Distributed: support mget and mapped_mget

Map the keys to their nodes, mget them on each node, and stitch the
results together.

Author: jeremy

lib/redis/distributed.rb

@@ -279,11 +279,15 @@ def get(key)
 
     # Get the values of all the given keys.
     def mget(*keys)
-      raise CannotDistribute, :mget
+      mapped_mget(*keys).values_at(*keys)
     end
 
     def mapped_mget(*keys)
-      raise CannotDistribute, :mapped_mget
+      results = {}
+      keys.group_by { |k| node_for k }.each do |node, subkeys|
+        results.merge! node.mapped_mget(*subkeys)
+      end
+      results
     end
 
     # Overwrite part of a string at key starting at the specified offset.

test/distributed_commands_on_strings_test.rb

@@ -9,15 +9,27 @@ class TestDistributedCommandsOnStrings < Test::Unit::TestCase
   include Lint::Strings
 
   def test_mget
-    assert_raise Redis::Distributed::CannotDistribute do
-      r.mget("foo", "bar")
-    end
+    r.set("foo", "s1")
+    r.set("bar", "s2")
+
+    assert_equal ["s1", "s2"]     , r.mget("foo", "bar")
+    assert_equal ["s1", "s2", nil], r.mget("foo", "bar", "baz")
   end
 
   def test_mget_mapped
-    assert_raise Redis::Distributed::CannotDistribute do
-      r.mapped_mget("foo", "bar")
-    end
+    r.set("foo", "s1")
+    r.set("bar", "s2")
+
+    response = r.mapped_mget("foo", "bar")
+
+    assert_equal "s1", response["foo"]
+    assert_equal "s2", response["bar"]
+
+    response = r.mapped_mget("foo", "bar", "baz")
+
+    assert_equal "s1", response["foo"]
+    assert_equal "s2", response["bar"]
+    assert_equal nil , response["baz"]
   end
 
   def test_mset