I have a simple rest endpoint that executes Postgres procedure.
This procedure returns the current state of device.
For example:
20 devices.
Client app connect to API and make 20 responses to that endpoint every second.
For x clients there are x*20 requests.
For 2 clients 40 requests.
It causes a big cpu load on Postgres server only if there are many clients and/or many devices.
I didn’t create it but I need to redesign it.
How to limit concurrent queries to db only for it? It would be a hot fix.
My second idea is to create background worker that executes queries only one in the same time. Then the endpoint fetches data from memory.
I would try the simple way first. Try to reduce
the amount of database connections in the pool OR
the amount of working threads in the build-in Tomcat.
More flexible option would be to put the logic behind a thread pool limiting the amount of working threads. It is not trivial, if the Spring context and database is used inside a worker. Take a look on a Spring annotation #Async.
Offtopic: The solution we are discussing here looks like a workaround. The discussed solution alone will most probably increase the throughput only by factor 2 maybe 3. It is not JEE conform and it will be most probably not very stable. It is better to refactor the application avoiding such a problem. Another option would be to buy a new database server.
Update: JEE compliant solution would be to implement some sort of bulkhead pattern. It will limit the amount of concurrent running requests and reject it, if the some critical number is reached. The server application answers with "503 Service Unavailable". The client application catches this status and retries a second later (see "exponential backoff").
I want to increase the 'session timeout', which currently is set to 20 minutes. How can I increase or decrease it by one hour, or in other terms, 60 minutes?
There are a few ways to accomplish what you need, as we ran into the same issue when doing our NetSuite integration.
You can make a dummy search event every couple of min. We searched for a bogus transaction that we knew would never be created, and limited to a date in the distant past and only that date. That way the search would return very quickly with zero results.
Implement SingleSignOn. This is the preferred method. Once you initiate the single sign on, if the session has timed out on you previously you can quickly make a new session using tokens and do not need to ask the user for their username/password again.
We had a service that needed consumed at two different points in the application that did not know about each other. So the way we got around this but still using one service was saving the cookies from the service in a shared location. Then when the service is needed by one of the application they would recreate the service from the cookies. If the service had timed out we would recreate the service and update the cookies. This method became outdated once we implimented SingleSignOn, as then we could just create the service from the tokens as needed, and the tokens were stored in a shared location.
Hope this helped.
There is no standard way that I know of in NetSuite, you could though use a browser plugin to refresh the page or click the home button every 19 mins. Would work if for example the person is AFK.
There is no way to change the web service request timeout period (for sync operations it lasts approx 15 min, then the operation gets terminated on the server side). The general practice for long running operations that takes more than 15 mins is to use async requests.
I'm trying to create a real-time webbrowser game in ASP.Net MVC3, but I'm unsure about what's the best approach to processing 'real-time' events on the server side.
Imagine that the client wants to upgrade a building, upgrading a building takes time. A record gets inserted in the database that holds the end-time and on the client a ajax timer start's running. I was thinking about having a windows service running all the time. Every second the service checks the table and does the real processing when the time passed the end-time. However I could imagine that when you have a huge amount of data to process this can get problematic.
What would be the best way of doing this?
Cheers.
I've seen games like that before. You do not need to count down yourself, you just need to store the datetime for whenever the building will be ready.
When a page is requested you send a timestamp of when the building will be completed, and use javascript to count down. For example, like this.
A web application I am developing needs to perform tasks that are too long to be executed during the http request/response cycle. Typically, the user will perform the request, the server will take this request and, among other things, run some scripts to generate data (for example, render images with povray).
Of course, these tasks can take a long time, so the server should not hang for the scripts to complete execution before sending the response to the client. I therefore need to perform the execution of the scripts async, and give the client a "the resource is here, but not ready" and probably tell it a ajax endpoint to poll, so it can retrieve and display the resource when ready.
Now, my question is not relative to the design (although I would very much enjoy any hints on this regard as well). My question is: does a system to solve this issue already exists, so I do not reinvent the square wheel ? If I had to, I would use a process queue manager to submit the task and put a HTTP endpoint to shoot out the status, something like "pending", "aborted", "completed" to the ajax client, but if something similar already exists specifically for this task, I would mostly enjoy it.
I am working in python+django.
Edit: Please note that the main issue here is not how the server and the client must negotiate and exchange information about the status of the task.
The issue is how the server handles the submission and enqueue of very long tasks. In other words, I need a better system than having my server submit scripts on LSF. Not that it would not work, but I think it's a bit too much...
Edit 2: I added a bounty to see if I can get some other answer. I checked pyprocessing, but I cannot perform submission of a job and reconnect to the queue at a later stage.
You should avoid re-inventing the wheel here.
Check out gearman. It has libraries in a lot of languages (including python) and is fairly popular. Not sure if anyone has any out of the box ways to easily connect up django to gearman and ajax calls, but it shouldn't be do complicated to do that part yourself.
The basic idea is that you run the gearman job server (or multiple job servers), have your web request queue up a job (like 'resize_photo') with some arguments (like '{photo_id: 1234}'). You queue this as a background task. You get a handle back. Your ajax request is then going to poll on that handle value until it's marked as complete.
Then you have a worker (or probably many) that is a separate python process connect up to this job server and registers itself for 'resize_photo' jobs, does the work and then marks it as complete.
I also found this blog post that does a pretty good job summarizing it's usage.
You can try two approachs:
To call webserver every n interval and inform a job id; server processes and return some information about current execution of that task
To implement a long running page, sending data every n interval; for client, that HTTP request will "always" be "loading" and it needs to collect new information every time a new data piece is received.
About second option, you can to learn more by reading about Comet; Using ASP.NET, you can do something similiar by implementing System.Web.IHttpAsyncHandler interface.
I don't know of a system that does it, but it would be fairly easy to implement one's own system:
create a database table with jobid, jobparameters, jobresult
jobresult is a string that will hold a pickle of the result
jobparameters is a pickled list of input arguments
when the server starts working on a job, it creates a new row in the table, and spwans a new process to handle that, passing that process the jobid
the task handler process updates the jobresult in the table when it has finished
a webpage (xmlrpc or whatever you are using) contains a method 'getResult(jobid)' that will check the table for a jobresult
if it finds a result, it returns the result, and deletes the row from the table
otherwise it returns an empty list, or None, or your preferred return value to signal that the job is not finished yet
There are a few edge-cases to take care of so an existing framework would clearly be better as you say.
At first You need some separate "worker" service, which will be started separately at powerup and communicated with http-request handlers via some local IPC like UNIX-socket(fast) or database(simple).
During handling request cgi ask from worker state or other data and replay to client.
You can signal that a resource is being "worked on" by replying with a 202 HTTP code: the Client side will have to retry later to get the completed resource. Depending on the case, you might have to issue a "request id" in order to match a request with a response.
Alternatively, you could have a look at existing COMET libraries which might fill your needs more "out of the box". I am not sure if there are any that match your current Django design though.
Probably not a great answer for the python/django solution you are working with, but we use Microsoft Message Queue for things just like this. It basically runs like this
Website updates a database row somewhere with a "Processing" status
Website sends a message to the MSMQ (this is a non blocking call so it returns control back to the website right away)
Windows service (could be any program really) is "watching" the MSMQ and gets the message
Windows service updates the database row with a "Finished" status.
That's the gist of it anyways. It's been quite reliable for us and really straight forward to scale and manage.
-al
Another good option for python and django is Celery.
And if you think that Celery is too heavy for your needs then you might want to look at simple distributed taskqueue.
I am creating a service which receives some data from mobile phones and saves it to the database.
The phone is sending the data every 250 ms. As I noticed that the delay for data storing is increasing I tried to run WireShark and write a log as well.
I noticed that the web requests from mobile phone are being made without the delay (checked with WireShark), but the in the service log I noticed the request is received every second and a half or almost two seconds.
Does anyone know where could be the problem or the way to test and determine the cause of such delay?
I am creating a service with WCF (webHttpBinding) and the database is MS SQL.
By the way the log stores the time of http request and also the time of writing data to the database. As mentioned above the request is received every 1.5 - 2 seconds and after that it takes 50 ms to store data to the database.
Thanks!
My first guess after reading the question was that maybe you are submitting data so fast, the database server is hitting a write-contention lock (e.g. AutoNumber fields?)
If your database platform is SQL Server, take a look at http://www.sql-server-performance.com/articles/per/lock_contention_nolock_rowlock_p1.aspx
Anyway please post more information about the overall architecture of the system... what softwares/platforms are used at what parts etc...
Maybe there is some limitation in the connection imposed by the service provider?
What happens if you (for testing) don't write to the database and just log the page hits in the server log with timestamp?
Check that you do not have any tracing running on the web services, this can really kill perf.