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Posted by C. on 09/17/07 13:31
On 16 Sep, 18:48, Jerry Stuckle <jstuck...@attglobal.net> wrote:
> FrobinRobin wrote:
> > Hi I need to create a list that is updated whenever a change occurs in
> > the database.
> > I first used Ajax to poll a part of the page and query the database
> > every 5-10 seconds, downloading the data every time... however as
> > someone pointed out.. polling is bad practice and uses a lot of
> > bandwidth.
>
> > I've given it some thought and I'm wondering whether I can use polling
> > more efficiently?
>
> > For example:
> > I have a function that querys the database and returns my results in a
> > structured array - I assign this as $current_list.
> > Then I poll a page that querys the database every 5-10 seconds and
> > compares $current_list against $new_list ... if there is a difference,
> > then it refreshes the $current_list array :)
>
> > As I'm refreshing the array on the server side and only downloading
> > when there is a change this should be much more bandwidth friendly
> > right?
>
> > Is there any point in only updating the part of the array which has
> > changed it's fairly small data (The array will have a max of ten
> > records (sub arrays) with 6 fields in each)
>
> > Many Thanks
>
> Downloading one row vs. 10 rows is probably an insignificant amount of
> overhead compared to the polling involved (unless your database is
> updated a lot).
>
> Personally, I'd be looking at a different way of doing it - for
> instance, a java applet. HTTP just isn't a good match for this type of
> operation.
Pushing from server to client will break in a lot of scenarios. If you
control the infrastructure in between then you'll know if it will
work.
It may be cheaper to measure the change from a different direction
(e.g. mod time on the database file, triggers on the tables...)
C.
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