sorl-thumbnail - Slow template rendering - django

Question

I have serious performing problem with my templates. After some test, I found out that the slowest part from the rendering was the thumbnails, generated from sorl-thumbnail.
Below is the issued part from my template:
{% for listing in listings %}
<li class="pic_view">
<ul>
<li class="picture">
<a href="{% url 'listing' listing.id listing.title %}">
{% thumbnail listing.get_picture "240x143" crop="center" as im %}
<img src="{{ im.url }}">
{% empty %}
tc
{% endthumbnail %}
<div class="overlay"></div>
</a>
</li>
<li class="artist">
<a href="{% url 'profile_artist' listing.artist_id listing.artist.user.first_name %}">
{% thumbnail listing.artist.get_avatar "60x60" crop="center" as im %}
<img src="{{ im.url }}">
{% empty %}
tc
{% endthumbnail %}
</a>
</li>
</ul>
</li>
{% endfor %}
Currently I have about 6 listings and below is the measured time for rendering:
- 8512 ms on first rendering
- 4680 ms on reload
- 112 ms when thumbnail tags are removed
Can you please give me some advice on this point. The number above are measured with Debug=True, but there is no difference when the flag is False. Also accordingly to Django documentation, I have included the followings TEMPLATE_LOADERS:
TEMPLATE_LOADERS = (
'django.template.loaders.filesystem.Loader',
'django.template.loaders.app_directories.Loader',
('django.template.loaders.cached.Loader', (
'django.template.loaders.filesystem.Loader',
'django.template.loaders.app_directories.Loader',
)),
)

Answer 1

Sorl does this behind the scenes (the chapter in the docs are here, here is the TL;DR version)
Compute a hash value from the original file name and the options
given
Check in the database if that hash is already present, if so,
deliver associated thumbnail
If not, resize the image, store it in the media location, create a
database record with the hash/filename association, deliver
thumbnail
That being said, 4.5 seconds for a couple of database lookups is wayyyyyy too long. There is something else going on here.

Answer 2

Sorl Thumbnail generates thumbnails on the fly hence time consuming operation, what you need is to create the thumbnails using cronjob or celery (preferred) with the preferred sizes. There is package already called sorl-thumbnail-async which does what you are looking for and uses celery. So if the thumbnails are not available show dummy image as soon as the thumbnails are available they will be rendered. Also use memcached as a cache backend for django which is really good in terms of performance.