Re: 2D map application: performance and design question

Hi Lars,

Unless you are doing some *really* intense Python code in your business logic, then 9 out of 10 times, the bottleneck is usually the database, especially if you are using Python.

Cal

On Mon, Nov 1, 2010 at 9:59 AM, Lars Ruoff <lars.ruoff@gmail.com> wrote:

Hello,

first of all, these are my first steps with Django, and i only have
limited experience with Python, so please be patient.

I'm using it for what is intended to be a browser game in the future.
The main part of the game is a zoom view on a two-dimensional map of
fields.

I'm currently using Django 1.2.3 with Python 2.6 on Windows XP.
I'm using Python-provided SQLite and Django's local debug HTTP server
during development ('python manage.py runserver').

It works pretty well, but i notice that it takes several seconds to
update the map screen, which i consider unacceptable given the fact
that it runs locally.

I'm wondering where the performance bottleneck lies here.
Is it...
- SQLLite? (I.e. would switching to say PostgreSQL speed things up
considerably?)
- Djangos debug web server? (I.e. would switching to apache speed
things up considerably?)
- or the way my application is designed??

Since the latter is a very probable answer, here is the way it works
in a nutshell:

The model is something like:
--------------------
class Terrain(models.Model):
   image_file = models.CharField(max_length=80)

class Location(models.Model):
   x = models.IntegerField()
   y = models.IntegerField()
   terrain = models.ForeignKey(Terrain)


The heart of the view goes like this:
--------------------
   center_location = Location.objects.get(id=location_id)

   ## how many fields on the map view in each direction
   half_x = 6
   half_y = 6

   locations = Location.objects.filter( \
       x__gte=center_location.x-half_x, \
       x__lte=center_location.x+half_x, \
       y__gte=center_location.y-half_y, \
       y__lte=center_location.y+half_y)

   locs = []
   for l in locations:
       loc_info = {'id': l.id, \
           'x': l.x - center_location.x + half_x, \
           'y': l.y - center_location.y + half_y, \
           'img': l.terrain.image_file}
       locs.append(loc_info)

   c = Context({
       'locs': locs,
   })
   return HttpResponse(t.render(c))


And the main part of the template renders these items:
--------------------
{% for l in locs %}
<div id="x{{l.x}}y{{l.y}}" class="tile"><a href="/map/{{l.id}}/"><img
src="/images/{{l.img}}" /></a></div>
{% endfor %}


Do you see any issues with this approach? Any paths to performance
improvements?
Since i'm at the beginning of this project i would like to avoid going
the wrong way.

best regards,
Lars

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