Databases Reference
In-Depth Information
FIGURE 6.5: Different types of failures in message communication.
• Uniform semantics: Local and remote communications should imple-
ment similar primitives for data exchange.
• E
ciency: A good message-passing scheme minimizes the number of
messages communicated between processes. For e
ciency, some opti-
mization is typically adopted. For example, avoiding the cost of estab-
lishing and terminating connections between the same pair of processes
for each and every message exchange between them; minimizing the cost
of maintaining connections; and piggybacking the acknowledgment of a
previous message on the next message.
• Reliability: Message passing schemes must be able to handle lost and
duplicate messages. Fault tolerance and error control approaches should
be considered. There are three types of communication failures that
require full consideration by the message passing system developers:
lost request message, lost response message, and unsuccessful execution
of the request. Figure 6.5 illustrates each of these failures.
6.2.1.1
Message Passing Interface (MPI)
Message Passing Interface (MPI) is a set of specifications that details the
message passing libraries for developers and users. MPI by itself is not a li-
brary. It is the specification of what such a library should be. The goal of Mes-
sage Passing Interface is to provide a widely used standard for writing message
passing programs. The interface provides a practical, portable, e
cient, and
flexible standard for the development of message passing applications.
For the development of parallel programs, MPI offers a number of benefits:
standardization, portability, performance opportunities, enhanced functional-
ity, and different forms of availability. In the context of standardization, MPI is
the only message passing library considered to be a standard. It is supported
by all major platforms and many specialized high-performance computing
(HPC) systems. Practically, it has replaced all previous message passing li-
braries, such as OpenMP. Developers are not required to modify message
