Revert "Increase the number of unique bits for actors to avoid handle collisions (#12894)" (#12988)

This reverts commit 3e492a79ec.

src/ray/common/constants.h

@@ -18,7 +18,7 @@
 #include <stdint.h>
 
 /// Length of Ray full-length IDs in bytes.
-constexpr size_t kUniqueIDSize = 28;
+constexpr size_t kUniqueIDSize = 20;
 
 /// An ObjectID's bytes are split into the task ID itself and the index of the
 /// object's creation. This is the maximum width of the object index in bits.

src/ray/common/id.h

@@ -124,7 +124,7 @@ class JobID : public BaseID<JobID> {
 
 class ActorID : public BaseID<ActorID> {
  private:
-  static constexpr size_t kUniqueBytesLength = 12;
+  static constexpr size_t kUniqueBytesLength = 4;
 
  public:
   /// Length of `ActorID` in bytes.

src/ray/core_worker/actor_manager.cc

@@ -91,8 +91,6 @@ bool ActorManager::AddActorHandle(std::unique_ptr<ActorHandle> actor_handle,
                   std::placeholders::_1, std::placeholders::_2);
     RAY_CHECK_OK(gcs_client_->Actors().AsyncSubscribe(
         actor_id, actor_notification_callback, nullptr));
-  } else {
-    RAY_LOG(ERROR) << "Actor handle already exists " << actor_id.Hex();
   }
 
   return inserted;