Re: Update view of database on multiple web clients

On Tue, 28 Feb 2006 11:13:47 GMT, David Segall <david@xxxxxxxxxxx>
wrote, quoted or indirectly quoted someone who said :

Does the above sound as though it could work? Do you have a better
idea? Is there are a "standard" way of doing this? TIA

You are going to need some smarts in the client to handle this without
driving your users insane, e.g. Applet or JAWS.

The Applet either has to poll for things if finds of interest with a
request of the form"if X has changed since T, please send a copy.".
The problem here is slow response.

or the server has to send them unrequested when it determines that
info is of interest to that client. The server then maintains the
state of what he client SHOULD have, which of course may not match
what it DOES have. The problems here are fragility and complexity. You
can create a huge amount of server disk I/O obsessively tracking who
is currently looking at which bytes in the database.

A third approach is a combination. The server sends short "this
information has changed" invalidation notices to any client vaguely
interested (who may or may not have the item in its cache). The
client background thread marks it invalid in their caches, and may or
may not request an update. The advantage of this approach is you don't
have to micro manage what each client is caching from the server; you
need keep only a rough idea what they want to be notified of. A
background thread in each Applet does most of the work of state
tracking.

The third approach is how the CSL School system worked, giving high
performance on klunky hardware.
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.
.

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