Suppose a database server - say MySQL, though I'd be interested in
answers to my question for other systems too - and client are separated
by a low bandwidth link such as DSL, and the client repeatedly issues a
query for, say, a current product list.

Suppose the product list is large, but only a handful of entries have
typically changed between queries. It would be nice if only the changes
from last query to current one could be sent, saving bandwidth.

Is there any way to do this?

Thanks,

--
"Always look on the bright side of life."
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Yes there is but you are going to have to keep track of the items in
the list that have not changed since the last query. More
specifically, you will need to keep track of the time the last query
was made and also the time an item in the product list was last
updated. The client would have to cache the results of the query as
well.

On Feb 14, 10:29 am, Russell Wallace <russell.no.s... (AT) gmail (DOT) com>
wrote:
There's always a way. The question is at what cost.

You could reprogram the client side to buffer entries and change the
query to only request the changes (maybe via a timestamped
LAST_UPDATED/EFFECTIVE attribute). Only the client knows what it has,
so the burden is on that side.

So the costs:
DB changes for the list
Server changes (need to set that timestamp) in the source list
client changes (need to select using that timestamp)

HTH
ed