We can do that by typing the following in the console (remember to reload!)

>> ActiveRecord::Base.logger = Logger.new(STDOUT)

But what if we want to turn this off? Just set the logger to nil. (then reload!) Here are two methods that will help automate this feature. Place them in your .irbrc file

require 'logger'

def logger_on
  set_logger_to Logger.new(STDOUT)
end

def logger_off
  set_logger_to nil
end

def set_logger_to(logger)
  ActiveRecord::Base.logger = logger
  reload!
end

Then you can just type logger_on to turn on SQL logging, or logger_off to turn it off.

If you want to have colors in your console, install the wirble gem (Read the documentation).

For some reason, I can't override the colors when I follow the instructions in the README. In case someone's also experiencing this, you can try merging the colors in the Wirble::Colorize::DEFAULT_COLORS constant. Then call the init and colorize methods.

Here's mine (same as with vim's syntax highlighting for ruby and haml).

Wirble::Colorize::DEFAULT_COLORS.merge!({
  # delimiter colors
  :comma => :none,
  :refers => :none,

  # container colors (hash and array)
  :open_hash => :purple,
  :close_hash => :purple,
  :open_array => :purple,
  :close_array => :purple,

  # object colors
  :open_object => :light_red,
  :object_class => :white,
  :object_addr_prefix => :blue,
  :object_line_prefix => :blue,
  :close_object => :light_red,

  # symbol colors
  :symbol => :red,
  :symbol_prefix => :red,

  # string colors
  :open_string => :purple,
  :string => :red,
  :close_string => :purple,

  # misc colors
  :number => :red,
  :keyword => :brown,
  :class => :green,
  :range => :none
})

I've been using some simple fragment caching on some of the pages of my current app.  But one update made all these fragments expire.  So either I create a rake task to delete these cache fragments or I use the console. Either way, the only thing you need to remember is

ActionController::Base.new.expire_fragment(key)

Of course, almost all of the times, key is dynamic. But since key accepts either a String, Hash or Regexp, this shouldn't be a problem. Check the fragment caching module