Andes: a Scalable persistent Messaging System Charith Wickramarachchi, Srinath Perera, Shammi Jayasinghe,Sanjiva Weerawarana WSO2 Inc. http://www.flickr.com/photos/magnusvk/334474531/
Outline Dimensions of Scale Distributed Message Brokers Andes Architecture Distributed Pub/sub architecture Distributed Queues architecture Evaluation Conclusionphoto by John Trainoron Flickr http://www.flickr.com/photos/trainor/2902023575/, Licensed under CC
Message Brokers (e.g. JMS. AMQP)• A broker sits in the middle• Users send messages and receive them based on interests (asynchronous)• Publish/Subscribe (Topic) – deliver to all• Distributed Queues (Queue) – deliver to one, store and deliver, persistent
Messaging Systems in Real World • Event Based Systems – Sensor Networks – System Monitoring • CEP (Complex Event Processing) • Social Networks • Real time Analytics • Job queues/ schedulinghttp://www.flickr.com/photos/imuttoo/4257813689/ by Ian Muttoo, http://www.flickr.com/photos/eastcapital/4554220770/, http://www.flickr.com/photos/patdavid/4619331472/ by Pat David copyright CC
Challenges in Modern Message Oriented Middleware Why? Advances in technology areas like cloud computing and the increase of Internet based user bases demands for scalable message oriented middleware. Challenges High Availability Persistence Scale (Dimensions of scale) Number of messages Number of Queues Size of messages Current Messaging systems only scale in the first two http://www.artelista.com/ypobra.php?o=19550 dimensions
Distributed Message Brokers Single broker node cannot scale up Often messaging systems scale by a network of brokers where users can subscribe or publish (both to queues or topics) at any node. There are many algorithms and routing rules (e.g. NaradaBrokering , Gryphon , Oracle Advanced Queuing , TIBCO Rendezvous , IBM WebSphere MQ , and Padres ) Still doing ordered delivery with queues is a challenge
Cassandra and Zookeeper• Cassandra – NoSQL Highly scalable new data model (column family) – Highly scalable (multiple Nodes), available and no Single Point of Failure. – SQL like query language (from 0.8) and support search through secondary indexes (well no JOINs, Group By etc. ..). – Tunable consistency and replication – Very high write throughput and good read throughput. It is pretty fast.• Zookeeper – Scalable, fault tolerant distributed coordination framework
Alternative Message Broker Design• Most persistent message brokers use a per-node DB to store messages with message routing.• But with large messages, cost of routing messages over the network is very high• With availability of scalable storage and distributed coordination middleware we propose an alternative architecture for scalable message brokers• Main idea – Avoid message routing – Use scalable storage to share messages between nodes – Use distributed coordination to control the behavior
Andes – Overview Each node polls the queues for subscriptions assigned to itself Andes stores message content separately Delivery logic works with messages IDs written to queue representation in Cassandra and it only reads the messages at delivery
Andes – Overview (Contd.) Users can publish or subscribe to any node, and Andes delivers messages to all as if subscribe and publish operations are done in the same node. When published, each node writes the message to Cassandra There are nodes assigned to handle each queue/ topics, and they read messages from Cassandra and send them to subscribers Use Apache Zookeeper for coordination when needed Support for AMQP JMS and WS-Eventing while enabling interoperability between protocols Built by extending Apache Qpid Code base
Publish/Subscribe design (Contd.)• There is a queue representation implemented on Cassandra• Andes creates a queues for each subscription• When a broker receives a published message, it stores the message in a message store in Cassandra.• Broker will write message ids of relevant messages to the relevant subscriber queues based on the subscribed topic.• Each node polls Cassandra queue for subscriptions done at that node and delivers them to the subscribers.• Messages are deleted from Subscription queues after acknowledgement, and Andes deletes messages from the message store after a timeout.
Distributed Queues• Strict ordering means there can be one messages being delivered at a give time. – Say we receive messages m1, m2 for Queue Q. – Say we deliver messages m1 and m2 to client c1 and c2 for Queue Q in parallel – Say m1->c1 failed, but by then m2->c2 is done. – If there is no other subscribers, now m1 has to be delivered out of order.• Two implementation – Strict ordering support - using a distributed shared lock with Zookeeper – Best effort implementation
Test Setup• Test 1: Comparison with other Brokers – Single Broker Node – Changed the size of messages with different brokers (with 40 publishers) – Measured the throughput from subscribers for each case after sending 10,000 messages.• Test 2: Scalability test – Multiple brokers – 20 subscribers on the same queue – Changed the number of publishers – Measured the throughput from subscribers for each case after sending 10,000 messages.
Comparison with Other Brokers• Andes does much better than Qpid• Andes does better than HornetMQ for large messages
Initial Scalability Results• Adding more nodes improves throughput• But more concurrency deteriorate the results (need more work)
How does it Make a difference?• Scale up in all 3 dimensions• Create only one copy of message while delivery• High Availability and Fault Tolerance• File transfers in pub/sub (asynchronous style)• Let users choose between strict and best effort messages• Replication of stored messages in the storage
Conclusion and Future Work• Provides an alternative architecture for scalable message brokers using Cassandra and Zookeeper• It provides – A publish/subscribe model that does not need any coordination between broker nodes – A strict mode for distributed queues that provides in order delivery – A best-effort mode for distributed queue• Future work – Further Scalability Tests – Testing with large messages – Fault Tolerance Tests• Available as open source project under apache License.
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