NYCPHP Meetup

[Jesse Callaway]

On Wed, Mar 4, 2009 at 1:07 PM, David Mintz <vtbludgeon at gmail.com> wrote:
>
> On Wed, Mar 4, 2009 at 12:17 PM, John Campbell <jcampbell1 at gmail.com> wrote:
>>
>> >> Use AJAX instead to refresh just the part of the page that needs
>> >> refreshing. If it's a fair chunk of information, you set a "version"
>> >> on the server so the AJAX call just checks the current version vs it's
>> >> version. If it's different, then you refresh the content. If it's not
>> >> different, no need to refresh anything and you only did a light weight
>> >> server call, so you could do it every 15 seconds.
>> >
>> > Forgive me, I don't quite understand *how* you would set the version
>> > information on the server in order to compare.
>>
>> In many cases, you can get away with using timestamps.  If you have
>> update_at columns, then you can compare the timestamps.  In theory,
>> there are problems with this method (such as updates that happen
>> during the same second), but in practice, it works quite well.
>
>
> Still not sure I get it -- I am competing the for Slowest Mind of the Year
> Award.
>
> The users are looking at a set of database rows. The table does have
> last-modified and creation-datetime columns. Saving the current set's
> maximum last-update and/or created value in the client, and then checking
> against the server by running an Ajax request to a server-side script that
> in turn queries the db to see if anything has changed... seems like almost
> as much overhead as just reloading unconditionally. Indeed more in those
> instances where you query to check if something changed, then do another
> query to load the data because something did change.
>
> And by "change" I mean in the dataset they are looking at, a row may have
> been either created, updated or deleted since they last loaded the view. So
> last-modified values would not inform you about deletions.
>
> I don't understand the md5() technique either. I mean, I know about md5()
> but don't see how you would use it efficiently for this purpose.
>
> --
> David Mintz
> http://davidmintz.org/
>
> The subtle source is clear and bright
> The tributary streams flow through the darkness
>
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Get a hash of the data returned from your remote request and remember
it at the client. If you choose you can remember it on the server-side
as well. But you might not have control over that, say if you are
grabbing the weather from a provider.
Anyway next time you get a response back check it against the
remembered md5. If there's a match then don't update the document. I
don't know if it's efficient or not, but it would cut down on
redrawing the screen.

-jesse