Does it has a way to compact the database size?

Dear All,

 

I use PostgreSQL 8.0.3 for store my data started on Sep'06. Today, I use database_size('name') function for checking my database size and found that it's about 1209715345.

 

I think that something maybe wrong on my database because I backup my database everyday and the backup size is about 10 MB.  So I restore databse from my backup file then use database_size('name') function again and found that  database size is about 56642193.

 

I can said both 1209715345 and 56642193 are coming from the same database but I wonder that why it quiet difference on size.

 

Any Idea?

And How can I control or compact my database size for make it smallest as possibled?