Cache: write_multi (#29366)

Rails.cache.write_multi foo: 'bar', baz: 'qux'

Plus faster `fetch_multi` with stores that implement `write_multi_entries`.
Keys that aren't found may be written to the cache store in one shot
instead of separate writes.

The default implementation simply calls `write_entry` for each entry.
Stores may override if they're capable of one-shot bulk writes, like
Redis `MSET`.

3 files changed, 100 insertions, 6 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index fc1e5516f8..d1d61ac8d7 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,17 @@
+*   Cache: `write_multi`
+
+        Rails.cache.write_multi foo: 'bar', baz: 'qux'
+
+    Plus faster fetch_multi with stores that implement `write_multi_entries`.
+    Keys that aren't found may be written to the cache store in one shot
+    instead of separate writes.
+
+    The default implementation simply calls `write_entry` for each entry.
+    Stores may override if they're capable of one-shot bulk writes, like
+    Redis `MSET`.
+
+    *Jeremy Daer*
+
 *   Add default option to module and class attribute accessors.
 
         mattr_accessor :settings, default: {}
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index a1093a2e23..fa487060e2 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -373,6 +373,19 @@ module ActiveSupport
         results
       end
 
+      # Cache Storage API to write multiple values at once.
+      def write_multi(hash, options = nil)
+        options = merged_options(options)
+
+        instrument :write_multi, hash, options do |payload|
+          entries = hash.each_with_object({}) do |(name, value), memo|
+            memo[normalize_key(name, options)] = Entry.new(value, options.merge(version: normalize_version(name, options)))
+          end
+
+          write_multi_entries entries, options
+        end
+      end
+
       # Fetches data from the cache, using the given keys. If there is data in
       # the cache with the given keys, then that data is returned. Otherwise,
       # the supplied block is called for each key for which there was no data,
@@ -397,14 +410,15 @@ module ActiveSupport
 
         options = names.extract_options!
         options = merged_options(options)
-        results = read_multi(*names, options)
 
-        names.each_with_object({}) do |name, memo|
-          memo[name] = results.fetch(name) do
-            value = yield name
-            write(name, value, options)
-            value
+        read_multi(*names, options).tap do |results|
+          writes = {}
+
+          (names - results.keys).each do |name|
+            results[name] = writes[name] = yield(name)
           end
+
+          write_multi writes, options
         end
       end
 
@@ -521,6 +535,14 @@ module ActiveSupport
           raise NotImplementedError.new
         end
 
+        # Writes multiple entries to the cache implementation. Subclasses MAY
+        # implement this method.
+        def write_multi_entries(hash, options)
+          hash.each do |key, entry|
+            write_entry key, entry, options
+          end
+        end
+
         # Deletes an entry from the cache implementation. Subclasses must
         # implement this method.
         def delete_entry(key, options)
diff --git a/activesupport/test/caching_test.rb b/activesupport/test/caching_test.rb
index f53b98c73e..f2f8c58111 100644
--- a/activesupport/test/caching_test.rb
+++ b/activesupport/test/caching_test.rb
@@ -1299,3 +1299,61 @@ class CacheEntryTest < ActiveSupport::TestCase
     assert_equal value.bytesize, entry.size
   end
 end
+
+class CacheStoreWriteMultiEntriesStoreProviderInterfaceTest < ActiveSupport::TestCase
+  setup do
+    @cache = ActiveSupport::Cache.lookup_store(:null_store)
+  end
+
+  test "fetch_multi uses write_multi_entries store provider interface" do
+    assert_called_with(@cache, :write_multi_entries) do
+      @cache.fetch_multi "a", "b", "c" do |key|
+        key * 2
+      end
+    end
+  end
+end
+
+class CacheStoreWriteMultiInstrumentationTest < ActiveSupport::TestCase
+  setup do
+    @cache = ActiveSupport::Cache.lookup_store(:null_store)
+  end
+
+  test "instrumentation" do
+    writes = { "a" => "aa", "b" => "bb" }
+
+    events = with_instrumentation "write_multi" do
+      @cache.write_multi(writes)
+    end
+
+    assert_equal %w[ cache_write_multi.active_support ], events.map(&:name)
+    assert_nil events[0].payload[:super_operation]
+    assert_equal({ "a" => "aa", "b" => "bb" }, events[0].payload[:key])
+  end
+
+  test "instrumentation with fetch_multi as super operation" do
+    skip "fetch_multi isn't instrumented yet"
+
+    events = with_instrumentation "write_multi" do
+      @cache.fetch_multi("a", "b") { |key| key * 2 }
+    end
+
+    assert_equal %w[ cache_write_multi.active_support ], events.map(&:name)
+    assert_nil events[0].payload[:super_operation]
+    assert !events[0].payload[:hit]
+  end
+
+  private
+    def with_instrumentation(method)
+      event_name = "cache_#{method}.active_support"
+
+      [].tap do |events|
+        ActiveSupport::Notifications.subscribe event_name do |*args|
+          events << ActiveSupport::Notifications::Event.new(*args)
+        end
+        yield
+      end
+    ensure
+      ActiveSupport::Notifications.unsubscribe event_name
+    end
+end