Merge pull request #11546 from swoop-inc/ss_memory_store_cache_size

[Fixes #11512] improves cache size calculation in MemoryStore

1 files changed, 14 insertions, 3 deletions

diff --git a/activesupport/lib/active_support/cache/memory_store.rb b/activesupport/lib/active_support/cache/memory_store.rb
index e58b7be9f8..b979521c99 100644
--- a/activesupport/lib/active_support/cache/memory_store.rb
+++ b/activesupport/lib/active_support/cache/memory_store.rb
@@ -123,6 +123,14 @@ module ActiveSupport
       end
 
       protected
+
+        # See https://gist.github.com/ssimeonov/6047200
+        PER_ENTRY_OVERHEAD = 240
+
+        def cached_size(key, entry)
+          key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
+        end
+
         def read_entry(key, options) # :nodoc:
           entry = @data[key]
           synchronize do
@@ -140,8 +148,11 @@ module ActiveSupport
           synchronize do
             old_entry = @data[key]
             return false if @data.key?(key) && options[:unless_exist]
-            @cache_size -= old_entry.size if old_entry
-            @cache_size += entry.size
+            if old_entry
+              @cache_size -= (old_entry.size - entry.size)
+            else
+              @cache_size += cached_size(key, entry)
+            end
             @key_access[key] = Time.now.to_f
             @data[key] = entry
             prune(@max_size * 0.75, @max_prune_time) if @cache_size > @max_size
@@ -153,7 +164,7 @@ module ActiveSupport
           synchronize do
             @key_access.delete(key)
             entry = @data.delete(key)
-            @cache_size -= entry.size if entry
+            @cache_size -= cached_size(key, entry) if entry
             !!entry
           end
         end