software engineering Software engineering is a branch of both computer science and engineering focused on designing, developing, testing, and maintaining Application software, software applications. It involves applying engineering design process, engineering principl ...

, software aging is the tendency for

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

to fail or cause a system failure after running continuously for a certain time, or because of ongoing changes in systems surrounding the software. Software aging has several causes, including the inability of old software to adapt to changing needs or changing technology platforms, and the tendency of

software patch Software consists of computer programs that instruct the execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital computers in the mid-20th cen ...

es to introduce further errors. As the software gets older it becomes less well-suited to its purpose and will eventually stop functioning as it should. Rebooting or reinstalling the software can act as a short-term fix. A proactive fault management method to deal with the software aging incident is software rejuvenation. This method can be classified as an environment diversity technique that usually is implemented through software rejuvenation agents (SRA). The phenomenon was first identified by

David Parnas David Lorge Parnas (born February 10, 1941) is a Canadian early pioneer of software engineering, who developed the concept of information hiding in modular programming, which is an important element of object-oriented programming today. He is al ...

, in an essay that explored what to do about it:

"Programs, like people, get old. We can't prevent aging, but we can understand its causes, take steps to limit its effects, temporarily reverse some of the damage it has caused, and prepare for the day when the software is no longer viable."

From both an academic and industrial point of view, the software aging phenomenon has increased. Recent research has focussed on clarifying its causes and effects. Memory bloating and

leaking A leak is a way (usually an opening) for fluid to escape a container or fluid-containing system, such as a Water tank, tank or a Ship, ship's Hull (watercraft), hull, through which the contents of the container can escape or outside matter can e ...

, along with

data corruption Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data. Computer, transmission, and storage systems use a number of meas ...

and unreleased file-locks are particular causes of software aging.

Proactive management of software aging

Software aging

Software failures are a more likely cause of unplanned systems outages compared to hardware failures. This is because software exhibits over time an increasing failure rate due to data corruption, numerical error accumulation and unlimited resource consumption. In widely used and specialized software, a common action to clear a problem is rebooting because aging occurs due to the complexity of software which is never free of errors. It is almost impossible to fully verify that a piece of software is bug-free. Even high-profile software such as

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

and

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

must receive continual updates to improve performance and fix bugs. Software development tends to be driven by the need to meet release deadlines rather than to ensure long-term reliability. Designing software that can be immune to aging is difficult. Not all software will age at the same rate as some users use the system more intensively than others.

Rejuvenation

To prevent crashes or degradation, software rejuvenation can be employed proactively as inevitable aging leads to failures in software systems. This proactive technique was identified as a cost-effective solution during research at the

AT&T Bell Laboratories Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...

on fault-tolerant software in the 1990s. Software rejuvenation works by removing accumulated error conditions and freeing up system resources, for example by flushing operating system kernel tables, using garbage collection, reinitializing internal data structures, and perhaps the most well known rejuvenation method is to reboot the system. There are simple techniques and complex techniques to achieve rejuvenation. The method most individuals are familiar with is the hardware or software

reboot In computing, rebooting is the process by which a running computer system is restarted, either intentionally or unintentionally. Reboots can be either a cold reboot (alternatively known as a hard reboot) in which the power to the system is physi ...

. A more technical example would be the

web server A web server is computer software and underlying Computer hardware, hardware that accepts requests via Hypertext Transfer Protocol, HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, co ...

software Apache's rejuvenation method.

Apache The Apache ( ) are several Southern Athabaskan language-speaking peoples of the Southwestern United States, Southwest, the Southern Plains and Northern Mexico. They are linguistically related to the Navajo. They migrated from the Athabascan ho ...

implements one form of rejuvenation by killing and recreating processes after serving a certain number of requests. Another technique is to restart

virtual machine In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...

s running in a

cloud computing Cloud computing is "a paradigm for enabling network access to a scalable and elastic pool of shareable physical or virtual resources with self-service provisioning and administration on-demand," according to International Organization for ...

environment. The multinational telecommunications corporation

AT&T AT&T Inc., an abbreviation for its predecessor's former name, the American Telephone and Telegraph Company, is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the w ...

has implemented software rejuvenation in the real time system collecting billing data in the United States for most telephone exchanges. Some systems which have employed software rejuvenation methods include: # Transaction processing systems # Web servers # Spacecraft systems The

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an American 501(c)(3) organization, 501(c)(3) public charity professional organization for electrical engineering, electronics engineering, and other related disciplines. The IEEE ...

International Symposium on Software Reliability Engineering (ISSRE) hosted the 5th annual International Workshop on Software Aging and Rejuvenation
woSAR
in 2013. Topics included: * Design, implementation, and evaluation of rejuvenation mechanisms * Modeling, analysis, and implementation of rejuvenation scheduling * Software rejuvenation

benchmarking Benchmarking is the practice of comparing business processes and performance metrics to industry bests and best practices from other companies. Dimensions typically measured are Project management triangle, quality, time and cost. Benchmarking is ...

Memory leaks

Some

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

s, like C and C++, allow the programmer to allocate

heap memory Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynam ...

. Moreover, the programmer may be required to free the memory when the memory is no longer needed. Freeing the memory is necessary because some

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s (OS) don't perform

garbage collection Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of treatment or landfill. Waste collection also includes the curbside collection of recyclable ...

when a

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...

finishes. Over time, this is likely to consume more and more memory, eventually causing the computer to run out of memory. In low memory conditions, the computer usually functions slower due to intense swapping and thrashing. When this happens, applications become sluggish or even unresponsive. If the computer runs out of both memory and swap space, the OS might automatically reboot — or even worse hang. Programs written in programming languages that use a garbage collector (e.g.

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

) are less prone to memory leaks, since memory that is no longer referenced will be freed up by the garbage collector. This however does not mean it's impossible to write code that leaks memory in such languages. Sometimes critical components of the OS itself can be a source of memory leaks. In

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

, for example, the memory use of a

Windows Explorer File Explorer, previously known as Windows Explorer, is a file manager application and default desktop environment that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user i ...

plug-in might drain the available memory to the point of making the entire computer unusable. A

might be needed.

Implementation

Two methods for implementing rejuvenation are: # Time based rejuvenation # Prediction based rejuvenation

Memory bloating

Garbage collection is a form of automatic

memory management Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of Resource management (computing), resource management applied to computer memory. The essential requirement of memory manag ...

whereby the system automatically recovers unused memory. For example, the .NET Framework manages the allocation and release of memory for software running under it. But automatically tracking these objects takes time and is not perfect. .NET based web services manage several logical types of memory such as stack, unmanaged and managed heap (free space). As the physical memory gets full, the OS writes rarely used parts of it to disk, so that it can reallocate it to another application, a process known as paging or swapping. But if the memory does need to be used, it must be reloaded from disk. If several applications are all making large demands, the OS can spend much of its time merely moving data between main memory and disk, a process known as disk thrashing. Since the garbage collector has to examine all of the allocations to decide which are in use, it may exacerbate this thrashing. As a result, extensive swapping can lead to garbage collection cycles extended from milliseconds to tens of seconds. This results in usability problems.

Proactive management of software aging

Software aging

Rejuvenation

Memory leaks

Implementation

Memory bloating

See also

References

Further reading