Welcome,

I need some advise to improve perfomence my web application.

In the begin I had this structure of database:

USER

-id (Primary Key)

-name

-password

-email ....

PROFILE

-user Primary Key, Foreign Key (USER)

-birthday

-region

-photoFile ...

PAGES

-id (Primary Key)

-user Foreign Key(USER)

-page

-date

COMMENTS

-id (Primary Key)

-user Foreign Key(USER)

-page Foreign Key(PAGE)

-comment

-date

FAVOURITES_PAGES

-id (Primary Key)

-user Foreign Key(USER)

-favourite_page Foreign Key(PAGE)

-date

but now one of the most important page of website is observatory, when everyone can observe activity others users. So I need select all pages, comments and favourites pages some users and display it in one list, sorted by date.

For better perfomance (I think) I changed my structure to this:

table USER and PROFILE without changes

ACTIVITY (additional table- have common fields: user,date) 
-id (Primary Key)
-user Foreign Key(USER)
-date
-page Foreign Key(PAGE)
-comment Foreign Key(COMMENTS)
-favourite_page Foreign Key(FAVOURITES_PAGES)


PAGES
-id (Primary Key)
-page

COMMENTS
-id (Primary Key)
-page Foreign Key(PAGE)
-comment

FAVOURITES_PAGES
-id (Primary Key)
-favourite_page Foreign Key(PAGE)

So now it is very easy get sorted records from all tables. But I have no only foreign key to PAGES, COMMENTS and FAVOURITES_PAGES in ACTIVITY table - there is about ten Foreign Key fields and in one record only one have value, others have None:

ACTIVITY
id    user     date page comment ...
1    2 2010-02-23 None     1
2    1 2010-02-21 1         None
....

It is corect solution. When I display about 40 records in one page (pagination) I must wait about one secound, but database is almost emty (a few users and about 100 records in others tables). It is depends on amount records per page - I have checked it, but why it takes too long time, becouse of relationships?

The website is built in Python/Django.

Any advices/opinion?