Lightstreamer Server Moderato A scalable and reliable server for pushing live data to Rich Internet Applications
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Lightstreamer Server Moderato Description

A scalable and reliable server for pushing live data to Rich Internet Applications Lightstreamer Server Moderato is based on the Comet paradigm and it will stream real-time data to any Web browser, without installing anything on the client. HTML, AJAX, Flex, AIR, Silverlight clients, as well as Java, .NET, iPhone applications, can receive live data from Lightstreamer.Lightstreamer has been used in many mission-critical production systems, where scalability, low network impact, bandwidth management, adaptive streaming, and other advanced features, have proven fundamental. Here are some key features of "Lightstreamer Server Moderato": Very High Scalability: · Lightstreamer Server is a very scalable system, based on a staged event-driven architecture and asynchronous I/O. TCP-Level Optimization: · Lightstreamer has direct control over the composition of the TCP packets. Instead of delegating the aggregation of data in packets to the operating system using the Nagle algorithm, Lightstreamer Server itself decides on each occasion the optimum composition of each TCP packet, with the objective/trade-off of reducing the delay time before data is dispatched as well as minimizing the number of dispatched packets. True Push/Streaming: · True push/streaming means that the data are sent by the server to the client in an asynchronous fashion. It is not up to the client to poll the server to know if new data is available (except for when Stream-Sense switches to Smart Polling). Stream-Sense and Smart Polling: · If a client is connected through a network infrastructure that blocks any form of streaming, then Lightstreamer is able to send the updates via a smart polling mode. The Web Client of Lightstreamer automatically detects if streaming is not supported (through the Stream-Sense feature) and in this case it switches to smart polling mode. AJAX Zero-Client Support: · Lightstreamer makes it possible to stream real-time data to a Web application that is purely based HTML and JavaScript, with no software installations and downloads (no applets, no plug-ins, etc.). Many AJAX frameworks and toolkits can take advantage of Lightstreamer to dynamically update their view. Authentication and Fine-Grained User Permissioning: · Lightstreamer supports user authentication and implements a very fine-grained permissioning policy so that any user’s action can be validated through the custom Metadata Adapter. Max Frequency per Item (updates/second): · The maximum allowed update frequency for each subscribed item, expressed as updates per second. For example, with the Presto Edition, in which such limit is 3, a session can subscribe to an arbitrary number of items (each item comprises a set of fields that get updated in real-time, e.g. a stock quote). For each item, the maximum update frequency of its set of fields is 3 updates per second. So 3 updates per second is not the maximum update frequency of a whole page, but just of each individual item contained in the page. More formally, the 3 update-per-second limitation can be expressed like this: two consecutive updates for a certain item are always delivered at a minimum distance of 333 milliseconds, where each update can contain information for an arbitrary number of fields for that item. Max Concurrent Users: · The maximum number of concurrent users (sessions) allowed by the Server. Variable means that it depends on the license type. Site Licenses limit the number of concurrent users based on the user packs that have been purchased. Per-Server Licenses do not directly limit the number of concurrent users but the number of server instances (and indirectly the number of users, based on the hardware capacity and application load). Frequency Control: · A maximum update frequency can be allocated for each user/item combination. For example, it is possible to configure the profile of a certain user so that they do not receive more than 2 updates per second for a certain subscribed item (piece of data). Adaptive Streaming and Congestion Control: · Lightstreamer automatically detects situations of congestion on the Internet, heuristically slowing down or suspending the dispatch of data until the connection is again fully serviceable. Heuristic Frequency Management for Web Clients: · The Lightstreamer Web Client libraries (used to develop HTML clients) contain heuristic algorithms that control the push frequency based on the CPU usage of the client. If the client is very slow because its CPU is dedicated to other tasks, the push frequency will be reduced accordingly. Pre-Filtering: · The pre-filter stage receives the data from the Data Adapter and lowers its frequency before the Kernel processes it and dispatches it to the clients at the final frequency. Filtering the data with two stages (stage 1: general filtering; stage 2: per-user filtering) greatly improves the performance. Multiple Subscription Modes (MERGE, DISTINCT, COMMAND, RAW): · Depending on the nature of the data and the type of application and client, different subscription modes can be chosen to select the most appropriate filtering algorithms. For more details about MERGE, DISTINCT, COMMAND and RAW modes please refer to the White Paper or to Lightstreamer documentation. Selector Mechanism, Event Customization, Backward Communication: · For each update of each subscribed item destined to each user, a selector can be applied to decide whether to send the update or discard it. Through the selector mechanism, the same item can be subscribed by different users with different views. · For each update of each subscribed item destined to each user, a transformation of the values can be applied through custom code before delivering the event to the client. · Clients can directly send messages to the Lightstreamer Metadata Adapter. Support for Unicode Data Push: · Unicode characters can be pushed from the Server to the Clients. Server Installation As a Stand-Alone Process: · Lightstreamer Server is a stand-alone process, which does not rely on web servers or application servers. This approach was taken in order to have direct control over the operating system's TCP/IP stack and to optimize the data transmission. Flexible Adapter-Based Server Integration: · By writing custom Adapters, Lightstreamer Server can be integrated with any kind of back-end system. A Data Adapter connects Lightstreamer to some data feed. A Metadata Adapter connects Lightstreamer to some authentication/authorization system. Multiple Data Adapter Support: · Each Lightstreamer Client session can access an Adapter Set, which comprises one Metadata Adapter and multiple Data Adapters. Basic HTML Monitoring Console: · An HTML page embedded in Lightstreamer Server that displays real-time data about the Server’s status. Push Export of Server Statistics: · The real-time Server status data available through the HTML Monitoring Console are available for subscription by any custom clients too. Requirements: · Java 2 Standard Edition Runtime Environment What's New in This Release: · Improved the logging of unexpected exceptions. · Introduced verbose notifications for exceptions thrown by Adapter methods. · Added logging for updates lost upon unfiltered subscriptions (which include RAW mode and ADD/DELETE in COMMAND mode). · Suppressed the "Unexpected empty selected list", "Unexpected empty read on a readable socket" and "Unexpected empty write on a writable socket" warnings for not significant cases.

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