The fallacies of distributed computing are a set of assertions made by L Peter Deutsch and others at Sun Microsystems describing false assumptions that programmers new to distributed applications invariably make. These result either in the failure of the system, a substantial reduction in system scope, or in large, unplanned expenses required to redesign the system to meet its original goals.
Contents
The fallacies
The fallacies are:
- The network is reliable.
- Latency is zero.
- Bandwidth is infinite.
- The network is secure.
- Topology doesn't change.
- There is one administrator.
- Transport cost is zero.
- The network is homogeneous.
The effects of the fallacies
- Software applications are written with little error-handling on networking errors. During a network outage, such applications may stall or infinitely wait for an answer packet, permanently consuming memory or other resources. When the failed network becomes available, those applications may also fail to retry any stalled operations or require a (manual) restart.
- Ignorance of network latency, and of the packet loss it can cause, induces application- and transport-layer developers to allow unbounded traffic, greatly increasing dropped packets and wasting bandwidth.
- Ignorance of bandwidth limits on the part of traffic senders can result in bottlenecks over frequency-multiplexed media.
- Complacency regarding network security results in being blindsided by malicious users and programs that continually adapt to security measures.
- Changes in network topology can have effects on both bandwidth and latency issues, and therefore similar problems.
- Multiple administrators, as with subnets for rival companies, may institute conflicting policies of which senders of network traffic must be aware in order to complete their desired paths.
- The "hidden" costs of building and maintaining a network or subnet are non-negligible and must consequently be noted in budgets to avoid vast shortfalls.
- If a system assumes a homogeneous network, then it can lead to the same problems that result from the first three fallacies.
History
The list of fallacies generally came about at Sun Microsystems. L. Peter Deutsch, one of the original Sun "Fellows", is credited with penning the first seven fallacies in 1994; however, Bill Joy and Tom Lyon had already identified the first four as "The Fallacies of Networked Computing" (the article claims "Dave Lyon", but this is a mistake). Around 1997, James Gosling, another Sun Fellow and the inventor of Java, added the eighth fallacy.