How to correctly count occurrences of a string in a string with Ruby

I have a 300 MB text file, I want to count the occurrences of every 10,000 substrings in the file. I want to know how to do it quickly.

Now I use the following code:

content = IO.read("path/to/mytextfile")
Word.each do |w|
  w.occurrence = content.scan(w.name).size
  w.save
end

A word is an ActiveRecord class.

It took me almost 1 day to finish the count. Is there any way to make this faster? Thank.

Edit1: Thanks again. I run the rails 2.3.9. The table namecontained in the word table contains what I am looking for and contains only unique values. Instead of using, Word.eachI use loading (1000 lines per second). This should help.

I rewrote all the code with an idea from bpaulon. Now it took only a few hours to complete the count.

, utf8 encode

def truncate(n)
  self.slice(/\A.{0,#{n}}/m)
end

def utf8_length
  self.unpack('U*').size
end

?