Timed events with php/MySQL

Question

I need a way to modify a value in a table after a certain amount of time has passed. My current method is as follow:

insert end time for wait period in table
when a user loads a page requesting the value to be changed, check to see if current >= end time
if it is, change the value and remove the end time field, if it isn't, do nothing

This is going to be a major feature on the site, and so efficiency is the key; with that in mind, you can probably see the problem with how I'm doing it. That same chunk of code is going to be called every time someone access a page that needs the information.

Any suggestions for improvements or better methods would be greatly appreciated, preferably in php or perl.

In response to cron job answers: Thanks, and I'd like to do something like that if possible, but hosts limits are the problem. Since this is a major part of the app, it can't be limited.

What sort of timespan are you looking at? updating after a few seconds would be easy, updating after a few hours, more difficult. — Marc Gear
– Marc Gear, Commented Sep 23, 2008 at 19:20
on a shared host, that's about the best you can do. If this is a major enough application that efficiency of this method is in question, you need a better host. You can get an affordable VPS that will give you root access and that you can run cron on as frequently as you like. — Aeon
– Aeon, Commented Sep 23, 2008 at 20:03

Owen · Accepted Answer · 2008-09-23 18:48:13Z

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why not use a cron to update this information behind the scenes? that way you offload the checks on each page hit, and can actually schedule the timing to meet your app's requirements.

answered Sep 23, 2008 at 18:48

Owen

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Overbeeke · Accepted Answer · 2008-09-23 19:47:22Z

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Your solution sounds very logical, since you don't have access to cron. Another way could be storing the value in a file, and the next time the page is loaded check when it was last modified (filemtime("checkfile.txt")), and decide if it needs modifying again. You should test performance for both methods.

answered Sep 23, 2008 at 19:47

Overbeeke

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MattBelanger · Accepted Answer · 2008-09-23 18:48:11Z

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Can you use a cron job to check each field in the database periodically and update that way?

A big part of this is how frequently the updates are required. A lot of shared hosts limit the frequency of cron checks, for example no more than every 15 minutes, which could affect the application.

answered Sep 23, 2008 at 18:48

MattBelanger

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Joe Phillips · Accepted Answer · 2008-09-23 21:16:48Z

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You could use a trigger of some sort on each page load. I really have no idea how that would affect performance but maybe somebody else can shed some light.

answered Sep 23, 2008 at 21:16

Joe Phillips

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DGM · Accepted Answer · 2008-09-23 21:12:27Z

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If performance really starts to be an issue, (which means a lot more than you probably realize) you could use memchached to store the info...

answered Sep 23, 2008 at 21:12

DGM

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