diff --git a/.gitignore b/.gitignore
index 111f8dea..a188004a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@ pkg/*
 tmp/*
 .*.sw[a-z]
 database.log
+.idea
diff --git a/lib/octopus.rb b/lib/octopus.rb
index 56f051a4..a8e47bce 100644
--- a/lib/octopus.rb
+++ b/lib/octopus.rb
@@ -6,26 +6,33 @@
 require 'erb'
 
 module Octopus
+  DEFAULT_ENVIRONMENTS = ['production']
+
   def self.env
+    return @env if @env
     @env ||= 'octopus'
   end
 
   def self.rails_env
+    return @rails_env if @rails_env
     @rails_env ||= defined?(::Rails.env) ? Rails.env.to_s : 'shards'
   end
 
   def self.config
-    @config ||= begin
+    return @config if @config
+
+    @config = begin
       file_name = File.join(Octopus.directory, 'config/shards.yml').to_s
 
       if File.exist?(file_name) || File.symlink?(file_name)
-        config ||= HashWithIndifferentAccess.new(YAML.load(ERB.new(File.read(file_name)).result))[Octopus.env]
-      else
-        config ||= HashWithIndifferentAccess.new
+        hash = HashWithIndifferentAccess.new(YAML.load(ERB.new(File.read(file_name)).result)) || HashWithIndifferentAccess.new
+        config ||= hash[Octopus.env]
       end
 
-      config
+      config ||= HashWithIndifferentAccess.new
     end
+
+    @config
   end
 
   def self.load_balancer=(balancer)
@@ -33,6 +40,7 @@ def self.load_balancer=(balancer)
   end
 
   def self.load_balancer
+    return @load_balancer if @load_balancer
     @load_balancer ||= Octopus::LoadBalancing::RoundRobin
   end
 
@@ -58,6 +66,7 @@ def self.enabled?
   # Returns the Rails.root_to_s when you are using rails
   # Running the current directory in a generic Ruby process
   def self.directory
+    return @directory if @directory
     @directory ||= defined?(::Rails.root) ? Rails.root.to_s : Dir.pwd
   end
 
@@ -73,7 +82,15 @@ def self.environments=(environments)
   end
 
   def self.environments
-    @environments ||= config['environments'] || ['production']
+    return @environments if @environments
+
+    if config
+      environments = (config['environments'] || [])
+    else
+      environments = []
+    end
+
+    @environments = environments.compact.uniq
   end
 
   def self.robust_environments=(environments)
@@ -83,7 +100,15 @@ def self.robust_environments=(environments)
   # Environments in which to swallow failures from a single shard
   # when iterating through all.
   def self.robust_environments
-    @robust_environments ||= config['robust_environments'] || ['production']
+    return @robust_environments if @robust_environments
+
+    if config
+      robust_environments = (config['robust_environments'] || []) + DEFAULT_ENVIRONMENTS
+    else
+      robust_environments = DEFAULT_ENVIRONMENTS
+    end
+
+    @robust_environments = robust_environments.compact.uniq
   end
 
   def self.robust_environment?
@@ -105,11 +130,15 @@ def self.rails41?
   attr_writer :logger
 
   def self.logger
+    return @logger if @logger
+
     if defined?(Rails.logger)
-      @logger ||= Rails.logger
+      @logger = Rails.logger
     else
-      @logger ||= Logger.new($stderr)
+      @logger = Logger.new($stderr)
     end
+
+    @logger
   end
 
   def self.shards=(shards)
diff --git a/lib/octopus/load_balancing/round_robin.rb b/lib/octopus/load_balancing/round_robin.rb
index a1673417..ed4a550c 100644
--- a/lib/octopus/load_balancing/round_robin.rb
+++ b/lib/octopus/load_balancing/round_robin.rb
@@ -1,4 +1,5 @@
 require 'octopus/load_balancing'
+require 'thread'
 
 # The round-robin load balancing of slaves belonging to the same shard.
 # It is a pool that contains slaves which queries are distributed to.
@@ -8,11 +9,14 @@ class RoundRobin
       def initialize(slaves_list)
         @slaves_list = slaves_list
         @slave_index = 0
+        @semaphore = Mutex.new
       end
 
       # Returns the next available slave in the pool
       def next(options)
-        @slaves_list[@slave_index = (@slave_index + 1) % @slaves_list.length]
+        @semaphore.synchronize {
+          @slaves_list[@slave_index = (@slave_index + 1) % @slaves_list.length]
+        }
       end
     end
   end
diff --git a/lib/octopus/proxy.rb b/lib/octopus/proxy.rb
index c3bac619..bc5a9881 100644
--- a/lib/octopus/proxy.rb
+++ b/lib/octopus/proxy.rb
@@ -34,7 +34,6 @@ def initialize_shards(config)
       end
 
       @shards_config ||= []
-
       @shards_config.each do |key, value|
         if value.is_a?(String)
           value = resolve_string_connection(value).merge(:octopus_shard => key)
@@ -86,7 +85,12 @@ def initialize_shards(config)
     end
 
     def initialize_replication(config)
-      @replicated = true
+      if config.key?('replicated')
+        @replicated = config['replicated']
+      else
+        @replicated = true
+      end
+
       if config.key?('fully_replicated')
         @fully_replicated = config['fully_replicated']
       else
@@ -190,7 +194,8 @@ def last_current_shard=(last_current_shard)
     end
 
     def fully_replicated?
-      @fully_replicated || Thread.current[FULLY_REPLICATED_KEY]
+      return @fully_replicated if Thread.current[FULLY_REPLICATED_KEY].nil?
+      Thread.current[FULLY_REPLICATED_KEY]
     end
 
     # Public: Whether or not a group exists with the given name converted to a
@@ -293,12 +298,16 @@ def method_missing(method, *args, &block)
         self.last_current_shard = current_shard
         clean_connection_proxy
         conn.send(method, *args, &block)
-      elsif should_send_queries_to_shard_slave_group?(method)
-        send_queries_to_shard_slave_group(method, *args, &block)
-      elsif should_send_queries_to_slave_group?(method)
-        send_queries_to_slave_group(method, *args, &block)
-      elsif should_send_queries_to_replicated_databases?(method)
-        send_queries_to_selected_slave(method, *args, &block)
+      elsif method_contains_select?(method)
+        if should_send_queries_to_shard_slave_group?(method)
+          send_queries_to_shard_slave_group(method, *args, &block)
+        elsif should_send_queries_to_slave_group?(method)
+          send_queries_to_slave_group(method, *args, &block)
+        elsif should_send_queries_to_replicated_databases?(method)
+          send_queries_to_selected_slave(method, *args, &block)
+        else
+          select_connection.send(method, *args, &block)
+        end
       else
         select_connection.send(method, *args, &block)
       end
@@ -426,13 +435,17 @@ def resolve_string_connection(spec)
       end
     end
 
+    def method_contains_select?(method)
+      !(method.to_s =~ /select/).nil?
+    end
+
     def should_clean_connection_proxy?(method)
-      method.to_s =~ /insert|select|execute/ && !current_model_replicated? && (!block || block != current_shard)
+      !(method.to_s =~ /insert|select|execute/).nil? && !current_model_replicated? && (!block || block != current_shard)
     end
 
     # Try to use slaves if and only if `replicated: true` is specified in `shards.yml` and no slaves groups are defined
     def should_send_queries_to_replicated_databases?(method)
-      @replicated && method.to_s =~ /select/ && !block && !slaves_grouped?
+      @replicated && !block && !slaves_grouped?
     end
 
     def current_model_replicated?
@@ -459,11 +472,11 @@ def send_queries_to_selected_slave(method, *args, &block)
     # while ensuring that we revert `current_shard` from the selected slave to the (shard's) master
     # not to make queries other than SELECT leak to the slave.
     def should_use_slaves_for_method?(method)
-      current_model_replicated? && method.to_s =~ /select/
+      current_model_replicated?
     end
 
     def slaves_grouped?
-      @slave_groups.present?
+      current_group && @slave_groups[current_group]
     end
 
     # Temporarily switch `current_shard` to the next slave in a slave group and send queries to it
@@ -501,7 +514,6 @@ def using_shard(shard, &_block)
       older_slave_group = current_slave_group
       older_load_balance_options = current_load_balance_options
 
-
       begin
         unless current_model && !current_model.allowed_shard?(shard)
           self.current_shard = shard
diff --git a/spec/octopus/octopus_spec.rb b/spec/octopus/octopus_spec.rb
index b931ece8..97b7d6ae 100644
--- a/spec/octopus/octopus_spec.rb
+++ b/spec/octopus/octopus_spec.rb
@@ -49,7 +49,7 @@
 
   describe '#setup' do
     it 'should have the default octopus environment as production' do
-      expect(Octopus.environments).to eq(['production'])
+      expect(Octopus.environments).to eq([])
     end
 
     it 'should allow the user to configure the octopus environments' do
diff --git a/spec/octopus/replicated_slave_grouped_spec.rb b/spec/octopus/replicated_slave_grouped_spec.rb
index 49148cb7..6d5918f3 100644
--- a/spec/octopus/replicated_slave_grouped_spec.rb
+++ b/spec/octopus/replicated_slave_grouped_spec.rb
@@ -54,11 +54,13 @@
       # In `database.yml` and `shards.yml`, we have configured 1 master and 4 slaves.
       # So we can ensure Octopus is not distributing queries between them
       # by asserting 1 + 4 = 5 queries go to :master(`octopus_shard_1`)
-      expect(Cat.count).to eq(2)
-      expect(Cat.count).to eq(2)
-      expect(Cat.count).to eq(2)
-      expect(Cat.count).to eq(2)
-      expect(Cat.count).to eq(2)
+      Octopus.using(:master) do
+        expect(Cat.count).to eq(2)
+        expect(Cat.count).to eq(2)
+        expect(Cat.count).to eq(2)
+        expect(Cat.count).to eq(2)
+        expect(Cat.count).to eq(2)
+      end
     end
   end
 
@@ -74,7 +76,7 @@
       end
     end
   end
-  
+
   it 'should restore previous slave group after a using block' do
     OctopusHelper.using_environment :replicated_slave_grouped do
       Cat.create!(:name => 'Thiago1')