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The page "Example usages of DbUpdateNotification" has been deleted by JoanTouzet: https://wiki.apache.org/couchdb/Example%20usages%20of%20DbUpdateNotification?action=diff&rev1=12&rev2=13 Comment: This doesn't exist anymore - and 2.x has /_db_updates instead. - ## page was renamed from Regenerating_views_on_update - = Example usages of DbUpdateNotification = - == Update views on document save == - <<TableOfContents(3)>> - - CouchDB defaults to regenerating views the first time they are accessed. This behavior is preferable in most cases as it optimizes the resource utilization on the database server. - On the other hand, in some situations the benefit of always having fast and updated views far outweigh the cost of regenerating them every time the database server receives updates. This can be achieved by supplying an updater script that calls the views when needed. - - == Example using ruby == - - === couch.ini === - (0.8) Add the following line to the couch.ini file - {{{ - DbUpdateNotificationProcess=/PATH/TO/view_updater.rb - }}} - - (0.9+) Add the following section to the local.ini file: - {{{ - [update_notification] - view_updater=/PATH/TO/view_updater.rb - }}} - - === view_updater.rb === - The following script updates the views for each tenth update made to the database or at most once every second when a lot of saves are performed - - {{{#!highlight ruby - #!/usr/bin/ruby - - ################### - # 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"}} - - ################### - # 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, view| - `curl #{URL}/#{db_name}/_design/#{design}/_view/#{view}?limit=0` - 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 something 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} - - }}} - - The view_updater.rb itself has to be made executable by CouchDB (chmod 0700?). - - == Example using Python == - - {{{#!highlight python - - #!/usr/bin/env python - # -*- coding: utf-8 -*- - - """Updater script to regenerate couchdb views on update. - """ - - import logging - logging.basicConfig(level=logging.INFO) - - import os - import re - import signal - import sys - import time - import urllib2 - - from threading import Thread - - flags = { - 'is_running': True - } - - changed_docs = {} - - class ViewUpdater(object): - """Updates the views. - """ - - # The smallest amount of changed documents before the views are updated - MIN_NUM_OF_CHANGED_DOCS = 50 - - # Set the minimum pause between calls to the database - PAUSE = 5 # seconds - - # URL to the DB on the CouchDB server - URL = "http://localhost:5984"; - - # One entry for each design document - # in each database - VIEWS = { - 'my_db': { - 'design_doc': [ - 'view_name', - # ... - ] - } - } - - def start(self): - Thread(target=self._run).start() - - - def _run(self): - """Loop, checking for enough ``changed_docs`` to trigger a - request to couchdb to re-index. - """ - - while flags['is_running']: - try: - for db_name, number_of_docs in changed_docs.items(): - if number_of_docs >= self.MIN_NUM_OF_CHANGED_DOCS: - # Reset the value - del changed_docs[db_name] - # If there are views in the database, get them - if db_name in self.VIEWS: - logging.info('regenerating %s' % db_name) - db_views = self.VIEWS[db_name] - for design, views in db_views.iteritems(): - for view in views: - url = '%s/%s/_design/%s/_view/%s?limit=0' % ( - self.URL, db_name, design, view - ) - urllib2.urlopen(url) - time.sleep(self.PAUSE) - except: - flags['is_running'] = False - raise - - - - - - - - class NotificationConsumer(object): - """Receives the update notification from CouchDB. - """ - - DB_NAME_EXPRESSION = re.compile(r'\"db\":\"(\w+)\"') - - def _run(self): - """Consume update notifications from stdin. - """ - - while flags['is_running']: - try: - data = sys.stdin.readline() - except: - continue - else: - if not data: # exit - flags['is_running'] = False - break - result = self.DB_NAME_EXPRESSION.search(data) - if result: - db_name = result.group(1) - # Set to 0 if it hasn't been initialized before - if db_name not in changed_docs: - changed_docs[db_name] = 0 - # Add one pending changed document to the list - # of documents in the DB - changed_docs[db_name] += 1 - - - - - - - def start(self): - t = Thread(target=self._run) - t.start() - return t - - - - - - def main(): - logging.info('update_notification handler (re)starting') - consumer = NotificationConsumer() - updater = ViewUpdater() - updater.start() - t = consumer.start() - try: - while flags['is_running']: - t.join(10) - except KeyboardInterrupt, err: - flags['is_running'] = False - - - - - if __name__ == '__main__': - main() - - }}} -
