This post is part of my witness duties to review all code changes made in https://github.com/steemit/steem/.

I was checking the changes since 0.20.5, they can be found here: https://github.com/steemit/steem/compare/v0.20.5...master

Assuring that mana_used is above std::numeric_limits< uint64_t >::min()

That's a useful and necessary change. They assure that used_mana will not jump to an unexpected value when used_mana goes below the numerical minimum.

Resource pool parameters are changed

The budget parameter of all pool is decreased and RC cost raise is prevented by changing a_point_num and a_point_denom.

Removing of the old bandwidth code

The old bandwidth code is removed.

• witness_api_plugin is removed from the condenser_api build instructions
• #include <steem/plugins/witness_api/witness_api_plugin.hpp> is removed from condenser_api.cpp
• get_account_bandwidth is removed
• average_block_size, current_reserve_ratio , max_virtual_bandwidth is removed
• average_bandwidth, lifetime_bandwidth, last_bandwidth_update, average_market_bandwidth, lifetime_market_bandwidth, last_market_bandwidth_update is removed from the account object
• witness_api files from libraries/plugins/apis/witness_api were removed

RC delegation pool objects and operation were added

RC delegation pool objects and operation were added to the current master. This is the first step in implementing RC delegation pools.

• New objects rc_delegation_pool_object_type, rc_indel_edge_object_type, rc_outdel_drc_edge_object_type

New class rc_delegation_pool_object

Represents a delegation pool.
A new class to handle each rc delegation pool was added. Parameter are:

• id_type id;
• account_name_type account;
• steem::chain::util::manabar rc_pool_manabar;

New class rc_indel_edge_object

Represents a delegation from a user to a pool.
Parameter:

• id_type                       id;
  

•  account_name_type             from_account;
  

• account_name_type             to_pool;
  

•  share_type                    amount;
  

New class rc_outdel_drc_edge_object

 * Represents a delegation from a pool to a user based on delegated resource credits (DRC).
 *
 * In the case of a pool that is not under heavy load, DRC:RC has a 1:1 exchange rate.
 *
 * However, if the pool drops below STEEM_RC_DRC_FLOAT_LEVEL, DRC:RC exchange rate starts
 * to rise according to `f(x) = 1/(a+b*x)` where `x` is the pool level, and coefficients `a`,
 * `b` are set such that `f(STEEM_RC_DRC_FLOAT_LEVEL) = 1` and `f(0) = STEEM_RC_MAX_DRC_RATE`.
 *
 * This ensures the limited RC of oversubscribed pools under heavy load are
 * shared "fairly" among their users proportionally to DRC.  This logic
 * provides a smooth transition between the "fiat regime" (i.e. DRC represent
 * a direct allocation of RC) and the "proportional regime" (i.e. DRC represent
 * the fraction of RC that the user is allowed).

Parameter:

•  id_type                       id;
  

•  account_name_type             from_pool;
  

•  account_name_type             to_account;
  

•  steem::chain::util::manabar   drc_manabar;
  

•  int64_t                       drc_max_mana = 0;
  

New container to store the state and operation of the RC pool delegation has been added

New operation delegate_to_pool_operation was added

This operation can be used to delegate RC from an account to a pool.

Operation parameter:

• account_name_type from_account;
• account_name_type to_pool;
• share_type amount;

New operation delegate_drc_from_pool_operation was added

This operation can be used to allow account use RC from a pool. The operation has to be signed from the pool owner.

Operation parameter:

• account_name_type from_pool;
• account_name_type to_account;
• int64_t mana_change = 0;
• int64_t drc_max_mana = 0;

Changes in the RC cost calculation

The most important change is that resource_execution_time are now used for resource_count calculation. This is done by adding the missing

result.resource_count[ resource_execution_time ] += vtor.execution_time_count;

exec_time for custom_json are made a lot cheaper

The calculation time custom_operation_exec_time has been reduced from 228000 to 11400.
Rc costs for a follow remain high:

 exec_time *= EXEC_FOLLOW_CUSTOM_OP_SCALE;

RC costs for a vote is reduced by factor of 19

• comment_vote_object_base_size is changed from 47 *STATE_BYTES_SCALE to 47 *STATE_COMMENT_VOTE_BYTE_SIZE

RC changes - New Maximum negative mana added

• define STEEM_RC_MAX_NEGATIVE_PERCENT 166
• int64_t min_mana = -1 * ( STEEM_RC_MAX_NEGATIVE_PERCENT * mbparams.max_mana ) / STEEM_100_PERCENT;

Code cleanup/improvements

• Some code cleanup/improvements regarding handling of the first block
• Some code cleanup regarding the removed modifier for account creation
• SMT unit test were added

Conclusion

The code changes contain some uncritical code clean up regarding

• old bandwidth system is removed
• handling of the first block
• removed modifier for account creation

The most important change is the adding of objects for resource pool delegations . This is the first necessary step in implementing a fully working pool delegation. New objects, container and operation have been added to implement this feature. It will be possible to use delegate_to_pool_operation for creating a new RC pool. delegate_drc_from_pool_operation can be used to allow other accounts using the pool.

The second most important change is the enabling of resource_execution_time for RC costs. The budget of all pools have been increased to compensate this. The cost of a vote has made 19x cheaper, custom_json operation was also made 20x cheaper (except of follow custom json operation).

Some code improvements were made:

• New maximum negative mana have been defined (166 % of max_mana)
• Check added to assure that mana_used is above a defined minimum value

The changes are looking promising to me.