Revert "Instrument read_multi".

Reevaluating the log output generated from this instrumentation,
we've found that it wasn't all that useful in practice.

```
Caches multi read:
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/2/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad
- views/david/3/4184ab71db6849621a4d8820fcd2c0ad
```

If rendering many templates the output is inscrutable, and it's impossible
to see how many cache misses there were.

Revert ca6aba7f30 and implement a better way later.

3 files changed, 17 insertions, 41 deletions

diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index 610105f41c..1c63e8a93f 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -333,21 +333,19 @@ module ActiveSupport
         options = names.extract_options!
         options = merged_options(options)
 
-        instrument_multi(:read, names, options) do |payload|
-          results = {}
-          names.each do |name|
-            key = normalize_key(name, options)
-            entry = read_entry(key, options)
-            if entry
-              if entry.expired?
-                delete_entry(key, options)
-              else
-                results[name] = entry.value
-              end
+        results = {}
+        names.each do |name|
+          key = normalize_key(name, options)
+          entry = read_entry(key, options)
+          if entry
+            if entry.expired?
+              delete_entry(key, options)
+            else
+              results[name] = entry.value
             end
           end
-          results
         end
+        results
       end
 
       # Fetches data from the cache, using the given keys. If there is data in
@@ -555,17 +553,6 @@ module ActiveSupport
           ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload){ yield(payload) }
         end
 
-        def instrument_multi(operation, keys, options = nil)
-          log do
-            formatted_keys = keys.map { |k| "- #{k}" }.join("\n")
-            "Caches multi #{operation}:\n#{formatted_keys}#{options.blank? ? "" : " (#{options.inspect})"}"
-          end
-
-          payload = { key: keys }
-          payload.merge!(options) if options.is_a?(Hash)
-          ActiveSupport::Notifications.instrument("cache_#{operation}_multi.active_support", payload) { yield(payload) }
-        end
-
         def log
           return unless logger && logger.debug? && !silence?
           logger.debug(yield)
diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index 174913365a..2ca4b51efa 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -96,16 +96,14 @@ module ActiveSupport
         options = names.extract_options!
         options = merged_options(options)
 
-        instrument_multi(:read, names, options) do
-          keys_to_names = Hash[names.map{|name| [normalize_key(name, options), name]}]
-          raw_values = @data.get_multi(keys_to_names.keys, :raw => true)
-          values = {}
-          raw_values.each do |key, value|
-            entry = deserialize_entry(value)
-            values[keys_to_names[key]] = entry.value unless entry.expired?
-          end
-          values
+        keys_to_names = Hash[names.map{|name| [normalize_key(name, options), name]}]
+        raw_values = @data.get_multi(keys_to_names.keys, :raw => true)
+        values = {}
+        raw_values.each do |key, value|
+          entry = deserialize_entry(value)
+          values[keys_to_names[key]] = entry.value unless entry.expired?
         end
+        values
       end
 
       # Increment a cached value. This method uses the memcached incr atomic
diff --git a/activesupport/test/caching_test.rb b/activesupport/test/caching_test.rb
index 4a299429f3..39fa3cedbe 100644
--- a/activesupport/test/caching_test.rb
+++ b/activesupport/test/caching_test.rb
@@ -1151,15 +1151,6 @@ class CacheStoreLoggerTest < ActiveSupport::TestCase
     @cache.mute { @cache.fetch('foo') { 'bar' } }
     assert @buffer.string.blank?
   end
-
-  def test_multi_read_loggin
-    @cache.write 'hello', 'goodbye'
-    @cache.write 'world', 'earth'
-
-    @cache.read_multi('hello', 'world')
-
-    assert_match "Caches multi read:\n- hello\n- world", @buffer.string
-  end
 end
 
 class CacheEntryTest < ActiveSupport::TestCase