P5-commentary.txt

                      Protocol update commentary

Protocol Version: 5
Builds on Protocol Version: 4

Protocol version 5 adds support for upgradable smart contracts and
allows smart contracts to query additional data from the chain. The
protocol update also allows smart contracts to use more resources and
introduces a major reorganization of the account storage. The
reorganization allows for more efficient account retrieval and updates.

The key user-visible features are related to smart contracts.

1. Smart contract writers can now make their smart contracts upgradable.
   This is an opt-in ability and allows the writer of the contract to
   update it to fix any bugs, or introduce additional functionality.
   This feature does not increase the expressive power of smart
   contracts; the same upgradability was already possible via a proxy
   pattern. However it makes writing and testing upgradable smart
   contracts much simpler.
2. A number of resource limitations related to smart contracts have been
   relaxed. The three key ones are:
   - The limit on parameter size for init functions and smart contract
     entrypoints. The limit is now `65535B`, compared to the previous
     limit of `1024B`. A concrete instance where this can be useful is
     in a CIS2 contract when minting, e.g., NFTs. With the increased
     limit more NFTs can be minted in a single transaction.
   - The return value from a V1 smart contract is now unbounded, apart
     from limits imposed by NRG. This allows, for example, view
     functions to return more data, which can be especially useful with
     the node's invoke endpoint for off-chain integration.
   - There is no more hard limit on the number of logs a smart contract
     can emit. This can also be helpful in CIS2 contracts, where, for
     example, each transfer must be logged. The previous limit of 64 log
     items meant that if more than 64 transfers were attempted in the
     same transaction some workarounds were needed.

Other improvements in this protocol update are node internal aimed at
improving node performance and maintainability.

Existing successful contract executions will retain their behaviour.
However if a contract has failed due to hitting one of the resource
limitations in protocol version 4, it may succeed, or fail in a
different way, in protocol version 5.