Sunday, January 31, 2016

Re: Kind'a TL, but please DR - Need your thoughts

if a process takes too long to complete it won't be able to process new requests, so you will be limited to the number of workers you told uwsgi to use.

http requests should be short lived, if you have some heavy processing  to do the http request should return with something like 'accepted' and send the job to a queue (you can use celery)

On Mon, Feb 1, 2016 at 6:51 AM, Mario R. Osorio <nimbiotics@gmail.com> wrote:

I need comments on an application I have been recently proposed. The way it is being envisioned at this moment is this:


One python daemon will be listening for different communications media such as email, web and SMS (web also). IMHO, it is necessary to have a daemon per each media. This daemon(s) will only make sure the messages are received from a validated source and put such messages in a DB


A second(?) python daemon would be waiting for those messages to be in the DB, process them, act accordingly to the objective of the application, and update the DB as expected. This process(es) might included complicated and numerous mathematical calculations, which might take seconds and even minutes to process.


A third(?) python daemon would be in charge of replying to the original message with the obtained results, but there might be other media channels involved, eg the message was received from a given email or SMS user, but the results have to be sent to multiple other email/SMS users.


The reason I want to do the application using Django is that all this HAS to have multiple web interfaces and, at the end of the day most media will come through web, and have to be processed as http requests. Also, Django gives me a frame to make this work better organized and clean and I can make the application(s) DB agnostic.


Wanting the application to be DB agnostic does not mean that I don't have a choice: I know I have many options to communicate among different python processes, but I prefer to leave that to the DBMS. Of the open source DBMS I know of, only Firebird and PostgreSQL have event that can provide the communication between all the processes involved. I was able to create a very similar application in 2012 with Firebird, but this time I am being restricted to PostgreSQL, which I don't to oppose at all. That application did not involve http requests.


My biggest concern at this point is this:

If most (if not all) requests to the application are going to be processed as http requests, what will happen to pending requests when one of them takes too long to reply? Is this something to be solved at the application level or at the server level?



This is as simple as I can put it. Any thoughts, comments, criticism or recommendations are welcome.


Thanks a lot in advanced!

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