i have 10 users. and i want to set a cron for that 10 users. Now when a perticular user logged in he can set the corn time from his panel and cron will run at that time .Also when new user added a new cron will be set for that user with default time according to application.
how can i achieve this?
I agree with thomasmalt that it is not wise but what you should do instead is have it so your users can set a cron time in a 'users' database table (like mysql) with columns: 'interval (INT)' and 'last_update (DATETIME)'. So every user has their own time set. Then you decide what is the lowest increment you will allow (such as 1 minute) and only let your users set times higher than that.
Then you run a cron every 1 minute which checks the 'users' table. Find any users where interval is less than or equal to the time since 'last_update'. Then run your actions for those users. This effectively does the same thing as setting crons for every user.
This sounds generally like a very unwise thing to do, but if you know what you're doing and understand the security problems involved etc. I would suggest solving this using two scripts
one php part which lets the user view his crontab and manipulate time settings using an html form and storing the wanted changes in a known place on your system.
one shell script part running as a trusted user on your system picking up the changes at a given interval (once a minute maybe) and doing the actual updates to cron.
Adding stuff to cron is potentially a very dangerous thing and only very trusted users should be allowed to do so. Any web solution should be regarded as insecure and you should take extra care to make sure any input is properly audited.
As thomasmalt said this is probably not wise to do in a public system ... you don't want to let users mess with system crons.
I suggest you let the users specify a time of day in their controlpanel and have a cron script run every minute. In that script it's easy enough to fetch the users that match the current time and execute their script. It achieves the same thing, is a little more verbose and more to code but alot more secure.
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I'm working on a basic lamp(willing to change) website , and I currently need a way to run some function on the server that runs for several hours per user, and every X hours it needs to query the mysql database to see if the value for that user has been updated, if it hasn't it need it to insert a new record in the database...I also should mention that the 'every X hours' can change per user too, and the total runtime of the function per user can also vary.
So basically I need a function that runs continuously on the server for few hours per user. What is the best way to do this? I want the site to be able to support many users (like 10000 +).
I'm willing to try new technologies for every aspect of the site, I'm still in the design phase and I was looking for some input.
I've looked at cron but not really sure how well it would work when dealing with so many users...
edit: Here is a typical scenario of events;
User presses button on the website and closes the browser.
Server starts a timer from when they pressed the button, now
the server will check if that user has pressed a different button within a given time frame (time frame can change per user), say within 30 minutes. If they didn't press the other button then the server needs to automatically insert a new record in the database.
The script will need to continue running, checking every 30 mins for say the next 5 hours.
Thank you!
Cron would work as well as you can code the page it will run. It's not a cron limitation.
The question is ambiguous btw. Maybe explaining your full scenario would help.
Meanwhile, my suggestion would be to set up a scrip that allows you to manually check what you need to check.
You definitely need the DB to be InnoDB optimized with proper indexes to be able to support 1000 plus users.
To alleviate the number of calls to the database, a common practice is to run scripts only on what you are interested (so in the case of users you would only select those who have logged on in say the past 3 hours)
That's achievable in 2 ways, a simple select statement, or by adding entries to a specific table on the login page, and remove them after the automated script has finished running.
All of this is pure theory without understanding exactly what you need to do though.
You are telling what/how you want to do, but not why you want to do it. Maybe letting us know why could lead to a different how ;)
However, what you can do is still use cron (or anything similar). The trick is to have
a last_interaction timestamp column
a maximum_interval column
a daily_runtime column
in your users database. Not optimized but you are in the design phase so you shouldn't pay too much attention to the performance aspect (except is explicitly required).
I'm developing a web game (js php mysql) in which one clicks a button to start an action that takes time to complete (let's say 10 hours) and when it finishes some points are added to that player's total.. The problem is that I need those points to be added even if the player is not online at the time the action finishes.. for example I need to have the rankings updated, or an email sent to the player..
I thought about a cron job checking constantly for ending actions, but I think that would kill the resources (contantly checking against actions of thousands of players..).
Is there a better solution to this problem?
Thanks for your attention!!
You can just write into your database when it's finished and when the user logs in you add the earned points to his account. You can also check with a cronjob. Even if you have millions of user this will not kill your server.
Cron is perfect for this. You could write your tasks in stored procedures, then have cron run an SQL script to call the stored procedure that would update the records of your players.
Databases are designed to work with thousands and millions of pieces of information efficiently, so I don't think the idea that it will kill system resources is a valid one unless you hosting system is really constrained already.
If you want to be safe against cheating you need to do the checking on the server anyway. If the "waiting" will happen within a Javascript on the client, one could easily decrease the remaing time.
So you need to send the job to the server (which is assumed to be safe against clock modifications) and the server will determine the end timestamp. You could store your jobs in a queue.
If you only need this information for the user himself you can just look at the queue when the user logs in. Otherwise run a cron job every minute (or so). This job will mark all jobs finished when their timestamp is in the past (and remove them from the database).
If you need more precise checking you will need to come up with an alternative server side solution that is doing this more often (e.g. a simple program polling the database every few seconds).
I've search on the web and apparently there is no way to launch a php script without user interaction.
Few advisors recommend me Cron but I am not sure this is the right way to go.
I am building a website where auctions are possible just like ebay. And after an amount of time the objects are not available anymore and the auction is considered as finished.
I would like to know a way to interact with the database automatically.
When do you need to know if an object is available? -> Only if someone asks.
And then you have the user interaction you are searching for.
It's something different if you want to, let's say, send an email to the winner of an auction. In this case you'd need some timer set to the ending time of the auction. The easiest way to do this would be a cron job...
There are several ways to do this. Cron is a valid one of them and the one I would recommend if its available.
Another is to check before handling each request related to an object whether it is still valid. If it is not, you can delete it from the database on-the-fly (or do whatever you need to) and display a different page.
Also you could store the time at which your time-based script was run last in the database and compare that time with the current time. If the delay is large enough, you can run your time based code. However, this is prone to race conditions if multiple users hit the page at the same time, so the script may run multiple times (maybe this can be avoided using locks or anything though).
To edit cronjobs from the shell: crontab -e
A job to run every 10 minutes: */10 * * * * curl "http://example.com/finished.php"
TheGeekStuff.com cron Examples
Use heartbeat/bot implement
ation
Cron job that runs pretty frequently or a program that starts on boot and runs continuously (maybe sleeping periodically) is the way to go. With a cron job you'll need to make sure that you don't have two running at any given time or write it such that it doesn't matter if you have more than one working at any given time. With "resident" program you'll need to figure out how to handle the case when it crashes unexpectedly.
I wouldn't rely on this mechanism to actually close the auction, though. That should be handled in your database/web site. That is, the auction has a close time and either the database constraints or your code makes it impossible to bid on a closed auction. Notifying the winner and seller, setting up the payment process, etc. are things your service/scheduled task could do.
I have a database with a table and some columns. One of these columns is flags (similar to SO) where users can flag comments. I would like to give each user 5 flags per day. So if a user uses 2 flags in a 24 hour period, the flags should reset to 5 at the end of the 24 hours. I really have no idea how to do this. Is there a special mysql function?
PHP:
$query=mysql_query("UPDATE users SET flags='5' WHERE userID='$user'");
how would i get this to repeat every 24 hours? (if this is the right solution)
The best way is probably to set up an automated task (possibly using cron) that runs a query to do this.
Make a script and add to cron job. It will automatically update all on specified time of day.
Cron is very simply a Linux module that allows you to run commands at predetermined times or intervals. In Windows, it’s called Scheduled Tasks. The name Cron is in fact derived from the same word from which we get the word chronology, which means order of time.
Using Cron, a developer can automate such tasks as mailing ezines that might be better sent during an off-hour, automatically updating stats, or the regeneration of static pages from dynamic sources. Systems administrators and Web hosts might want to generate quota reports on their clients, complete automatic credit card billing, or similar tasks. Cron has something for everyone!
You can use MySQL Event Scheduler and define an event to let it update every interval you want.
I'm writing a realtime wep application, something similar to auction site. The problem is that I need a daemon script, preferrably php, that runs in background and constantly launches queries to mysql db and basing on some of criterias (time and conditions from resultsets) updates other tables. Performance of the daemon is crucial. Sample use case: we have a deal that is going to expire in 2:37 minutes. Even if nobody is watching/bidding it we need to expire it exactly in 2:37 since the time it started.
Can anybody advise a programming technology/software that performs this kind of task the best?
Thanks in advance
UPDATED: need to perform a query when a deal expires, no matter if it has ever been accessed by a user or not.
Why do you need to fire queries at time intervals? Can't you just change how your frontend works?
For example, in the "Deals" page, just show only deals that haven't expired - simplified example:
SELECT * FROM Deal WHERE NOW() <= DateTimeToExpire
Accordingly for the "Orders" page, a deal can become a placed order only if time hasn't expired yet.
Does your daemon need to trigger actions instantaneously? If you need a table containing the expired state as a column you could just compute the expire value on the fly or define a view? You could then use a daemon/cron job querying the view every 10 minutes or so if you have to send out emails or do some cleanup work etc.