What is the preferred way to write my linux daemons?

Question

Hello to All

I have a PHP website that should use some cached data (stored in Memcache, for example). The data should be stored in cache by daemons fetching it from web services and some of it should be stored in MySQL server too.

The daemons should do the following:

1. Fetch foreign exchange rates, parse them and store them in database as well as in two seperated memcaches in seperate machines.
2. Fetch financial indices and store it in seperated memcaches.
3. Fetch large XML data and store it in two seperated memcaches.

I am capable of writing these daemons in C/C++/Perl/PHP/Python.

I have to decide in which language/script I should choose in order to implement these daemons. The advantage of using PHP for this is that I can use API used by the website application itself. Another advantage is that PHP is easy and everyone knows it so I won't be tied up to maintaining these daemons but on the other hand PHP is slower and consumes much more resources.

The main disadvantage of using other language than PHP is that it's harder to maintain code written in C/C++/Perl. Nowadays, I guess it's not common to do these kind of tasks using C/C++/Perl. Am I wrong in saying that ?

What would you recommend me to do in this case ?

Answer 1

Perl and Python are default answers for writing such scripts. But it doesn't matter (much) what language you use if you write good code. The more importat thing is that how you handle your script on failure.

In the long run you may see your scripts are failing seldom for arbitrary reasons, and it may not worth for you to debug the script because it usually does a fair job and it would be difficult to find where it went wrong.

I have few perl scripts doing the same kind of thing that you are doing. to me the tricky part was to make sure that my scripts don't fail for long because I didn't want to miss a chunck of live streamed data.

And for that I used monit . A great tool.

Answer 2

The best choice would probably be PHP for simplicity/code reuse.

PEAR System Daemon
Create daemons in php

EDIT
From what I can tell it's just passing data around, it's no performance to worry about. And about resource usage just make sure not to run out of max_memory (by means of streaming maybe or configure plenty). Abort and log operations that take too long. Reconnect to the database in a loop when SQL operation fail etc.

NOTE OF CAUTION
Daemon programming is tricky and a lot of things can go wrong. Take into considerations all points of failure.

Also, note that Perl is a lot more versed in regards to daemons than PHP. I left out c/c++ as performance (pass data around) is not an issue and daemon programming is hard enough as it it, why add worries on memory leaks, segfaults etc. ?