So I've got a delayed_job task that pushes some info to an XMPP server. Ideally you create a connection to XMPP once and then constantly push data to it, rather than creating a new connection every time you have some data to send.
Is there any kind of facility in delayed_job for running a sort of 'setup' method when a worker starts, have it set some instance variables (like the XMPP connection object) that can then be used by all the jobs that come up? It's okay if each worker runs its own setup method. I just don't want every job (thousands per day) connecting to the XMPP server from scratch every time.
Thanks for any help!
Delayed Job now has "Hooks" (enqueue, before, after, success, error, failure) - it looks like these were added around June 2010. The before hook would probably work in a case where you wanted to find an existing connection to reuse.
Related
I have a kind of proxy server running on a WebServer module and I noticed that this server is being killed due to its memory consumption.
Every time the server gets a new request it creates a child client process, the problem I see is that the process remains alive indefinitely.
Here is the server I'm using:
server.js
I thought response.close() was closing and killing client connections, but it is not.
Here is the list of child processes displayed on htop:
(Those process are even more, it is just a fragment of the list)
I really need to kill those processes because they are using all the free memory. Am I missing something?
I could simply restart the server, but the memory will still be wasted.
Thanks you !
EDIT:
The processes I mentioned before are threads and no independient processes as I thought (check this).
Every http request creates a new thread, and that's ok, but this thread is not being killed after the script ends.
Also, I found out that no new threads are created if the request handler doesn't run casper (I mean casper.run(..)).
So, new threads are created only if the server runs a casper instance, the problem is that this instance doesn't end after run function does.
I tried casper.done() as mentioned below, but it kill the whole process instead of the current running thread. (I did not find any doc for this function).
When I execute other casper scripts, outside the server in the same machine, the instanced threads and the whole phantom process ends successfully. What would be happening?
I am using Phantom 2.1.1 and Casper 1.1.1 versions.
Please ask me anything if you want more or specific information.
Thanks again for reading !
This is a well known issue with casper:
https://github.com/casperjs/casperjs/issues/1355
It has not been fixed by the casper guys and is currently marked as an enhancement. I guess it's not on their priority list.
Anyways, the workaround is to write a server side component e.g. a node.js server to handle the incoming requests and for every request run a casper script to do the scraping in a new child process. This child process will be closed when casper terminates it's job. While this is a workaround, it is not an optimal solution as the cost of opening a child process for every request is not cheap. it will be hard to heavily scale an approach similar to this. However, it is a sufficient workaround. More on this fully sensible approach is in the link above.
I have implemented a Notify/Listen mechanism, so when a special request is sent to the web server, using notify I can notify the workers (in Python) that there's a pending request waiting to be processed.
The implementation works fine, but the problem is that if the workers server is restarting, the notification gets lost, since at that particular time there's no listener.
I can implement a service like MQRabbit or similar, but my needs are so simple that implement such a monster is too much.
Is there any way, a configuration variable perhaps, that can give some persistence to the notification mechanism?
Thanks in advance
I don't think there is a way to persist notification channels, but you can simply store the pending requests to a table, and have the worker check for any missed work on startup.
Either a timestamp or a pending/completed flag would work, depending on what kind of work it's doing.
For consistency, you can have the NOTIFY fire from an INSERT trigger on the queue table, and have the worker always check for any remaining work (not just a specific request) when notified.
I have a WCF Windows Workflow (4.5) Workflow Service hosted under IIS and using AppFabric 1.1. The workflow instances are long-running (up to about a week), but much of the time is spent in Delay activities.
This seemed to work fine at first, but when running multiple instances of the workflow at the same time (2+ instances causes this), some of them just never wake up once they've unloaded from memory during the Delay step. When I look at the logs, the errors I find all look like this:
System.OperationCanceledException: The execution of InstancePersistenceCommands has been canceled because the InstanceHandle was freed.
at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result)
at System.ServiceModel.Activities.Dispatcher.DurableInstanceManager.WaitAndHandleStoreEventsCallback(IAsyncResult result)
Unfortunately, I'm not finding any useful information on that error message.
The SuspensionExceptionName and SuspensionReason fields in the AppFabric Persisted Instances Table show System.NullReferenceException: Object reference not set to an instance of an object. But this doesn't happen inside my workflow, only outside.
Additional Info:
I'm running the activity as a Fire & Forget (receive activity, no send)
My workflow calls into other WCF services to fetch data.
I am running this on Server 2012 R2, IIS 8 (not azure)
Workflow Persistence is working. I can reset IIS, reboot... its just when I run 2 instances that it has problems.
I'm definitely not hitting any kind of throttling limits. While the workflow deals with a few MB of data, this issue happens at 2+ instances.
Any idea what might be happening here?
Edit:
I realized I found more information on how the issue operates and never added it to the question. When the delay issue happens, it operates a lot like a static variable getting written by 2 threads.
Here's a visualization:
WF1 Start ---->Do Stuff--->Sleep------------*1----->Cancelled Exception at some point
------WF 2 Start---->Do Stuff------->Sleep->Wake up---------*2------>More Stuff---->End Successfully
*1 - When WF Instance 1 Should Wake up (Same time as WF 2 wakes)
*2 - When WF Instance 2 Should have woken up (Seems to be ignored)
Before anyone asks... I got rid of every static variable, method, class in my code. Nothing is static anymore.
I've been struggling with similar issues for quite a while. I use WFW4 and I find similar errors when a workflow instance is in a long delay.
I don't know what the cause of the problem is, but I have a work around that you might find helpful.
In my case, the errors I get are from Workflow Management Service and say:
Failed to invoke service management endpoint at 'net.pipe://.svc' to activate service '/Alerts/Workflows/.xamlx'. Exception: 'Access is denied.'
These errors start happening sometime between 6 and 30 hours after the instance goes into a long delay.
I have found that if I create a new instance of the workflow when the first instance is in delay and the errors are happening, then Workflow Management Service is able to resume interacting with the first sleeping instance.
So, I made a new workflow whose sole purpose is to periodically launch and then kill instances of the workflow that contains the long delay.
It actually gets a bit more complicated to make this work. I wanted this new workflow to also go to sleep between times when it creates and kills a new instance of the first workflow. But this going to sleep causes the instance of the new workflow to suffer the same problem as the first workflow. So, I modified the new workflow so it does the following:
-- delay for some rather short period, such as 30 minutes
-- create an instance of the first workflow
-- wait a minute
-- kill the just-created instance of the first workflow
-- create a new instance of this new error-preventing workflow
-- terminate
Since having done this, I no longer get the Access is Denied error from Workflow Management Service!
Hope this helps
Turns out my first answer was not correct, but I believe this answer is right, and solves the issue ChrisG is having.
My workaround did not actually work. Took a while for the problem to resurface. 29 hours to be precise - the default time it takes for an app pool to recycle.
So for me, the solution was to make my app pool not recycle. When an app pool recycles while a workflow instance is in a delay activity, the workflowManagementService is not able to wake up the instance and throws Access is Denied errors. If you create a new instance of the workflow after the app pool has recycled, the first instance will pick up where it left off, but sometimes still has problems, which is what I believe is happening to ChrisG.
ChrisG, looking at your visualization, is it possible that an appPool is recycling during the time wf1 is sleeping? I believe that is the cause the exception. If you then launch a new wf instance after *2 has passed (and if an app pool recycle happened prior to *1), that will wake up both wf1 and wf2, but wf1 won't work properly (at least in my experience)
Also, this happens after iisresets and server reboots. To handle those, you need to use IIS7 which allows the web application (as well as the web site) which is hosting the xamlx files to autostart after an iisreset or server reboot. This option is not available in IIS6. See http://www.postseek.com/meta/991815402b369e71ce925cde47ac907d for details
Hope this helps!
I have recently been thinking about possible architecture for a simple task reminder system. User will schedule a task and reminder in form of SMS/email/android needs to be sent to all stakeholders at some x minutes before the task is scheduled to be performed(much in the same way google calendar works). The problem here is to send the reminder at that precise point in time. Here are the two possible approaches I can think of:
Cron: I can setup a cron to run every minute. This will scan the table for notifications which need to be sent in the next minute and simply sends the notifications. But, precision is lost as there is always the chance of that +/-1 min error.
Work Queues: I can simply put a message with appropriate delay in a queue at the time task was scheduled. Workers will send the notification as and when they receive the message. I can add as many workers as I want in case my real time behavior starts getting affected because of load. There are still a few issues. How to choose the appropriate work queue? I have evaluated RabbitMq and Beanstalk. While Rabbitmq follows standard AMQP protocol and is widely suggested, it doesn't provide the delay functionality out of the box. There are ways to simulate this using dead-letter-exchanges but this will not work in my case because the delay needs to be variable. Beanstalk supports this but the problem is that beanstalk queue resides entirely in memory which I don't like(but can live with). Any possible alternatives?
Third Approach: ??????. I am sure a simple desktop notification tool does neither of the two. What technology do they use to achieve the same thing?
We had the same scenario and we use Redis for long schedules even now reminders for up to 2 years. You can use Sorted Set where the timestamp is the score.
We use Beanstalkd delay jobs for those kind of reminders where we know it's relatively short term couple of hours, and there is no cancellations, as removing from beanstalkd a delayed message you need to retain the job id in a database for later removal, and that is no viable.
Although you mention memory limit, we use persistence on both Redis/Beanstalkd
I have a building block which sets up a Quartz job to send out emails every morning. The job is fired three times every morning instead of once. We have a hosted instance of Blackboard, which I am told runs on three virtual servers. I am guessing this is what is causing the problem, as the building block was previously working fine on a single server installation.
Does anyone have Quartz experience, or could suggest how one might prevent the job from firing multiple times?
Thanks,
You didn't describe in detail how your Quartz instance(s) are being instantiated and started, but be aware that undefined behavior will result if you run multiple Quartz instances against the same job store database at the same time, unless you enable clustering (see http://www.quartz-scheduler.org/docs/configuration/ConfigJDBCJobStoreClustering.html).
I guess I'm a little late responding to this, but we have a similar sort of scenario with our application. We have 4 servers running jobs, some of which can run on multiple servers concurrently, and some should only be run once. As Will's response said, you can look into the clustering features of Quartz.
Our approach was a bit different, as we had a home-grown solution in place before we switched to Quartz. Our jobs utilize a database table that store the cron triggers and other job information, and then "lock" the entry for a job so that none of the other servers can execute it. This keeps jobs from running multiple-times on the servers, and has been fairly effective so far.
Hope that helps.
I had the same issue before but I discovered that I was calling scheduler.scheduleJob(job, trigger); to update the job data while the job is running which is randomly triggered the job 5-6 times each run. I had to use the following to update the job data without updating the trigger scheduler.addJob(job, true);