diff --git a/src/lib_shell/mempool_worker.ml b/src/lib_shell/mempool_worker.ml
index e313d233d..ca7da1a97 100644
--- a/src/lib_shell/mempool_worker.ml
+++ b/src/lib_shell/mempool_worker.ml
@@ -62,7 +62,13 @@ module type T = sig
 
 end
 
-module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
+module type STATIC = sig
+  val max_size_parsed_cache: int
+end
+
+module Make(Static: STATIC)(Proto: Registered_protocol.T)
+  : T with module Proto = Proto
+= struct
 
   module Proto = Proto
 
@@ -221,32 +227,34 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
   (* parsed operations' cache. used for memoization *)
   module ParsedCache = struct
 
-    type t = operation tzresult Operation_hash.Table.t
+    type t = {
+      table: operation tzresult Operation_hash.Table.t ;
+      ring: Operation_hash.t Ring.t ;
+    }
 
-    let encoding =
-      (Operation_hash.Table.encoding
-         (Error_monad.result_encoding operation_encoding))
-
-    let create () : t =
-      Operation_hash.Table.create 1000
+    let create () : t = {
+      table = Operation_hash.Table.create Static.max_size_parsed_cache ;
+      ring = Ring.create Static.max_size_parsed_cache ;
+    }
 
     let add t raw_op parsed_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.replace t hash parsed_op
-
-    let mem t raw_op =
-      let hash = Operation.hash raw_op in
-      Operation_hash.Table.mem t hash
+      Option.iter
+        ~f:(Operation_hash.Table.remove t.table)
+        (Ring.add_and_return_erased t.ring hash);
+      Operation_hash.Table.replace t.table hash parsed_op
 
     let find_opt t raw_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.find_opt t hash
+      Operation_hash.Table.find_opt t.table hash
 
     let find_hash_opt t hash =
-      Operation_hash.Table.find_opt t hash
+      Operation_hash.Table.find_opt t.table hash
 
     let rem t hash =
-      Operation_hash.Table.remove t hash
+      (* NOTE: hashes are not removed from the ring. As a result, the cache size
+       * bound can be lowered. This is a non-issue because it's only a cache. *)
+      Operation_hash.Table.remove t.table hash
 
   end
 
diff --git a/src/lib_shell/mempool_worker.mli b/src/lib_shell/mempool_worker.mli
index be9fdd4a4..f5c33e8c9 100644
--- a/src/lib_shell/mempool_worker.mli
+++ b/src/lib_shell/mempool_worker.mli
@@ -63,5 +63,9 @@ module type T = sig
 
 end
 
-module Make (Proto : Registered_protocol.T) : T
+module type STATIC = sig
+  val max_size_parsed_cache: int
+end
+
+module Make (Static : STATIC) (Proto : Registered_protocol.T) : T with module Proto = Proto