I have this scenario:
an Asp.net/c# website with a rss reader/parser and a database. I would like to update the rss every x hours and save the new records in a database.
The indications I am receiving are that I need a dedicated server and a scheduler. I am not an expert about Asp but knowing that the server has a system time, it is natural to me thinking about using a timer.
I see that there is a timer in Asp.
Would it be possible to use a timer properly wrapped in the code, to get the functionality of the above scenario?
Yes you could use a timer inside a class (static or something that always has an instance activated) to accomplish this. One thing you are going to have to watch out for is that App Pools by default timeout and shutdown after 20 minutes of inactivity so you will want to change the settings to make it constantly run or make sure that something sends a request to the server every so often to keep the App Pool alive.
Related
Hello i'm trying to make an asp web application that send SMS to registered users whenever they receive an email , I'm a beginner when it comes to coding so I can't think of a pratique way to make it do that.
I thought of adding a timer and making it check every 5 minutes in the sql database for every user if there was something new but this will make the application slow assuming we have hundred of users.
I also thought of adding a trigger in the database and having it do the work but I can't find how to use sql trigger in visual studio, any Ideas that could help me ?
Thank you.
I thought of adding a timer and making it check every 5 minutes in the sql
database for every user if there was something new but this will make
the application slow assuming we have hundred of users ,
Why? Because I do not see that. Except slow means an average delay of 2.5 minutes. Then check every minute. Average delay down to 30 seconds.
I also thought of adding a trigger in the database and having it do the work but
I can't find how to use an sql trigger in visual studio , any Ideas that could
help me ?
Finding triggers? LEARN YOUR TOOLS. Seriously. But I personally would fire anyone using a trigger to then call an external program to send the SMS - the database is NOT where you want this.
Want it fast? Use a trigger to write a message to message broker (in sql server, it is a subsystem you likely do not know about because of not reading the documentation).
Have your app having some threads wait for messages there. There IS a special syntax to wait until a message arrives.
Voila, case closed.
May I suggest that you split up your code, put a message on a queue with the recipient and content of the SMS, and then create a separate webjob/service that subsbcribes to that queue and sends SMS whenever there is an entry there.
This gives you a clean separation of concerns, and removes the need to do polling to the database.
A couple of queues that are nice and easy to get started with:
Azure Storage Queue
Azure Service Bus Queue
I have written a web application in asp.net. It has some user roles. There are 3 roles which are Manager, Accountant and Employee. The employees write their expenses in a form and send it to Manager. When manager approves it, it'll be sent to Accountant to pay it. I need to have an idea that when manager doesn't approve the employee's expense in 48 hours, it should send an automatic e-mail to Manager's mail.
I thought that I can write another small console application to handle that by checking every hour. But it would waste resources and decrease performance.
I need a good idea to handle that. How should I do?
There are several options, but if I were you I would go with first or second options.
Console App & scheduler
I would create that console application that every time is run perform the check for you.
Then I will have it run using Windows Scheduler in a daily basis (at 00:05) or a hourly basis if you prefer so. This way Windows Scheduler daemon will launch it every hour and the rest of the time your app is not running.
Check this Microsoft link to see how a scheduled task is created in windows.
Restful Web Service & scheduler
As suggested in #marapet answer, having a restful web service that allow you to perform this action instead of a console application would give you the advantage of having all code in your web application.
Similar as previous one, you should only invoke the restful uri to have your action done. As possible disadvantage, you have to get sure that that uri is not accessible to end users. In usual architecture (Web Server --> Application Server --> DB) this restful service should be in the Application Servers, far away from end user access.
Windows Service
Another option is creating a Windows Service that runs all the time and check the time itself so every hour perform the job (maybe using Quartz or similar). But this does not meet your performance requirements.
The performance hit will be small anyway as your service should check every minute to see if an hour has pass and is time to do its job.. a task pretty easy.
The advantage is that a windows service is easier to control and monitor than a Scheduled tasks
DB job
Yet another option... If your app uses SQL Server you can have a t-sql job that runs daily or hourly. I wouldn't recommend this option unless you really have performance problems.
The problem with this is that you would be splitting the logic and responsibilities of your code. A future developer or admin would find hard to maintain your app.
If you'd like to keep the logic within the web application for simplicity (depending on the total size of your solution, this may or may not be desired):
For a given URL, have the web app check for due approvals and sends emails out if needed. Be sure to keep track of emails sent in order to prevent sending the same email multiple times.
Call this URL in a regular interval. You may use a scheduled task or a third party url monitoring service to do this.
You may call the URL with a simple VBScript (or wget, or curl, or powershell, or whatever is fastest for you), which in turn you can automate by using the task scheduler (see also).
An example script in vbscript for calling an URL:
Function LoadUrl(url)
Dim objRequest
Set objRequest = CreateObject("MSXML2.ServerXMLHTTP.6.0")
objRequest.open "POST", url , false
objRequest.Send
LoadUrl = objRequest.responseText
Set objRequest = Nothing
End Function
Checking every hour won't affect performance. Even checking every minute is probably fine, depending on your database. The simplest option is a console program fired as a Scheduled Task. You can also try a Windows Service but they're a bit trickier.
Also give some thought how you'll count the 48 hours. If an employee puts in expenses just before the weekend then 48 hours will probably elapse every time and you'll end up with a manager having lots of emails in their Inbox on Monday morning. That could cause some friction :)
I'm designing an ASP.NET 4.0 Web application where administrators may create an auction with an expiration. The expiration time would be stored in a database. How can I ensure that the auction ends at the predetermined time, considering the fact that an application instance may not be running when it is time? The application will be hosted with IIS7. I am considering Windows service, but I am wondering what other options are out there.
You can choose from two scenarios here:
Lazy with the web application
Active with a service
Lazy Scenario
Unless you have to interact instantly with the winner of an auction you could wait until the application starts and then let the application determine if there are any auctions that are expired. Collect them at that moment and handle them accordingly.
Active Scenario
Create a service that picks the first expiring auction from the DB. Store that DateTime and let the service sleep till the auction expires. Raise the service at that DateTime and process the expiring auction. Then let the service look for the next auction(s) to expire and let the service sleep again. And on and on.. I think The Windows Workflow Foundation contains all tools and requirements for this practice.
Something in between
Activate a scheduler that wakes up you web-app every hour/half hour/15 minutes and do the lazy stuff. Use a scheduler like HostMonitor.
A windows service that handles the timed events would be the best practice. Using a System.Threading.Timer in ASP.NET is bad juju; it MIGHT work in your case, because the change being made doesn't affect the UI directly, but I wouldn't bet on it working flawlessly. If you need to schedule events in the background of a web app, use a server app.
One thing to keep in mind; you may have hundreds or thousands of open auctions at a time. If you set a timer on every auction when it's opened, you'll have hundreds or thousands of sleeping threads managed by this server. I'd look only for auctions that would end before the next time you'd normally poll, and set timers for those auctions only. That would get you down to maybe a few dozen waiting threads. If you're writing the next eBay, though, even this will choke when you get hundreds of thousands, or millions, of auctions, and several hundred or thousand begin and end every minute.
If you want it to be 100% reliable, a Windows service that perform all scheduled logic is the way to go. As you say, you cannot trust a web application since it may not even be running.
I'm using c# to communicate with twitter and i need to code a schedule system to send twitter messages at a user defined date.
The messages to be sent are in a database with the date and time of deliver.
Which is the best method to check the db for scheduled messages and send it when the time arrives?
How accurate do you need the timing to be? Could you get away with polling the database every 5 minutes, saying "Tell me all the messages which need to be delivered before current time + 5 minutes" and then sending them all? (And marking them as sent in the database, of course.) Does it matter if they're a bit early or late?
You can do the scheduling on the C# side to make it more accurate, but unless you really need to I'd stick with a very simple solution.
(Depending on your database there may be clever ways of getting callbacks triggered etc... but again, I'd stick with the simplest solution which works.)
In addition to the windows service option (or background thread), you could just set up a scheduled task to run an app that polls the DB and sends the tweets once every defined interval.
Windows schedules can be setup using C# if needed and are really easy to set up manually.
There are several ways to do this, but I guess the best way is to set up a Windows Service that will periodically poll (frequency is up to you) the DB for any scheduled tweets that hasn't been sent.
Needless to say you'll need to handle scenarios such as the Internet connection or DB being down, etc.
In fact the solution consists in using a windows service but it can't communicate directly with the ASP.NET MVC app. I've added a Web Service that handles the task and a System.Threading.Timer in Windows Service to periodically call the Web Service.
Scenario: A WCF service receives an XDocument from clients, processes it and inserts a row in an MS SQL Table.
Multiple clients could be calling the WCF service simultaneously. The call usually doesn't take long (a few secs).
Now I need something to poll the SQL Table and run another set of processes in an asynchronous way.
The 2nd process doesn't have to callback anything nor is related to the WCF in any way. It just needs to read the table and perform a series of methods and maybe a Web Service call (if there are records of course), but that's all.
The WCF service clients consuming the above mentioned service have no idea of this and don't care about it.
I've read about this question in StackOverflow and I also know that a Windows Service would be ideal, but this WCF Service will be hosted on a Shared Hosting (discountasp or similar) and therefore, installing a Windows Service will not be an option (as far as I know).
Given that the architecture is fixed (I.E.: I cannot change the table, it comes from a legacy format, nor change the mechanism of the WCF Service), what would be your suggestion to poll/process this table?
I'd say I need it to check every 10 minutes or so. It doesn't need to be instant.
Thanks.
Cheat. Expose this process as another WCF service and fire a go command from a box under your control at a scheduled time.
Whilst you can fire up background threads in WCF, or use cache expiry as a poor man's scheduler those will stop when your app pool recycles until the next hit on your web site and the app pool spins up again. At least firing the request from a machine you control means you know the app pool will come back up every 10 minutes or so because you've sent a request in its direction.
A web application is not suited at all to be running something at a fixed interval. If there are no requests coming in, there is no code running in the application, and if the application is inactive for a while the IIS can decide to shut it down completely until the next request comes in.
For some applications it isn't at all important that something is run at a specific interval, only that it has been run recently. If that is the case for your application then you could just keep track of when the table was last polled, and for every request check if enough time has passed for the table to be polled again.
If you have access to administer the database, there is a scheduler in SQL Server. It can run queries, stored procedures, and even start processes if you have permission (which is very unlikely on a shared hosting, though).
If you need the code on a specific interval, and you can't access the server to schedule it or run it as a service, or can't use the SQL Server scheduler, it's simply not doable.
Make you application pool "always active" and do whatever you want with your threads.