System prevalence [1] is a simple software architectural pattern that combines system images (snapshots) and transaction journaling to provide speed, performance scalability, transparent persistence and transparent live mirroring of computer system state.
In a prevalent system, state is kept in memory in native format, all transactions are journaled and System images are regularly saved to disk.
System images and transaction journals can be stored in language-specific serialization format for speed or in portable formats for cross-language consumption.
The first usage of the term and generic, publicly available implementation of a system prevalence layer was Prevayler, written for Java by Klaus Wuestefeld in 2001. [2]
Simply keeping system state in RAM in its normal, natural, language-specific format is orders of magnitude faster and more programmer-friendly than the multiple conversions that are needed when it is stored and retrieved from a DBMS. As an example, Martin Fowler describes "The LMAX Architecture" [3] with a transaction-journal and system-image (snapshot) based business system at its core, which can process 6 million transactions per second on a single thread.
A prevalent system needs enough memory to hold its entire state in RAM (the "prevalent hypothesis"). Prevalence advocates claim this is continuously alleviated by decreasing RAM prices, and the fact that many business databases are small enough already to fit in memory.
Programmers need skill in working with business state natively in RAM, rather than using explicit API calls for storage and queries for retrieval.
The system's events must be capturable for journaling.
In computing, serialization is the process of translating a data structure or object state into a format that can be stored or transmitted and reconstructed later. When the resulting series of bits is reread according to the serialization format, it can be used to create a semantically identical clone of the original object. For many complex objects, such as those that make extensive use of references, this process is not straightforward. Serialization of object-oriented objects does not include any of their associated methods with which they were previously linked.
Jakarta Enterprise Beans is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component that encapsulates business logic of an application. An EJB web container provides a runtime environment for web related software components, including computer security, Java servlet lifecycle management, transaction processing, and other web services. The EJB specification is a subset of the Java EE specification.
The Jakarta Transactions, one of the Jakarta EE APIs, enables distributed transactions to be done across multiple X/Open XA resources in a Java environment. JTA was a specification developed under the Java Community Process as JSR 907. JTA provides for:
The Common Object Request Broker Architecture (CORBA) is a standard defined by the Object Management Group (OMG) designed to facilitate the communication of systems that are deployed on diverse platforms. CORBA enables collaboration between systems on different operating systems, programming languages, and computing hardware. CORBA uses an object-oriented model although the systems that use the CORBA do not have to be object-oriented. CORBA is an example of the distributed object paradigm.
In computer programming, event-driven programming is a programming paradigm in which the flow of the program is determined by external events. Typical event can be UI events from mice, keyboards, touchpads and touchscreens, or external sensor inputs, or be programmatically generated from other programs or threads, or network events.
In software engineering, a software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into source or machine code. Rather, it is a description or template for how to solve a problem that can be used in many different situations. Design patterns are formalized best practices that the programmer can use to solve common problems when designing an application or system.
In computer science, a lock or mutex is a synchronization primitive that prevents state from being modified or accessed by multiple threads of execution at once. Locks enforce mutual exclusion concurrency control policies, and with a variety of possible methods there exist multiple unique implementations for different applications.
IBM CICS is a family of mixed-language application servers that provide online transaction management and connectivity for applications on IBM mainframe systems under z/OS and z/VSE.
In computer science, distributed shared memory (DSM) is a form of memory architecture where physically separated memories can be addressed as a single shared address space. The term "shared" does not mean that there is a single centralized memory, but that the address space is shared—i.e., the same physical address on two processors refers to the same location in memory. Distributed global address space (DGAS), is a similar term for a wide class of software and hardware implementations, in which each node of a cluster has access to shared memory in addition to each node's private memory.
In computer science, software transactional memory (STM) is a concurrency control mechanism analogous to database transactions for controlling access to shared memory in concurrent computing. It is an alternative to lock-based synchronization. STM is a strategy implemented in software, rather than as a hardware component. A transaction in this context occurs when a piece of code executes a series of reads and writes to shared memory. These reads and writes logically occur at a single instant in time; intermediate states are not visible to other (successful) transactions. The idea of providing hardware support for transactions originated in a 1986 paper by Tom Knight. The idea was popularized by Maurice Herlihy and J. Eliot B. Moss. In 1995, Nir Shavit and Dan Touitou extended this idea to software-only transactional memory (STM). Since 2005, STM has been the focus of intense research and support for practical implementations is growing.
In software engineering, a plain old Java object (POJO) is an ordinary Java object, not bound by any special restriction. The term was coined by Martin Fowler, Rebecca Parsons and Josh MacKenzie in September 2000:
"We wondered why people were so against using regular objects in their systems and concluded that it was because simple objects lacked a fancy name. So we gave them one, and it's caught on very nicely."
Java Card is a software technology that allows Java-based applications (applets) to be run securely on smart cards and more generally on similar secure small memory footprint devices which are called "secure elements" (SE). Today, a secure element is not limited to its smart cards and other removable cryptographic tokens form factors; embedded SEs soldered onto a device board and new security designs embedded into general purpose chips are also widely used. Java Card addresses this hardware fragmentation and specificities while retaining code portability brought forward by Java.
The Zope Object Database (ZODB) is an object-oriented database for transparently and persistently storing Python objects. It is included as part of the Zope web application server, but can also be used independently of Zope.
In computer science and engineering, transactional memory attempts to simplify concurrent programming by allowing a group of load and store instructions to execute in an atomic way. It is a concurrency control mechanism analogous to database transactions for controlling access to shared memory in concurrent computing. Transactional memory systems provide high-level abstraction as an alternative to low-level thread synchronization. This abstraction allows for coordination between concurrent reads and writes of shared data in parallel systems.
The anemic domain model is described as a programming anti-pattern where the domain objects contain little or no business logic like validations, calculations, rules, and so forth. The business logic is thus baked into the architecture of the program itself, making refactoring and maintenance more difficult and time-consuming.
In computer science, persistence refers to the characteristic of state of a system that outlives the process that created it. This is achieved in practice by storing the state as data in computer data storage. Programs have to transfer data to and from storage devices and have to provide mappings from the native programming-language data structures to the storage device data structures.
Prevayler is an open-source (BSD) system-prevalence layer for Java: it transparently persists plain old Java objects. It is an in-RAM database backed by snapshots of the system via object serialization, which are loaded after a system crash to restore state. Changes to data happen via transaction operations on objects made from serializable classes. Prevayler's development was started by Klaus Wuestefeld.
Component Object Model (COM) is a binary-interface standard for software components introduced by Microsoft in 1993. It is used to enable inter-process communication (IPC) object creation in a large range of programming languages. COM is the basis for several other Microsoft technologies and frameworks, including OLE, OLE Automation, Browser Helper Object, ActiveX, COM+, DCOM, the Windows shell, DirectX, UMDF and Windows Runtime.
InfinityDB is an all-Java embedded database engine and client/server DBMS with an extended java.util.concurrent.ConcurrentNavigableMap interface that is deployed in handheld devices, on servers, on workstations, and in distributed settings. The design is based on a proprietary lockless, concurrent, B-tree architecture that enables client programmers to reach high levels of performance without risk of failures.
Phantom OS is an orthogonally persistent managed code general-purpose operating system. It is based on a concept of persistent virtual memory, and executes bytecode in a virtual machine. It is one of a few OSes not based on classic concepts of Unix-like systems. Phantom is based on the principle that "Everything is an object", in contrast to the Unix-like approach of "Everything is a file".
{{cite web}}
: CS1 maint: multiple names: authors list (link)A thread that will process 6 million orders per second using commodity hardware.