buffer: Do more precise timekey optimization handling. Fix #3088

lib/fluent/plugin/buffer.rb

@@ -143,17 +143,33 @@ def <=>(o)
           end
         end
 
+        # timekey should be unixtime as usual.
+        # So, unixtime should be bigger than 2^30 - 1 (= 1073741823) nowadays.
+        # We should check object_id stability to use object_id as optimization for comparing operations.
+        # e.g.)
+        # irb> Time.parse("2020/07/31 18:30:00+09:00").to_i
+        # => 1596187800
+        # irb> Time.parse("2020/07/31 18:30:00+09:00").to_i > 2**30 -1
+        # => true
+        def self.enable_optimize?
+          a1 = 2**30 - 1
+          a2 = 2**30 - 1
+          b1 = 2**62 - 1
+          b2 = 2**62 - 1
+          (a1.object_id == a2.object_id) && (b1.object_id == b2.object_id)
+        end
+
         # This is an optimization code. Current Struct's implementation is comparing all data.
         # https://github.com/ruby/ruby/blob/0623e2b7cc621b1733a760b72af246b06c30cf96/struct.c#L1200-L1203
         # Actually this overhead is very small but this class is generated *per chunk* (and used in hash object).
         # This means that this class is one of the most called object in Fluentd.
         # See https://github.com/fluent/fluentd/pull/2560
-        # But, this optimization has a side effect on Windows due to differing object_id.
+        # But, this optimization has a side effect on Windows and 32bit environment(s) due to differing object_id.
         # This difference causes flood of buffer files.
-        # So, this optimization should be enabled on non-Windows platform.
+        # So, this optimization should be enabled on `enable_optimize?` as true platforms.
         def hash
           timekey.object_id
-        end unless Fluent.windows?
+        end if enable_optimize?
       end
 
       # for tests