Resolve #97: Add exponentially growing fees on account creation

It scales up aggressively right now; this can be adjusted later. I just
wanted to demonstrate that it works.

libraries/chain/account_evaluator.cpp

@@ -108,6 +108,17 @@ object_id_type account_create_evaluator::do_apply( const account_create_operatio
          obj.options.memo_key = get_relative_id(obj.options.memo_key);
    });
 
+   const auto& global_properties = db().get_global_properties();
+   const auto& dynamic_properties = db().get_dynamic_global_properties();
+   db().modify(dynamic_properties, [](dynamic_global_property_object& p) {
+      ++p.accounts_registered_this_interval;
+   });
+   if( dynamic_properties.accounts_registered_this_interval %
+       global_properties.parameters.accounts_per_fee_scale == 0 )
+      db().modify(global_properties, [&dynamic_properties](global_property_object& p) {
+         p.parameters.current_fees.account_create_fee <<= p.parameters.account_fee_scale_bitshifts;
+      });
+
    return new_acnt_object.id;
 } FC_CAPTURE_AND_RETHROW((o)) }
 

libraries/chain/db_maint.cpp

@@ -429,11 +429,18 @@ void database::perform_chain_maintenance(const signed_block& next_block, const g
    update_active_witnesses();
    update_active_delegates();
 
-   if( gpo.pending_parameters )
+   modify(gpo, [this](global_property_object& p) {
-      modify(gpo, [](global_property_object& p) {
+      // Remove scaling of account registration fee
+      const auto& dgpo = get_dynamic_global_properties();
+      p.parameters.current_fees.account_create_fee >>= p.parameters.account_fee_scale_bitshifts *
+            (dgpo.accounts_registered_this_interval / p.parameters.accounts_per_fee_scale);
+
+      if( p.pending_parameters )
+      {
          p.parameters = std::move(*p.pending_parameters);
          p.pending_parameters.reset();
-      });
+      }
+   });
 
    auto new_block_interval = global_props.parameters.block_interval;
 
@@ -445,7 +452,7 @@ void database::perform_chain_maintenance(const signed_block& next_block, const g
    if( !r )
    {
       _pending_block.timestamp -=  r;
-      assert( (_pending_block.timestamp.sec_since_epoch() % new_block_interval)  == 0 );
+      assert( (_pending_block.timestamp.sec_since_epoch() % new_block_interval) == 0 );
    }
 
    auto next_maintenance_time = get<dynamic_global_property_object>(dynamic_global_property_id_type()).next_maintenance_time;
@@ -465,6 +472,7 @@ void database::perform_chain_maintenance(const signed_block& next_block, const g
 
    modify(get_dynamic_global_properties(), [next_maintenance_time](dynamic_global_property_object& d) {
       d.next_maintenance_time = next_maintenance_time;
+      d.accounts_registered_this_interval = 0;
    });
 
    // Reset all BitAsset force settlement volumes to zero

libraries/chain/include/graphene/chain/config.hpp

@@ -93,6 +93,8 @@
 #define GRAPHENE_WITNESS_PAY_PERCENT_PRECISION                (1000000000)
 #define GRAPHENE_DEFAULT_MAX_ASSERT_OPCODE                    1
 #define GRAPHENE_DEFAULT_FEE_LIQUIDATION_THRESHOLD            GRAPHENE_BLOCKCHAIN_PRECISION * 100;
+#define GRAPHENE_DEFAULT_ACCOUNTS_PER_FEE_SCALE               1000
+#define GRAPHENE_DEFAULT_ACCOUNT_FEE_SCALE_BITSHIFTS          4
 #define GRAPHENE_GENESIS_TIMESTAMP                            (1431700000)  /// Should be divisible by GRAPHENE_DEFAULT_BLOCK_INTERVAL
 
 #define GRAPHENE_MAX_WORKER_NAME_LENGTH                       63

libraries/chain/include/graphene/chain/global_property_object.hpp

@@ -76,10 +76,10 @@ namespace graphene { namespace chain {
          time_point_sec    next_maintenance_time;
          time_point_sec    last_budget_time;
          share_type        witness_budget;
+         uint32_t          accounts_registered_this_interval;
    };
 }}
 
-
 FC_REFLECT_DERIVED( graphene::chain::dynamic_global_property_object, (graphene::db::object),
                     (random)
                     (head_block_number)
@@ -88,6 +88,7 @@ FC_REFLECT_DERIVED( graphene::chain::dynamic_global_property_object, (graphene::
                     (current_witness)
                     (next_maintenance_time)
                     (witness_budget)
+                    (accounts_registered_this_interval)
                   )
 
 FC_REFLECT_DERIVED( graphene::chain::global_property_object, (graphene::db::object),

libraries/chain/include/graphene/chain/types.hpp

@@ -345,7 +345,7 @@ namespace graphene { namespace chain {
       }
 
       uint32_t key_create_fee = 270300; ///< the cost to register a public key with the blockchain
-      uint32_t account_create_fee = 666666; ///< the cost to register the cheapest non-free account
+      uint64_t account_create_fee = 666666; ///< the cost to register the cheapest non-free account
       uint32_t account_update_fee = 150000; ///< the cost to update an existing account
       uint32_t account_transfer_fee = 300000; ///< the cost to transfer an account to a new owner
       uint32_t account_whitelist_fee = 300000; ///< the fee to whitelist an account
@@ -457,6 +457,8 @@ namespace graphene { namespace chain {
       share_type              worker_budget_per_day               = GRAPHENE_DEFAULT_WORKER_BUDGET_PER_DAY; ///< CORE to be allocated to workers (per day)
       uint16_t                max_predicate_opcode                = GRAPHENE_DEFAULT_MAX_ASSERT_OPCODE; ///< predicate_opcode must be less than this number
       share_type              fee_liquidation_threshold           = GRAPHENE_DEFAULT_FEE_LIQUIDATION_THRESHOLD; ///< value in CORE at which accumulated fees in blockchain-issued market assets should be liquidated
+      uint16_t                accounts_per_fee_scale              = GRAPHENE_DEFAULT_ACCOUNTS_PER_FEE_SCALE; ///< number of accounts between fee scalings
+      uint8_t                 account_fee_scale_bitshifts         = GRAPHENE_DEFAULT_ACCOUNT_FEE_SCALE_BITSHIFTS; ///< number of times to left bitshift account registration fee at each scaling
 
       void validate()const
       {
@@ -616,6 +618,8 @@ FC_REFLECT( graphene::chain::chain_parameters,
             (worker_budget_per_day)
             (max_predicate_opcode)
             (fee_liquidation_threshold)
+            (accounts_per_fee_scale)
+            (account_fee_scale_bitshifts)
           )
 
 FC_REFLECT_TYPENAME( graphene::chain::share_type )

tests/tests/block_tests.cpp

@@ -839,4 +839,27 @@ BOOST_FIXTURE_TEST_CASE( witness_scheduler_missed_blocks, database_fixture )
    });
 } FC_LOG_AND_RETHROW() }
 
+BOOST_FIXTURE_TEST_CASE( account_create_fee_scaling, database_fixture )
+{ try {
+   auto accounts_per_scale = db.get_global_properties().parameters.accounts_per_fee_scale;
+   enable_fees(1);
+
+   BOOST_CHECK_EQUAL(db.get_global_properties().parameters.current_fees.account_create_fee, 1);
+   for( int i = db.get_dynamic_global_properties().accounts_registered_this_interval; i < accounts_per_scale; ++i )
+      create_account("shill" + fc::to_string(i));
+   generate_block();
+   BOOST_CHECK_EQUAL(db.get_global_properties().parameters.current_fees.account_create_fee, 16);
+   for( int i = 0; i < accounts_per_scale; ++i )
+      create_account("moreshills" + fc::to_string(i));
+   generate_block();
+   BOOST_CHECK_EQUAL(db.get_global_properties().parameters.current_fees.account_create_fee, 256);
+   for( int i = 0; i < accounts_per_scale; ++i )
+      create_account("moarshills" + fc::to_string(i));
+   generate_block();
+   BOOST_CHECK_EQUAL(db.get_global_properties().parameters.current_fees.account_create_fee, 4096);
+
+   generate_blocks(db.get_dynamic_global_properties().next_maintenance_time);
+   BOOST_CHECK_EQUAL(db.get_global_properties().parameters.current_fees.account_create_fee, 1);
+} FC_LOG_AND_RETHROW() }
+
 BOOST_AUTO_TEST_SUITE_END()