How can i improve performances when using django queryset? - sql

Question

I'm trying to make a news feed. Each time the page is called, server must send multiple items. One item contain a post, number of likes, number of comments, number of comment children, comments data, comment children data etc.
My problem is, each time my page is called, it takes more than 5 secondes to be loaded. I've already implemented a caching system. But it's still slow.
posts = Posts.objects.filter(page="feed").order_by('-likes')[:'10'].cache()
posts = PostsSerializer(post,many=True)
hasPosted = Posts.objects.filter(page="feed",author="me").cache()
hasPosted = PostsSerializer(hasPosted,many=True)
for post in post.data:
commentsNum = Comments.objects.filter(parent=posts["id"]).cache(ops=['count'])
post["comments"] = len(commentsNum)
comments = Comments.objects.filter(parent=posts["id"]).order_by('-likes')[:'10'].cache()
liked = Likes.objects.filter(post_id=posts["id"],author="me").cache()
comments = CommentsSerializer(comments,many=True)
commentsObj[posts["id"]] = {}
for comment in comments.data:
children = CommentChildren.objects.filter(parent=comment["id"]).order_by('date')[:'10'].cache()
numChildren = CommentChildren.objects.filter(parent=comment["id"]).cache(ops=['count'])
posts["comments"] = posts["comments"] + len(numChildren)
children = CommentChildrenSerializer(children,many=True)
liked = Likes.objects.filter(post_id=comment["id"],author="me").cache()
for child in children.data:
if child["parent"] == comment["id"]:
liked = Liked.objects.filter(post_id=child["id"],author="me").cache()
I'm trying to find a simple method to fetch all these data quicker and without unnecessary database hit. I need to reduce the loading time from 5 secs to less than 1 if possible.
Any suggestion ?

Answer 1

Add the number of children as a integer on the comment field that gets updated every time a comment is added or removed. That way, you won't have to query for that value. You can do this using signals.
Add an ArrayField(if you're using postgres) or something similar on your Profile model that stores all the primary keys of Liked posts. Instead of querying the Likes model, you would be able to do this:
profile = Profile.objects.get(name='me')
liked = True if comment_pk in profile.liked_posts else False
Use select_related to CommentChildren instead of making an extra query for it.
Implementing these 3 items will get rid of all the db queries being executed in the "comment in comments.data" forloop which is probably taking up the majority of the processing time.
If you're interested, check out django-debug-toolbar which enables you to see what queries are being executed on every page.