Cache: Enable compression by default for values > 1kB.

Compression has long been available, but opt-in and at a 16kB threshold.
It wasn't enabled by default due to CPU cost. Today it's cheap and
typical cache data is eminently compressible, such as HTML or JSON
fragments.

Compression dramatically reduces Memcached/Redis mem usage, which means
the same cache servers can store more data, which means higher hit
rates.

To disable compression, pass `compress: false` to the initializer.

2 files changed, 20 insertions, 3 deletions

diff --git a/activesupport/test/cache/behaviors/cache_store_behavior.rb b/activesupport/test/cache/behaviors/cache_store_behavior.rb
index 582e902f72..73a9b2a71c 100644
--- a/activesupport/test/cache/behaviors/cache_store_behavior.rb
+++ b/activesupport/test/cache/behaviors/cache_store_behavior.rb
@@ -146,6 +146,16 @@ module CacheStoreBehavior
     assert_nil @cache.read("foo")
   end
 
+  def test_read_and_write_uncompressed_small_data
+    @cache.write("foo", "bar", compress: false)
+    assert_equal "bar", @cache.read("foo")
+  end
+
+  def test_read_and_write_uncompressed_nil
+    @cache.write("foo", nil, compress: false)
+    assert_nil @cache.read("foo")
+  end
+
   def test_cache_key
     obj = Object.new
     def obj.cache_key
diff --git a/activesupport/test/cache/cache_entry_test.rb b/activesupport/test/cache/cache_entry_test.rb
index 51b214ad8f..80ff7ad564 100644
--- a/activesupport/test/cache/cache_entry_test.rb
+++ b/activesupport/test/cache/cache_entry_test.rb
@@ -14,16 +14,23 @@ class CacheEntryTest < ActiveSupport::TestCase
     end
   end
 
-  def test_compress_values
+  def test_compressed_values
     value = "value" * 100
     entry = ActiveSupport::Cache::Entry.new(value, compress: true, compress_threshold: 1)
     assert_equal value, entry.value
     assert(value.bytesize > entry.size, "value is compressed")
   end
 
-  def test_non_compress_values
+  def test_compressed_by_default
     value = "value" * 100
-    entry = ActiveSupport::Cache::Entry.new(value)
+    entry = ActiveSupport::Cache::Entry.new(value, compress_threshold: 1)
+    assert_equal value, entry.value
+    assert(value.bytesize > entry.size, "value is compressed")
+  end
+
+  def test_uncompressed_values
+    value = "value" * 100
+    entry = ActiveSupport::Cache::Entry.new(value, compress: false)
     assert_equal value, entry.value
     assert_equal value.bytesize, entry.size
   end