Patent Application
20050210109
The present invention relates to the field of data processing and more specifically to a mechanism for load balancing message consumption across multiple topic subscribers in a publish/subscribe broker messaging system.
Distributed applications have begun to proliferate, as have a host of previously unexplored problems associated with message synchronization, transmission reliability, system scalability, and message security. Present solutions include conventional messaging systems formed from loosely coupled components communicating with one another with asynchronous messages. Notably, conventional messaging systems have been used to build highly reliable, scalable, and flexible distributed applications.
At its core, the conventional messaging system permits separate, uncoupled applications to reliably communicate in an asynchronous manner. Importantly, the messaging system architecture generally replaces the client/server model with a peer-to-peer relationship between individual computing components, wherein each peer computing component can send and receive messages to and from other peer computing components. In consequence, messaging systems can provide several significant advantages over other, more conventional distributed computing models.
For instance, messaging systems encourage “loose coupling” between message consumers and message producers. Specifically, there exists a high degree of anonymity between producer and consumer. In fact, from the perspective of the message consumer, it does not matter who produced the message, where the producer resided in the computing network, and when the message had been produced. As a result, dynamic, reliable, and flexible systems can be assembled whereby entire ensembles of sub-applications can be modified without affecting the remaining portion of the system. In any event, conventional messaging systems assume one of two messaging system models: publish/subscribe and point-to-point.
The publish/subscribe messaging system supports an event driven model where consumers and producers participate in the transmission of messages. A topic represents messages with a common theme. Consumers interested in receiving a theme's messages “subscribe” to the topic. Producers wishing to transmit messages concerning a theme “publish” those messages to the topic. More particularly, producers associate messages with a specific topic, and the messaging system routes messages to consumers based upon the topics for which consumers have registered. When a message is published on a topic, each subscriber receives the message so that every subscriber receives a copy of every message. In point-to-point messaging systems, by comparison, each message is routed to an individual consumer so that even if there are multiple eligible consumers, each message is only consumed by one of the consumers (sometimes referred to as “competing consumers”).
Publish/subscribe broker systems have commonly been integrated into multi-function message broker systems which are used to inter-connect applications which may be on heterogeneous platforms and may use different message formats. For example, Tibco Software Inc. of Palo Alto, Calif. (USA) (www.tibco.com) has such a message broker called “TIB/Message Broker” (both “TIB” and “TIB/Message Broker” are trademarks of Tibco). In these multi-function message brokers, a set of pluggable data processing nodes is provided, with each node being dedicated to a specific data processing task, such as message format transformation, publish/subscribe message distribution, and a dispatcher for deciding (based on a plurality of predefined rules) where an incoming message should be routed.
In these multi-function message broker products, when a subscriber application registers a subscription request with the broker, the subscriber application sends the subscription request to a publish/subscribe broker node specifying the topic of the desired subscription. The publish/subscribe broker node (usually in cooperation with a plurality of other such publish/subscribe broker nodes) then ensures that any published messages on that topic are sent to the subscriber application.
The Java™ Message Service (JMS) API specification, part of the Java 2 Enterprise Edition (J2EE™) platform specification authored by Sun Microsystems of Santa Clara, Calif. (USA), provides standard APIs that Java developers can use to access the common features of enterprise messaging systems. JMS supports both the publish/subscribe and point-to-point models and allows the creation of message types consisting of arbitrary Java objects, arbitrary textural data formats, and arbitrary binary data formats. A fundamental design goal of JMS is to provide a consistent set of interfaces that messaging system clients can use independent of the underlying message system provider. In this way, not only are client applications portable across machine architectures and operating systems, but the client applications also remain portable across messaging products.
Still, in JMS, a messaging system subscriber is single threaded. As a consequence, even when a topic contains multiple messages, a single thread can only process the messages sequentially. Sequential processing limits throughput. For example, given that a topic can have multiple subscribers, and that a Java virtual machine is multithreaded, an application can have multiple subscribers on the same topic with each subscriber running in its own thread. Yet these multiple subscribers do not increase throughput, because the topic simply creates copies of each message for every subscriber. Increasing the number of subscribers increases the number of messages such that no increase in throughput occurs because each subscriber receives each message, and each subscriber must process each message.
What is needed is a system to distribute the work of consuming messages from a message channel (e.g., queues/topics/destinations in WebSphere MQ, Tibco, Microsoft Message Queuing, etc.) across multiple consumers so that the processing effort of the consumers can benefit from load balancing, failover, and other advantages that would be made possible by a distribution across multiple consumers. Multiple consumers dividing up messages on a point-to-point channel (e.g., queue) is not a problem. As discussed above, in a point-to-point messaging system, each message is only consumed by one consumer out of a group of multiple eligible consumers. However, messages cannot be divided up in this manner on a publish/subscribe channel (e.g., topic), because adding more subscribers to a topic only creates more copies of the messages, and each subscriber receives a copy of each message. Thus load cannot be distributed across multiple topic subscribers on a publish/subscribe channel the way it can across multiple queue consumers on a point-to-point channel.
With current messaging system implementations, each topic subscriber gets its own unique subscription. What is needed is an enhanced publish/subscribe messaging system where multiple subscribers can share a single subscription, and a published message would only be delivered to one of the subscribers sharing the subscription. In such an enhanced publish/subscribe messaging system, the messaging system's topic, rather than creating a copy of each published message for every subscriber, would then create a single copy for each subscription. When multiple subscribers share a subscription, a subscription dispatcher would deliver a particular message to only one of the subscribers sharing the subscription. The subscription dispatcher could be configured in a number of ways to achieve load balancing, to provide for failover, and to achieve other advantages.
The present invention is a messaging system which overcomes the deficiencies of the prior art and provides a novel and non-obvious system and method for load balancing a publish/subscribe messaging system comprising a topic subscription program, a publication program, and a message delivery program. The topic subscription program allows a subscriber to subscribe to a topic, and to share a subscription to that topic with other subscribers within the subscription. The publication program publishes messages to a topic. The message delivery program sends a copy of a message to each subscription and chooses the subscriber within the subscription to receive the message in accordance with a subscription dispatcher. A messaging system which has been configured in accordance with one aspect of the present invention can include a message server; one or more topics stored in the message server; one or more subscriptions associated with at least one of the topics in the message server; and, a subscription program, a publication program, and a message delivery program in the server.
There are shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:
As used herein, the term “computer” shall mean a machine having a processor, a memory, and an operating system, capable of interaction with a user or other computer, and shall include without limitation desktop computers, notebook computers, tablet computers, personal digital assistants (PDAs), servers, handheld computers, and similar devices.
As used herein, the term “computer program” shall mean any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form.
As used herein, the term “enhanced publish/subscribe message system” shall mean a computer implemented network of publishers and subscribers providing a one-to-many notification system where a message published by a sender is only received by one subscriber within a subscription and the decision as to which subscriber within a subscription is to receive the message is made by a message delivery program that either contains, or has the capability to invoke, a subscription dispatcher.
As used herein, the term “failover” shall mean automatically and transparently redirecting requests from a primary database, server or network to an alternate database, server or network if the primary database, server or network fails or is shut down.
As used herein, the term “load balancing” shall mean distributing the load of processing messages at a subscriber by having a message delivery program distribute the messages for a subscription to the subscribers sharing the subscription, such that any one message for a subscription will only be processed by a single subscriber and the decision as to which subscriber within the subscription will receive a message is made by the message delivery program.
As used herein, the term “message” shall mean precisely formatted data that is produced and consumed by applications and may represent a request, report, or an event.
As used herein, the term “message delivery program” shall mean a program having a subscription dispatcher for determining which subscribers sharing a subscription shall receive a particular message.
As used herein the term “messaging system” shall mean a computer network that provides asynchronous communication between applications that communicate by sending and receiving messages.
As used herein, the term “publish/subscribe message system” shall mean a computer implemented network of publishers and subscribers providing a one-to-many notification system where a message published by a sender is received by all subscribers, where subscribers specify which notifications are of interest by subscribing to a topic for that interest, and where publishers notify interested subscribers by publishing to the topic for that interest.
As used herein, the term “subscription dispatcher” shall mean a software mechanism for deciding which subscriber will receive a message where a plurality of subscribers are sharing a subscription and only one subscriber can receive each message: the software mechanism may vary in complexity from an algorithm providing an arbitrary distribution to a rules engine, and may further comprise a capability to automatically alter the algorithm or the rules engine in response to data received by monitoring subscriber activity.
As used herein, the term “topic” shall mean an intermediate address for messages conforming to a common interest that keeps message publishers independent of subscribers, and vice versa and that automatically adapts to changes in both publishers and subscribers.
As used herein, the term “publisher” shall mean the part of a computer program that sends messages to a topic.
As used herein, the term “subscriber” shall mean the part of a computer program that receives messages from a topic wherein the subscriber expresses interest in a topic by subscribing to it and then has a subscription to the topic so that it will receive messages sent to that topic.
As used herein, the term “subscription” shall mean a record of a subscriber's interest in receiving the messages published on a topic.
The internal configuration of a computer, including connection and orientation of the processor, memory, and input/output devices, is well known in the art. The present invention is a methodology that can be embodied in a computer program. Referring to
In alternative embodiments, SP 500, PP 600, and MDP 700 can be stored in the memory of other computers. Storing SP 500, PP 600, and MDP 700 in the memory of other computers allows the processor workload to be distributed across a plurality of processors instead of a single processor. Further configurations of SP 500, PP 600, and MDP 700 across various memories are known by persons of ordinary skill in the art. The present invention may be a method, a stand alone computer program, or a plug-in to an existing computer program. For computer programs such as those described herein, persons of ordinary skill in the art are aware of how to configure the programs to plug into an existing computer program.
The distribution by subscription can be accomplished in a variety of ways. In JMS, a subscriber is created by invoking the method:
When a message is published on a topic, the messaging system normally creates a copy for each subscriber. Now, the messaging system will create a copy for each subscription. If a subscription has multiple subscribers, only one subscriber will receive each message, and the decision as to which subscriber receives which message made will be made by the subscription dispatcher in the message delivery program. A subscriber can still ensure that it receives a copy of every message published by ensuring that it is the only subscriber on its subscription, which it can do by making sure its subscription ID is secret, or perhaps by specifying to the topic that its subscription cannot be shared with other subscribers.
Both durable and nondurable subscribers can share a subscription. If a subscription has all nondurable subscribers, the subscription survives as long as any of them remain connected; when they all disconnect, the subscription ends. If a subscription has at least one durable subscriber, the subscription does not end until all of the durable subscribers unsubscribe and all of the nondurable subscribers disconnect.
Persons skilled in the art are aware of numerous ways in which to make decisions regarding which subscriber will receive which message in the enhanced publish/subscribe message system 400. The subscription dispatcher may be included within the Message Delivery Program, or it can reside separately where it can be invoked by the Message Delivery Program. The subscription dispatcher can be as simple as an algorithm or as complex as a rules engine. An algorithm can merely dispatch messages in an arbitrary fashion or it may be more complex. A rules engine may vary in complexity depending on the needs of the designer. The subscription dispatcher enables load balancing to be provided in a system that otherwise would not be able to have such a feature. Even in a very simple form, such as sending one message to the first subscriber, the next message to the next subscriber and so on, the fact that each subscriber now only has to process a portion of the total messages sent from a topic has decreased the processing load for that subscriber. Moreover, the subscription dispatcher may be modified by a system administrator so as to achieve a load balancing distribution in accordance with the needs of that system administrator. Also, the subscription dispatcher can provide failover. For example, if a subscriber's server, network or database fails, the messages will be allocated among the remaining subscribers. Additionally, the subscription dispatcher may be modified by observing behavior aspects of the subscribers within the message distribution system. In other words, a wide variety of load balancing methods are therefore enabled. Since only one message is sent to each subscriber within a subscription, the receiving subscriber only has to process the data from the messages it receives, rather than all of the messages to the topic.
The present invention can be realized in hardware, software, or a combination of hardware and software. An implementation of the method and system of the present invention can be realized in a centralized fashion in one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system, or other apparatus adapted for carrying out the methods described herein, is suited to perform the functions described herein.
A typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein. The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which, when loaded in a computer system is able to carry out these methods.
Those skilled in the art will appreciate that such computer readable instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Further, such instructions may be stored using any memory technology, present or future, including but not limited to, semiconductor, magnetic, or optical, or transmitted using any communications technology, present or future, including but not limited to optical, infrared, or microwave. It is contemplated that such a computer program product may be distributed as a removable media with accompanying printed or electronic documentation, e.g., shrink wrapped software, pre-loaded with a computer system, e.g., on a system ROM or fixed disk, or distributed from a server or electronic bulletin board over a network, e.g., the Internet or World Wide Web.
Significantly, this invention can be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.
