How to store all user activites in a website..?
In your log table you can have various columns, including:

user_id (the user that did the action)
activity_type (the type of activity, such as view or commented_on)
object_id (the actual object that it concerns, such as the Article or Media)
object_type (the type of object; this can be used later, in combination with object_id to lookup the object in the database)

This way, you can keep track of all actions the users do. You'd need to update this table whenever something happens that you wish to track.
I have a web application build in Django + Python that interact with web services (written in JAVA).
Now all the database management part is done by web-services i.e. all CRUD operations to actual database is done by web-services.

Now i have to track all User Activities done on my website in some log table.
Like If User posted a new article, then a new row is created into Articles table by web-services and side by side, i need to add a new row into log table , something like "User : Raman has posted a new article (with ID, title etc)"
I have to do this for all Objects in my database like "Article", "Media", "Comments" etc

Note : I am using PostgreSQL

So what is the best way to achieve this..?? (Should I do it in PostgreSQL OR JAVA ..??..And How..??)