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There are many approaches available to scale PostgreSQL beyond running on a single server. An outline of the terminology and basic technologies involved is at High Availability and Load Balancing. There is a presentation covering some of these solutions. There is no one-size fits all replication software. You have to understand your requirements and how various approaches fit into that. For example, here are two extremes in the replication problem space: You have a few servers connected to a local network you want to always keep current for failover and load-balancing purposes. Here you would be considering solutions that are synchronous, eager, and therefore conflict-free. Your users take a local copy of the database with them on laptops when they leave the office, make changes while they are away, and need to merge those with the main database when they return. Here you'd want an asynchronous, lazy replication approach, and will be forced to consider how to handle conflicts in cases where the same record has been modified both on the master server and on a local copy. These are both database replication problems, but the best way to solve them is very different. And as you can see from these examples, replication has a lot of specific terminology that you'll have to understand to figure out what class of solution makes sense for your requirements. A great source for this background is in the Postgres-R Terms and Definitions for Database Replication. The main theoretical topic it doesn't mention is how to resolve conflict resolution in lazy replication cases like the laptop situation, which involves voting and similar schemes.

"The Qt SOAP project provides basic web service support with version 1.1 of the SOAP protocol. The SOAP (Simple Object Access Protocol) component recognizes the XML standard for describing how to exchange messages. Its primary usage is to invoke web services and get responses from Qt-based applications. These classes make it easy to construct, send, receive and process SOAP messages on the client side."

"An "executable" UML model is one with a behavioral specification detailed enough that it can effectively be "run" as a program. This can be extremely valuable in order to test and validate the model, independently of the one or more implementation platforms to which the system being modeled will ultimately be deployed. Or, in some cases, the model itself can actually be run as the production implementation, given an appropriate execution environment. There have been model execution tools and environments for years, even before UML. However, each tool defined its own semantics for model execution, often including a proprietary action language, and models developed in one tool could not be interchanged with or interoperate with models developed in another tool. A previous post described Stephen Mellor's quest of more than a decade to change this through OMG standards for precise UML model execution semantics and a UML action language. In 2008, this led to the adoption of the Foundational UML (fUML) specification, providing the first precise operational and base semantics for a subset of UML encompassing most object-oriented and activity modeling. The fUML specification still did not provide any new concrete surface syntax, however, tying the precise semantics solely to the existing abstract syntax model of UML. This meant that, in order to fully specify a detailed behavior in a UML model - say the effect behavior of a transition on a state machine or the method of an operation of a class - one still had to draw a very detailed, graphical activity diagram. "

Caching is the most important performance optimization technique. There are many things that can be cached in persistence, objects, data, database connections, database statements, query results, meta-data, relationships, to name a few. Caching in object persistence normally refers to the caching of objects or their data. Caching also influences object identity, that is that if you read an object, then read the same object again you should get the identical object back (same reference). JPA 1.0 does not define a shared object cache, JPA providers can support a shared object cache or not, however most do. Caching in JPA is required with-in a transaction or within an extended persistence context to preserve object identity, but JPA does not require that caching be supported across transactions or persistence contexts. JPA 2.0 defines the concept of a shared cache. The @Cacheable annotation or cacheable XML attribute can be used to enable or disable caching on a class.

"JSwat is a graphical Java debugger front-end, written to use the Java Platform Debugger Architecture and based on the NetBeans Platform. JSwat is open-source software and is freely available in both binary and source code form. Its features include sophisticated breakpoints; colorized source code display with code navigator; byte code viewer; movable display panels showing threads, call stack, visible variables, and loaded classes; command interface for more advanced features; and Java-like expression evaluation, including method invocation. "

"OpenXava is a tool for Rapid Java Web Development, well-suited for business and database oriented applications. Write simple domain classes with Java or Groovy, and get an AJAX application ready for production. Since v4.2 OpenXava also produces iPad Web applications that behaves and looks like iPad native applications."

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Garbage Collection Interview Questions 117) What is Garbage Collection? Garbage collection is a process of reclaiming the runtime unused objects.It is performed for memory management. more details... 118) What is gc()? gc() is a daemon thread.gc() method is defined in System class that is used to send request to JVM to perform garbage collection.

Papyrus is aiming at providing an integrated and user-consumable environment for editing any kind of EMF model and particularly supporting UML and related modeling languages such as SysML and MARTE. Papyrus provides diagram editors for EMF-based modeling languages amongst them UML 2 and SysML and the glue required for integrating these editors (GMF-based or not) with other MBD and MDSD tools. Papyrus also offers a very advanced support of UML profiles that enables users to define editors for DSLs based on the UML 2 standard. The main feature of Papyrus regarding this latter point is a set of very powerful customization mechanisms which can be leveraged to create user-defined Papyrus perspectives and give it the same look and feel as a "pure" DSL editor.

"Scalaz is a library written in the Scala Programming Language. The intention of Scalaz is to include general functions that are not currently available in the core Scala API. The scalaz-core module depends only on the core Scala API and the core Java 2 Standard Edition API. Scalaz is released under a BSD open source licence making it compatible with the licence of the Scala project. Scalaz 6.0.1 was released in June 2011, targeting Scala 2.8.1 and 2.9.0.1. "

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