadcasting!
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Problem with Current Infrastructure
● Traditional system has single Database and that leads to
Performance issue.
● We can resolve performance issue by introducing cache, but there are
cache consistency issues. Also there is no way recover data if system
fails before data persist to DB.
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Introducing Hazelcast
● Apache License
● Super light, simple, no-dependency (~7 MB Jar)
● Hazelcast cluster scales elastically
● Distributed/partitioned implementation of map, queue, set, list, lock
and executor service
● No Master, each member in the cluster configured to be functionally
same
● Build your own custom-distributed data structures using SPI.
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Introducing Hazelcast..
● User defined object must implement Serializable interface (by java
provided or Hazelcast provided), to store in Hazelcast node else
exception thrown at Runtime.
● Hazelcast is thread safe as ConcurrentHashmap.
● Hazelcast configuration can be controlled in declarative or
programmatic way.
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Hazelcast Architecture..
● Hazelcast is an In-Memory Data Grid.
● Hazelcast is extension of ConcurrentHashMap, here object shared
between multiple JVM’s.
● Discovery mechanisms being use to connect JVM’s (Node)
● Data stored in-memory (RAM) of the servers.since it is incredibly fast.
● Multiple copies are stored in multiple machines for automatic data
recovery in case of failures.
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Data Partitioning
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● Hazelcast stores data in partitions
● Default partition number is 271
● Backups partitions for redundancy
● Partition table
● Repartition
○ When member joins the cluster
○ When member leaves the cluster
● Partition can be increased, if data size
per partition is bigger than 100 Mb.
● pid = hash(convert key to byte []) % pc
(271) *pid: partitionId pc: partitionCount

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Hazelcast Topology
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Client/Server Embedded

Hazelcast use cases
● Highly available distributed cache for applications
● Publish/subscribe communication at highest speed and scalability
● An alternative to Coherence and Terracotta
● As storage for session data in web applications
● Parallel processing on multiple JVMs
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Hazelcast Demo
1. Caching
2. User Defined Object for caching
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Basic Configuration
1. Get Hazelcast specific object reference
Config cfg = new Config();
HazelcastInstance instance = Hazelcast.newHazelcastInstance(cfg);
Map<Integer, String> citesMap = instance.getMap("mapName");
2. Configuration
hazelcast.xml is default file used for configuration of node, password,
discovery mechanism etc.
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References:
http://docs.hazelcast.org/docs/latest-development/manual/html/index.ht
ml
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Hazelcast Introduction

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