--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -89,14 +89,14 @@ module ApplicationHelper
   end
   
   def commit_graph_tag(repository, ref = "master")
-    filename = "#{repository.project.slug}_#{repository.name}_#{h(ref)}_commit_count.png"
+    filename = Gitorious::Graphs::CommitsBuilder.filename(repository, ref)
     if File.exist?(File.join(Gitorious::Graphs::Builder.graph_dir, filename))
       image_tag("graphs/#{filename}")
     end
   end
   
   def commit_graph_by_author_tag(repository, ref = "master")    
-    filename = "#{repository.project.slug}_#{repository.name}_#{h(ref)}_commit_count_by_author.png"
+    filename = Gitorious::Graphs::CommitsByAuthorBuilder.filename(repository, ref)
     if File.exist?(File.join(Gitorious::Graphs::Builder.graph_dir, filename))
       image_tag("graphs/#{filename}")
     end

--- a/lib/gitorious/graphs/builder.rb
+++ b/lib/gitorious/graphs/builder.rb
@@ -6,15 +6,26 @@ end
 
 module Gitorious
   module Graphs    
-    class Builder      
+    class Builder
+      GENERATORS = [CommitsBuilder, CommitsByAuthorBuilder] 
       def self.generate_all_for(repository)
-        CommitsBuilder.generate_for(repository)
-        CommitsByAuthorBuilder.generate_for(repository)
+        GENERATORS.each do |generator|
+          generator.generate_for(repository)
+        end
       end
       
       def self.graph_dir
         File.join(RAILS_ROOT, "public/images/graphs/")
       end
+      
+      def self.construct_filename(repository, branch, name)
+        "#{repository.project.slug}_#{repository.name}_#{branch}_#{name}.png"
+      end
+      
+      def self.status_file(repository, branch = "master")
+        File.join(RAILS_ROOT, "tmp", "graph_generator",
+             "#{repository.project.slug}_#{repository.name}_#{repository.git.commit_count(branch)}_#{self.name}.status")
+      end
 
       def self.default_theme
         {

--- a/lib/gitorious/graphs/commits_builder.rb
+++ b/lib/gitorious/graphs/commits_builder.rb
@@ -3,10 +3,15 @@ module Gitorious
     
     class CommitsBuilder < Gitorious::Graphs::Builder
       def self.generate_for(repository)
-        if repository.has_commits?
-          builder = new(repository, repository.head_candidate.name)
+        head = repository.head_candidate
+        return if head.nil?
+        
+        branch = head.name
+        if !File.exist?(self.status_file(repository, branch)) && repository.has_commits?
+          builder = new(repository, branch)
           builder.build
           builder.write
+          FileUtils.touch(self.status_file(repository, branch))
         end
       end
       
@@ -33,8 +38,12 @@ module Gitorious
         @graph.labels = build_labels(week_numbers)
       end
       
+      def self.filename(repository, branch)
+        Builder.construct_filename(repository, branch, "commit_count")
+      end
+      
       def construct_filename
-        "#{@repository.project.slug}_#{@repository.name}_#{@branch}_commit_count.png"
+        CommitsBuilder.filename(@repository, @branch)
       end
       
       private

--- a/lib/gitorious/graphs/commits_by_author_builder.rb
+++ b/lib/gitorious/graphs/commits_by_author_builder.rb
@@ -5,9 +5,13 @@ module Gitorious
       def self.generate_for(repository)
         if repository.has_commits?
           repository.git.heads.each do |head|
-            builder = new(repository, head.name)
-            builder.build
-            builder.write
+            branch = head.name
+            if !File.exist?(self.status_file(repository, branch))
+              builder = new(repository, branch)
+              builder.build
+              builder.write
+              FileUtils.touch(self.status_file(repository, branch))
+            end
           end
         end
       end
@@ -31,8 +35,12 @@ module Gitorious
         end
       end
       
+      def self.filename(repository, branch)
+        Builder.construct_filename(repository, branch, "commit_count_by_author")
+      end
+      
       def construct_filename
-        "#{@repository.project.slug}_#{@repository.name}_#{@branch}_commit_count_by_author.png"
+        CommitsByAuthorBuilder.filename(@repository, @branch)
       end
     end  
     

--- a/script/graph_generator
+++ b/script/graph_generator
@@ -1,5 +1,16 @@
 #!/usr/bin/env ruby
 
+require 'tmpdir'
+require "fileutils"
+
+LOCK_FILE_PATH = File.join(Dir.tmpdir, "gitorious_graphgenerator_lockfile")
+if File.exist?(LOCK_FILE_PATH)
+    $stderr.puts "Lockfile '#{LOCK_FILE_PATH}' exists!"
+    exit(1)
+end
+
+FileUtils.touch(LOCK_FILE_PATH)
+
 ENV["RAILS_ENV"] ||= "production"
 require File.dirname(__FILE__) + "/../config/environment"
 
@@ -8,6 +19,29 @@ log.formatter = Logger::Formatter.new
 log.level = Logger::INFO
 log.formatter.datetime_format = "%Y-%m-%d %H:%M:%S"
 
+STATUS_FILE = File.join(RAILS_ROOT, "tmp", "graph_generator.status")
+update_status = !File.exist?(STATUS_FILE)
+tmpdir = File.join(RAILS_ROOT, "tmp", "graph_generator")
+if !File.directory?(tmpdir)
+  FileUtils.mkdir_p(tmpdir)
+elsif !update_status
+  mtime = File.mtime(STATUS_FILE).utc
+
+  days = (Time.now.utc - mtime) / (3600*24)
+  if days >= 5
+    log.info "Cleaning '#{tmpdir}'..."
+    Dir.glob(File.join(tmpdir, "*.status")) do |file|
+      FileUtils.rm(file)
+    end
+
+    update_status = true
+  end
+end
+
+if update_status
+  FileUtils.touch(STATUS_FILE)
+end
+
 log.info "Starting graph generation run..."
 Repository.find(:all).each_with_index do |repository, index|
 	begin
@@ -25,4 +59,6 @@ Repository.find(:all).each_with_index do |repository, index|
 #    exit(1)		
 	end
 end
-log.info "Done with graph generation run"
\ No newline at end of file
+log.info "Done with graph generation run"
+
+FileUtils.rm(LOCK_FILE_PATH)