Software Fault Tolerance in the Application Layer
Yennun Huang, Chandra M. R. Kintala · 1995
By software fault tolerance in the application layer, we mean a set of application level software components to detect and recover from faults that are not handled in the hardware or operating system layers of a computer system. We consider those faults that cause an application process to crash or hang; they include application software faults as well as faults in the underlying hardware and operating system layers if they are undetected in those layers. We define four levels of software fault tolerance based on availability and data consistency of an application in the presence of such faults. We describe three reusable software components that provide up to the third level of software fault tolerance. Those components perform automatic detection and restart of failed processes, periodic checkpointing and recovery of critical volatile data, and replication and synchronization of persistent data in an application software system. These components have been ported to a number of UNIX 2 platforms and can be used in any application with minimal programming effort. Some telecommunications products in AT&T have already been enhanced for faulttolerance capability using these three components. Experience with those products to date indicates that these modules provide efficient and economical means to increase the level of fault tolerance in a software system. The performance overhead due to these components depends on the level and varies from 0.1 % to 14 % based on the amount of critical data being checkpointed and replicated.