Idempotent Services
Idempotent
“adj. Acting as if used only once, even if used multiple times. This term is often used with respect to {C} header files, which contain common definitions and declarations to be included by several source files. If a header file is ever included twice during the same compilation (perhaps due to nested #include files), compilation errors can result unless the header file has protected itself against multiple inclusion; a header file so protected is said to be idempotent. The term can also be used to describe an initialization subroutine that is arranged to perform some critical action exactly once, even if the routine is called several times.”
“It is not always possible to determine when a server instance failed with respect to the work it was doing at the time of failure. For instance, if a server instance fails after handling a client request but before returning the response, there is no way to tell that the request was handled. A user that does not get a response retries, resulting in an additional request.
Failover for RMI objects requires that methods be idempotent. An idempotent method is one that can be repeated with no negative side-effects.”
I found a good discussion of making services idempotent and the reasons for doing so at RunOfTheMillBlog.
Posted on July 6th, 2004 under Work • 
• 
• RSS 2.0 feed • Both comments and pings are currently closed
