application_controller.rb

  # Add this to your app/controllers/application_controller.rb

  # Log GC stats, if enabled (make this the first before_filter)
  before_filter :before_log_gc_stats

  # Log GC stats, if enabled (make this the last after_filter)
  after_filter :after_log_gc_stats

  def before_log_gc_stats
    return if (ENV['RUBY_GC_STATS'].nil? or ENV['RUBY_GC_STATS'] != '1')

    GC.log "***"
    GC.log "Request starting: " + request.url
    GC.log "***"
  end

  def after_log_gc_stats
    return if (ENV['RUBY_GC_STATS'].nil? or ENV['RUBY_GC_STATS'] != '1')

    GC.log "***"
    GC.log "Request completed: " + request.url
    GC.log "GC collections: " + GC.collections.to_s
    GC.log "GC time (us): " + GC.time.to_s
    GC.log "Bytes allocated since last GC run: " + GC.growth.to_s
    GC.log "Bytes allocated since last request: " + GC.allocated_size.to_s
    GC.log "Number of allocations since last request: " + GC.num_allocations.to_s
    GC.log "Live objects: " + ObjectSpace.live_objects.to_s
    GC.log "Total allocated objects since interpreter start: " + ObjectSpace.allocated_objects.to_s
    GC.dump
    GC.log "***"

    GC.clear_stats
  end

gc.rb

# Add this file to your config/initializers directory

# To enable logging of Ruby garbage collector and memory allocation stats
# with Ruby Enterprise Edition, set these environment variables:
#
# RUBY_GC_STATS=1
# RUBY_GC_DATA_FILE=/tmp/ruby_gc.txt

if !ENV['RUBY_GC_STATS'].nil? and ENV['RUBY_GC_STATS'] == '1' then
  GC.enable_stats
end