Archive for March 2010
Caching in Rails with memcached
Posted on: March 27, 2010
Installation
1. Follow this link to download and install memcached.
2. Start the memcached server using either
memcached -vv
or
/etc/init.d/memcached start
Integrating memcached with your rails application.
1. Install memcache-client
gem install memcache-client
2. Add the below line to end of your config/environment.rb file.
CACHE = MemCache.new('127.0.0.1')
3. Add the following method to your application controller / application helper or where ever you want according to your need.
def perform_cache(key)
begin
unless output = CACHE.get(key)
output = yield
CACHE.set(key, output, 15.minutes)
end
rescue => e
logger.info “MEMCACHE ERROR++++++++++++++++++++++++++++++++++++”
logger.info “ERROR : #{e.message}”
logger.info “MEMCACHE ERROR++++++++++++++++++++++++++++++++++++”
output = yield
end
return output
end
The above method performs the caching based on a unique key. If the value for that key already exists, it will return the output from the stored cache or else it will execute the block you are using when calling the above method and generate a new value from the executed block for the particular key and store it in the cache.
You can set a timer to expire the cached data.(15 mins in my case.)
If you don’t want to expire the cache based on timer, simply remove the third parameter we are passing to ’set’ method.
The above method also handles the exception,in case your memcache server is down for some reason.
4. Cache your complex queries/methods as follows.
my_key = Digest::MD5.hexdigest(request.request_uri)
output = perform_cache(my_key) { ClassName.method_name(…) }
Note : The key generated should be always unique, otherwise it will overwrite your existing cached data already having the same key. I am using the URL as the key, Since the URL is pretty long we can take the MD5 hash/SHA1 hash of it and use it as the key.
5. You can edit memory used by memcached as follows.
Open /etc/sysconfig/memcached file and edit “CACHESIZE” entry,
this entry is in MBs.
That's it your ready to go.
Rails crontab with “whenever” gem
Posted on: March 27, 2010
- In: rails | ruby on rails
- 4 Comments
Introduction
gem “whenever“ provides you with the valid cronjob syntax and also writes / updates the crontab file for you.
Installation
1. Install the gem
gem install whenever
2. Add below line to your config/environment.rb
config.gem ‘whenever’, :lib=>false, :source=>’http://gemcutter.org’
3. Go to your application root directory and run the below command
wheneverize .
This will create a “config/schedule.rb” file for you. EXAMPLE “config/schedule.rb” set :environment, :development set :path, "/var/www/MyApp" # Scheduled Hourly every 4.hours do command "/usr/bin/your_command" end # Scheduled Daily every 1.day, :at => '12:00 am' do runner "MyModel.yourmethod" end # Scheduled Weekly every :monday, :at => '11:00 pm' do rake "your:rake:task" end
Consider the above as the contents of your config/schedule.rb file.
4. Now from application root directory, run the below command
whenever
The above command will output valid syntax for the crontab as below.
0 0 * * * /var/www/MyApp/script/runner -e development “Model.your_method” 0 0,4,8,12,16,20 * * * /usr/bin/your_command 0 23 * * 1 cd /var/www/MyApp && RAILS_ENV=development /usr/bin/env rake your:rake_task
5. Now, To write the above content in your Crontab file run the below command.
whenever –update-crontab
you can see the above entries in your crontab file by running “crontab -e”.
That’s it, you are ready to go.
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