I have a Gearman Work in php that processes background tasks from client. From time to time I am not able to process that job. I would need a way to delay retry that job after 5 minutes. How can I do that?
What I do now is to do exit(255) but this will retry the job immediately. Also I do not know how can I get the number of failures of that specific job (in the worker).
Questions:
How can I do the above stuff in Gearmand
Is there any other
messageing system that is capable of this?
You can't. At least not using built-in capabilities. This feature is only partly implemented in Gearmand and the PHP module does not expose this functionality. See this discussion on the feature.
People have tried different things, including:
Use node.js and its timeout capabilities
Use at utility
Use another queuing system - beanstalkd
When it comes to tracking failures - again, you can't, AFAIK. See my answer on handling retries in Gearman for a possible solution.
Not build in, but you can use a bit of memcached+TTL for that.
Related
Would appreciate some help understanding typical best practices in carrying out a series of tasks using Gearman in conjunction with PHP (among other things).
Here is the basic scenario:
A user uploads a set of image files through a web-based interface. The php code responding to the POST request generates an entry in a database for each file, mostly with null entries in the columns, queues a job for each to do analysis using Gearman, generates a status page and exits.
The Gearman worker gets a job for a file and starts a relatively long-running analysis. The result of that analysis is a set of parameters that need to be inserted back into the database record for that file.
My question is, what is the generally accepted method of doing this? Should I use a callback that will ultimately kick off a different php script that is going to do the modification, or should the worker function itself do the database modification?
Everything is currently running on the same machine; I'm planning on using Gearman for background scheduling, rather than for scaling by farming out to different machines, but in any case any of the functions could connect to the database wherever it is.
Any thoughts appreciated; just looking for some insights on how this typically gets structured and what might be considered best practice.
Are you sure you want to use Gearman? I only ask because it was the defacto PHP job server about 15 years ago but hasn't been a reliable solution for quite some time. I am not sure if things have drastically improved in the last 12 months, but last time I evaluated Gearman, it wasn't production capable.
Now, on to the questions.
what is the generally accepted method of doing this? Should I use a callback that will ultimately kick off a different php script that is going to do the modification, or should the worker function itself do the database modification?
You are going to follow this general pattern with any job queue:
Collect a unit of work. In your case, it will be 1 of the images and any information about who that image belongs to, user id, etc.
Submit the work to the job queue with this information.
Job Queue's worker process picks up the work, and starts processing it. This is where I would create records in the database as you can opt to not create them on job failure.
The job queue is going to track which jobs have completed and usually the status of completion. If you are using gearman, this is the gearmand process. You also need something pickup work and process that work, I will refer to this as the job worker. The job worker is where the concurrency happens which is what i think you were referring to when you said "kick off a different php script." You can just kick off a PHP script at an interval (with supervisord or a cronjob) for a kind of poll & fork approach. It's not the most efficient approach, but it doesn't sound like it will really matter for your applications use case. You could also use pcntl_fork or pthreads in PHP to get more control over your concurrent processes and implement a worker pool pattern, but it is much more complicated than just firing off a script. If you are interested in trying to implement some concurrency in PHP, I have a proof-of-concept job worker for beanstalkd available on GitHub that implements a worker pool with both fork and pthreads. I have also include a couple of other resources on the subject of concurrency.
Job Worker (pthreads)
Job Worker (fork)
PHP Daemon Example
PHP IPC Example
I have implemented a command in my Symfony setup which grabs a job from the DB and then processes it.
How can I run multiple instances of command at once, to get through jobs quicker. I know that multithreading is not supported in PHP but seeing as the command is called from the shell, I was wondering if there was a workaround.
Call command using:
app/console job:process
The way I would solve this is to use a work queue with multiple workers. It's easier to manage and scale than manually running multiple processes and worrying about concurrency.
The simplest general-purpose queue I've found for working with php/symfony is beanstalkd which you can integrate into symfony2 with the LeezyPheanstalkBundle
In general, I'd suggest using enqueue library. You can choose from a variety of transports available, from the simplest like filesystem and Doctrine DBAL to real once like RabbitMQ and Amazon SQS.
Regarding the consumers, you need sort of process manager. There several options:
http://supervisord.org/ - You need extra service. It has to be configured properly.
A pure PHP process manager like this. Based on Symfony process component and pure PHP code. It can handle process reboot, correct exit on sigterm signal and a lot more.
A php\swoole process manager like this. It requires a swoole PHP extension but it is performance is amazing.
I have written a blog post on how to solve this exact problem. https://plume.baucum.me/~/Absolutely/running-multiple-processes-simultaneously-in-a-symfony-command
It is much too long to rehash everything here, but the basic concept is that your command optionally takes in the job's ID. The command will check if the ID was given. If not then it will grab all the jobs from the DB, loop over them, and recall itself with the job ID parameter. As each command is kicked off you store it in an array, and if the array is too big you sleep, for rate throttling. As commands finish you remove them from the array.
When the command is ran with the job ID it will create a lock using Symfony's lock component so that a job cannot accidentally be processed two times at once. It is important that you unlock the job when it either finishes or errors out. Once it has the ID and the lock it will then call whatever code you have written to actually process the job.
Using this technique I have taken commands that took hours to run, as it synchronously went through each task, into taking only minutes. Make sure to try different throttles to balance resource utilization and time it takes to execute your task.
I have a web-app, written in PHP, and I am using Symfony2 as the core framework.
I need to regularly run thousands of small network requests every 10 minutes or so and I am trying to find the best solution for asynchronously running these jobs, without conflicting or doubling up.
Currently I have a very basic and inelegant solution where a cron job executes a PHP command script. The command synchronously works through each entry in the database and sends a network request. When that request completes (or fails), it moves on to the next one. When it has iterated over all entries, it exists, to be executed again from the cron job.
For the rewrite, I have looked at php-resque and pcntl_fork as solutions for running jobs in parallel, thereby speeding up the execution significantly. I have also looked at running multiple non-blocking socket requests from PHP but, so far, have preferred the simplicity of isolated jobs.
PHP can't do threading in the traditional sense, so what you're trying to do isn't really possible in the way that you're thinking. You've looked at the best solution (probably) in pcntl_fork, but that still won't be truly asynchronous. Have you considered using cron to accomplish this instead?
http://php.net/pthreads
http://github.com/krakjoe/pthreads
Examples on github... and included in distribution, use code in github, it contains fixes not yet released.
I am handling a project which contain message queue concept. Now the project is in PHP, and it's making more delay in message sending or mail sending. So I suggest to develop a message queue in Perl or Python script. Could you please suggest which is best either PHP or Perl or Python?
A possible solution could be to use Gearman as a queue :
Your PHP project would send messages to Gearman, as background jobs ; and finish
Gearman would dispatch those messages to workers
Workers will deal with the jobs -- doing the stuff that might take time
One additional advantage : the day you need several servers to handle a larger amount of jobs, you'll already have what's needed : Gearman will deal with load-balancing for you.
PHP is perfectly adequate to implement a simple message queue. So, if your current code is causing delays then it is because of your design, not because of some limitation with PHP. Switching to a different language isn't going to help you. Bad code is bad code regardless of language.
The best thing you can probably do is going with an existing message queue. Pascal recommended Gearman. I have worked with (and quite liked) Beanstalkd. If you need a metric ton of features, have a look at ApacheMQ or RabbitMQ.
That said, if you insist on implementing your own message queue, I would suggest sticking with PHP. That way you can re-use code from your existing application (e.g. re-use your models and database API for example).
Here are two alternative for gearman
a. Beanstalkd
b. MemcacheQ
MemcacheQ http://memcachedb.org/memcacheq/
Adding and fetching from queue needs to be done manually using code.
Its not like you send it to queue and MemcacheQ will execute it one by one.
but its very very fast.
Beanstalkd
http://kr.github.com/beanstalkd/download.html
It supports many languages.
I am creating a web application using zend, here I create an interface from where user-A can send email to more than one user(s) & it works excellent but it slow the execution time because of which user-A wait too much for the "acknowledged response" ( which will show after the emails have sent. )
In Java there are "Threads" by which we can perform that task (send emails) & it does not slow the rest application.
Is there any technique in PHP/Zend just like in Java by which we can divide our tasks which could take much time eg: sending emails.
EDIT (thanks #Efazati, there seems to be new development in this direction)
http://php.net/manual/en/book.pthreads.php
Caution: (from here on the bottom):
pthreads was, and is, an experiment with pretty good results. Any of its limitations or features may change at any time; [...]
/EDIT
No threads in PHP!
The workaround is to store jobs in a queue (say rows in a table with the emails) and have a cronjob call your php script at a given interval (say 2 minutes) and poll for jobs. When jobs present fetch a few (depending on your php's install timeout) and send emails.
The main idea to defer execution:
main script adds jobs in the queue
cron script sends them in tiny slices
Gotchas:
make sure u don't send an email without deleting from queue (worst case would be if a user rescieves some spam at 2 mins interval ...)
make sure you don't delete a job without executing it first ...
handle bouncing email using a score algorithm
You could look into using multiple processes, such as with fork. The communication between them wouldn't be as simple as with threads (but then, it won't come with all of its pitfalls either), but if you're just sending emails, it might not be necessary to communicate much, if at all.
Watch out for doing forks on an Apache process. You may get some behaviors that you are not expecting. If you are looking to do any kind of asynchronous execution it should be via some kind of queuing mechanism. Gearman is one. Zend Server Job Queue is another. I have some demo code at Do you queue? Introduction to the Zend Server Job Queue. Cron can be used, but you'll have the problem of depending on your cron scheduler to run tasks whereas asynchronous computing often needs to be run immediately. Using a queuing system allows you to do that without threading.
There is a Threading extension being developed based on PThreads that looks promising at https://github.com/krakjoe/pthreads
There is pcntl, which allows you to create sub-processes, but php doesn't work very well for this kind of architecture. You're probably better off creating a long-running script (a daemon) and spawning multiple of them.
As of PHP there are no threads in it. However for php, you can have a look at this roundabout way
http://www.alternateinterior.com/2007/05/multi-threading-strategies-in-php.html
You may want to use a queue system for your email sending and send the email from another system which supports threads. PHP is just a tool and you should the tool that is best fitted for the job.
PHP doesn't include threading as part of the language, there are some methods that can emulate it but they aren't foolproof.
This Google search shows a few potential workarounds