couch_view_updater.rb

require 'rest_client'
require 'json'

###################
# CONF            #
###################

# The smallest amount of changed documents before the views are updated
MIN_NUM_OF_CHANGED_DOCS = 10

# URL to the DB on the CouchDB server
URL = "http://localhost:5984"

# Set the minimum pause between calls to the database
PAUSE = 1 # seconds

# One entry for each design document 
# in each database
#VIEWS = {"my_db"  => {"design_doc" => "view_name"}}

dbs = JSON.parse(RestClient.get("#{URL}/_all_dbs"))

VIEWS = {}

dbs_view = dbs.inject(VIEWS) do |views, db| 
  views[db] = {}
  designs = JSON.parse(RestClient.get("#{URL}/#{db}/_all_docs?startkey=%22_design%2F%22&endkey=%22_design0%22"))["rows"]
  designs.each do |design|
    design_url = "#{URL}/#{db}/#{design["id"]}"
    design_doc = JSON.parse(RestClient.get(design_url))
    design_dac_name = design_doc["_id"].gsub("_design/","")
    views[db][design_dac_name] = []
    design_doc["views"].each_key do |key|
      views[db][design_dac_name] << key
    end
  end 
  views
end

###################
# RUNTIME         #
###################

run = true
number_of_changed_docs = {}

threads = []

# Updates the views
threads << Thread.new do

  while run do

    number_of_changed_docs.each_pair do |db_name, number_of_docs|
      if number_of_docs >= MIN_NUM_OF_CHANGED_DOCS
        
        # Reset the value
        number_of_changed_docs[db_name] = 0
        
        # If there are views in the database, get them
        if VIEWS[db_name]
          VIEWS[db_name].each do |design, views|
            views.each do |view|
              `curl #{URL}/#{db_name}/_design/#{design}/_view/#{view}?limit=0`
            end
          end  
        end
                
      end
    end

    # Pause before starting over again
    sleep PAUSE
    
  end
  
end

# Receives the update notification from CouchDB
threads << Thread.new do

  while run do

    STDERR << "Waiting for input\n"
    update_call = gets
    
    # When CouchDB exits the script gets called with
    # a never ending series of nil
    if update_call == nil
      run = false
    else
      
      # Get the database name out of the call data
      # The data looks somethind like this:
      # {"type":"updated","db":"DB_NAME"}\n
      update_call =~ /\"db\":\"(\w+)\"/
      database_name = $1
      
      # Set to 0 if it hasn't been initialized before
      number_of_changed_docs[$1] ||= 0
      
      # Add one pending changed document to the list of documents
      # in the DB
      number_of_changed_docs[$1] += 1
      
    end
    
  end

end

# Good bye
threads.each {|thr| thr.join}