Sign In

Communications of the ACM

Practice

The Network Is Reliable


The Network Is Reliable, illustration

Credit: Dalibor Zivotic

back to top 

"The network is reliable" tops Peter Deutsch's classic list of "Eight fallacies of distributed computing," all [of which] "prove to be false in the long run and all [of which] cause big trouble and painful learning experiences" (https://blogs.oracle.com/jag/resource/Fallacies.html). Accounting for and understanding the implications of network behavior is key to designing robust distributed programs—in fact, six of Deutsch's "fallacies" directly pertain to limitations on networked communications. This should be unsurprising: the ability (and often requirement) to communicate over a shared channel is a defining characteristic of distributed programs, and many of the key results in the field pertain to the possibility and impossibility of performing distributed computations under particular sets of network conditions.

For example, the celebrated FLP impossibility result9 demonstrates the inability to guarantee consensus in an asynchronous network (that is, one facing indefinite communication partitions between processes) with one faulty process. This means that, in the presence of unreliable (untimely) message delivery, basic operations such as modifying the set of machines in a cluster (that is, maintaining group membership, as systems such as Zookeeper are tasked with today) are not guaranteed to complete in the event of both network asynchrony and individual server failures. Related results describe the inability to guarantee the progress of serializable transactions,7 linearizable reads/writes,11 and a variety of useful, programmer-friendly guarantees under adverse conditions.3 The implications of these results are not simply academic: these impossibility results have motivated a proliferation of systems and designs offering a range of alternative guarantees in the event of network failures.5 However, under a friendlier, more reliable network that guarantees timely message delivery, FLP and many of these related results no longer hold:8 by making stronger guarantees about network behavior, we can circumvent the programmability implications of these impossibility proofs.


 

No entries found

Log in to Read the Full Article

Sign In

Sign in using your ACM Web Account username and password to access premium content if you are an ACM member, Communications subscriber or Digital Library subscriber.

Need Access?

Please select one of the options below for access to premium content and features.

Create a Web Account

If you are already an ACM member, Communications subscriber, or Digital Library subscriber, please set up a web account to access premium content on this site.

Join the ACM

Become a member to take full advantage of ACM's outstanding computing information resources, networking opportunities, and other benefits.
  

Subscribe to Communications of the ACM Magazine

Get full access to 50+ years of CACM content and receive the print version of the magazine monthly.

Purchase the Article

Non-members can purchase this article or a copy of the magazine in which it appears.