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| <document> | |
| <properties> | |
| <title>Web Grid</title> | |
| <author email='Sean.Kelly@jpl.nasa.gov'>Sean Kelly</author> | |
| </properties> | |
| <!-- Sirius Isness - Irrational Substance --> | |
| <body> | |
| <section name='Web Grid'> | |
| <p>The OODT <a href='/grid/'>grid services</a> | |
| (<a href='/grid-product/'>product</a> | |
| and <a href='/grid-profile/'>profile</a> services) use CORBA | |
| or RMI as their underlying network transport. However, | |
| limitations of CORBA and RMI make them inappropriate for | |
| large-scale deployments. For one, both are procedural | |
| mechanisms, providing a remote interface that resembles a | |
| method call. This makes streaming of data from a service | |
| impossible, because there are limitations to the sizes of data | |
| structures that can be passed over a remote method call. | |
| Instead, repeated calls must be made to retrieve each block of | |
| a product, making transfer speeds horribly slow compared to | |
| HTTP or FTP. (Block-based retrieval of profiles was never | |
| implemented, resulting in out of memory conditions for large | |
| profile results, which is another problem.) | |
| </p> | |
| <p>Second, both CORBA and RMI rely on a central name registry. | |
| The registry makes an object independent of its network | |
| location, enabling a client to call it by name (looking up its | |
| last known location in the registry). However, this requires | |
| that server objects be able to make outbound network calls to | |
| the registry (through any outbound firewall), and that the | |
| registry accept those registrations (through any inbound | |
| firewall). This required administrative action at | |
| institutions hosting server objects and at the institution | |
| hosting the registry. Often, these firewall exceptions would | |
| change without notice as system adminstrators changed at each | |
| location (apparently firewall exceptions are poorly documented | |
| everywhere). | |
| </p> | |
| <p>Further, in the two major deployments of OODT (PDS and EDRN), | |
| server objects have almost never moved, nullifying any benefit | |
| of the registry. This project, OODT Web Grid, avoids the | |
| prolems of CORBA and RMI by using HTTP as the transport | |
| mechanism for products and profiles. Further, it provides a | |
| password-protected mechanism to add new sets of product and | |
| profile query handlers, enabling seamless activation of | |
| additional capabilities. | |
| </p> | |
| </section> | |
| <section name='Documentation'> | |
| <p>Further documentation on Web Grid is forthcoming. In the | |
| mean time, check out these <a href='./slides.pdf'>presentation | |
| slides</a>. (Don't worry, they're not in PowerPoint format.) | |
| </p> | |
| </section> | |
| </body> | |
| </document> |