4

So I have a lot of internal and external APIs that are called on basically each request. This means that there's a lot of setting up connections to these APIs. Is there a way of creating a persistent connection object that can be shared between requests?

So I'd like to replace:

def a(request):
    c = api.connect()
    c.call_function()

With:

def b(request):
    // use existing connection object from earlier request
    c.call_function()

Any ideas?

I'm also not sure how big the gain would be but I don't mind doing some benchmarking once I have a first solution.

olofom
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2 Answers2

5

Quite simple really 

conn = api.connect() # This line is run only once when the process starts and the module is loaded 

def view(request):
    conn.call_function() # This line is run every time a request is received

This connection would be shared by any request using the same worker/server process. So if you have three workers serving your application you would have at most three connections.

I would worry that the connections might start timing out. So you would want to guard against that. Perhaps by having a function that checked the state of the connection, returned it if it was still good, or creating a new one if it had expired.

Why this works can be illustrated with the following example:

>>> a = 1
>>> def add(b):
...     print a + b
... 
>>> add(2)
3

Note that you can't modify the connection without using the global keyword

>>> def change(c):
...     a = c
...     print a
... 
>>> change(4)
4
>>> print a
1

Compare:

>>> a = 1
>>> def change(d):
...     global a
...     a = d
...     print a
... 
>>> change(5)
5
>>> print a
5
>>>

If you want to share the api connection between different workers/processes it becomes a bit trickier. i.e don't bother.

aychedee
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  • Ehm... it turned out that as long as i don't try to set it it works fine. So accessing conn works but if I try to set conn further down (after reading it) it crashes on the read... I'll updated my question with example. – olofom Aug 02 '13 at 13:13
  • Why are you trying to assign to conn? I thought the whole point was persisting a connection? If you want to change the global, you have to use the global keyword. – aychedee Aug 02 '13 at 13:23
0

In addition to aychedee's answer I would suggest you to take a look at django's database persistent connections, which are new for Django 1.6. The idea:

Persistent connections avoid the overhead of re-establishing a connection to the database in each request.

You can implement something similar for your own needs.

Code on Github in Django's 1.6 branch. It's complicated enough but contains connection expiring and usability check logic.

Alex Emelin
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