Database Reference
In-Depth Information
or memory-to-memory transfers. When disk is utilized as a data source (or
destination), it is usually the disk that is the bottleneck in the system. For
memory-to-memory transfers we see that the end hosts, and the eciency of
application and protocol implementations, are becoming the bottleneck. In
addition to the main memory optimization, multiple remote resources (data
servers) may be utilized in parallel to improve data transfer performance.
4.4.5 Challenges and Future Directions
With increasing availability of high-speed wide area network connections we
expect the amount of interest in high-speed transfer protocols to increase.
Although a significant number of transport protocols have been proposed,
the availability of implementations for the end user is still very limited. We
believe that the problem of finding ecient transport mechanism for appli-
cations will continue to be a dicult one in the near future. The need for
developing new protocols and analyzing the existing ones will continue to in-
crease as new requirements are formulated and new applications are emerging.
Ecient implementations will be needed for these protocols to be adopted. A
framework for evaluating transport protocols as well as frameworks for imple-
menting new transport protocols will help with some of the issues. We believe
that in the future different applications will use different transport protocols.
Also a single application will use different protocols when executed in differ-
ent network environments. Defining a set of application benchmarks and a set
of representative network environments may help protocol designers in the
future.
4.5 Remote Input and Output
An alternate form of access to distant data is remote I/O, where the files
of interest stay in one place, and the programs issue network operations
to read or write small amounts of data that are of immediate interest. In
this model, transfer protocols must be optimized for small operations, and
the processing site may need no storage at all. Figure 4.4 shows both of
these modes of file access. There are several potential benefits for employing
remote I/O:
Remote I/O simplifies usability.
It is not always easy for the end
user to identify exactly what files he or she needs. A complex program
or dataset can easily consist of hundreds of files and directories, of which
not all are needed for any given task. In an interactive application, it
may not even be possible to identify the needed files until runtime. When
using remote I/O, the system fetches the files needed at runtime, and
the user is freed from this burden.
