Get Redis database usage (per database)

redis-database-usage.rb

require 'redis' # gem install redis (4.8.x in my case)

15.times.each do |db|
  redis = Redis.new(url: "redis://localhost/#{db}") # or whatever

  total = 0
  redis.scan_each.each do |key|
    size = redis.send(:send_command, [:memory, :usage, key])
    total += size
    # puts " DB#{db} #{key} => #{size}b"
  end
  puts "DB#{db} total: #{total/1024/1024}M"
end