Django Cache + Django Database request

Question

I'm building a Django web application which allow users to select a photo from the computer system and keep populating onto the users timeline. The timeline will be showing 10 photos initially and then have a pull to refresh to fetch the next 10 photos on the timeline.

So my first question is I'm able to upload images which gets store on the file system,but how do I show only first 10 and then pull a refresh to fetch the next 10 and so on.

Next, I want the user experience of the app to be fast. So, I'm considering caching. So, i was thinking, what do I cache. Since there are 3 types of cache in Django- Database cache, MemCache, or FileSystem Caching. So my secon question is should I cache the first 10 photos of each user or something else?

Kindly answer with your suggestions.

Bibhas Debnath · Accepted Answer · 2013-07-31T05:50:47.280

So my first question is I'm able to upload images which gets store on the file system,but how do I show only first 10 and then pull a refresh to fetch the next 10 and so on.

Fetch first 10 with your initial logic, fetch next photos in chronological order. You must have some timestamp relating to your photo posting. Fetch images according to that. You can use Django Paginator for this.

what do I cache

Whatever static data you want to show to the user frequently and wont change right away. You can cache per user or for all users. According to that you choose what to cache.

should I cache the first 10 photos of each user or something else

Depends on you. Are those first pictures common to all the users? Then you can cache. If not and the pictures are user dependent, there is no point caching them. The user will anyway have to fetch the first images. And I highly doubt the user will keep asking for the same first 10 photos frequently. Again, it's your logic. If you think caching will help, you can go ahead and cache.

Nice and Informative guide about the caching part, but I have a query for fetching the next 10 images. I have this statement in my views.py file `documents = Document.objects.filter(owner=request.user)[page_no:page_no+5]`. The page_no initially starts from `0`. I have a `next` button in my templates, which will fetch my next 10 pics. So, I was thinking of using jQuery+AJAX. So, how will I send the data via jQuery stating which set of pics should be displayed, ie either 11-20 or 21-30 or 31-40 and so on. — Praful Bagai, Jul 30 '13 at 19:32

score 1 · Answer 2 · answered Mar 19 '16 at 05:33

The DiskCache project was first created for a similar problem (caching images). It includes a couple of features that will help you to cache and serve images efficiently. DiskCache is an Apache2 licensed disk and file backed cache library, written in pure-Python, and compatible with Django.

diskcache.DjangoCache provides a Django-compatible cache interface with a few extra features. In particular, the get and set methods permit reading and writing files. An example:

from django.core.cache import cache

with open('filename.jpg', 'rb') as reader:
    cache.set('filename.jpg', reader, read=True)

Later you can get a reference to the file:

reader = cache.get('filename.jpg', read=True)

If you simply wanted the name of the file on disk (in the cache):

try:
    with cache.get('filename.jpg', read=True) as reader:
        filename = reader.name
except AttributeError:
    filename = None

The code above requests a file from the cache. If there is no such value, it will return None. None will cause an exception to be raised by the with statement because it lacks an __exit__ method. In that case, the exception is caught and filename is set to None.

With the filename, you can use something like X-Accel-Redirect to tell Nginx to serve the file directly from disk.

Django Cache + Django Database request

2 Answers2