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Node Protocol Database Release Date Release Notes GitHub Links
20.0 17 15 2019-11-12 V20.0 Release - Milestone - Changelog
Known Issue V19+: 'Too many open files'
  • Issue: The following error, or a similar one, can be seen when attempting to run a full node on some versions of macOS, Linux and possibly other operating systems. This is most common when using the built-in Qt wallet or other GUI-based wallets: "Exception while running wallet: open: Too many open files" or other errors containing "Too many open files". This is due to some systems having a very low default file descriptor limit and V19.0+ uses more of them after the move to TCP.

  • Solution: Increasing the file limits is needed to resolve this. See this known issue for more details on resolution.

Known Issue V20: Peers stake reporting inaccurate (Windows only)
  • Issue: For Windows builds only, when calling confirmation_quorum RPC the peers_stake_total amount returned may be inaccurate, returning a range from the correct full peer stake amount down to 0.

  • Solution: A solution to the issue has been found and as this is a reporting issue only, the fix will be included in the next released version. For those manually building the node, patching the fix pull request onto the V20.0 tag can resolve the issue now. Or alternatively, building on the V20.0 tag with RelWithDebInfo option, see Build Instructions for Windows.

Upgrade Notices

Only node V18.0 and higher supported

With V20.0 only nodes V18.0 and higher will be peered with on the network (see Active Releases above). This means any nodes running versions earlier than 18.0 will begin to lose peers and fall out of sync over time once upgrades to V20.0 begin.

If you are running a node version earlier than V18.0, please update as soon as possible to avoid disruption.

Database upgrades

Upgrade requires downtime, read carefully

Please review the following details carefully as the automatic database upgrade process will cause downtime for the node.

This version brings some new optimizations to the ledger which require database upgrades to be performed. Due to the nature of upgrades, the following impacts will occur:

  • Upgrade times depend on specs of the node host but are expected to be between 5 and 15 minutes for most cases.
  • Upgrade activities are synchronous which means the node will not be participating on the network and RPC requests won’t be available during the upgrade process - services requiring uptime should plan to swap out their ledger for one upgraded by a separate node or download from a trusted source.
  • Ledger size will grow by up to 50% during this process - please ensure you have free disk space of 3x the current ledger before starting the upgrade (currently ~16GB on the main network).
  • A database vacuum will be automatically performed after the upgrade to reclaim disk space, which can be verified complete in the logs.
  • Doing proper ledger backups is recommended before starting this process. Ensure you have enough disk space to allow for any ledger backups plus the additional disk space required for the database upgrade mentioned above. A new config option in V20, node.backup_before_upgrade, will allow for automated ledger backups between future versions.

New .toml config files

A new setup in V20.0 uses internal default config values, so config files are only needed for non-default settings. During upgrade new .toml format files will be created for the config.json and rpc_config.json files if they contain non-default values. Before migration config_backup_toml_migration.json and rpc_config_backup_toml_migration.json files will be created for backup.

The following commands can be used to generated commented out, complete config files for review:

Only set non-default values in .toml files

It is not recommended to uncomment all values in the .toml file output from commands below. Instead, only uncomment or insert non-default values to ensure any default value changes in future release are only overridden when needed.

Name Description Generated with
config-node.toml Node configuration nano_node --generate_config node
config-rpc.toml RPC configuration nano_node --generate_config rpc
config-nano-pow-server.toml Proof of work server configuration nano_pow_server --generate_config
config-qtwallet.toml Qt developer wallet configuration This file is maintained by the Qt wallet

More details on the new configuration setup can be found in the node Configuration documentation.

Networking changes

Improvements to default network setup in this version requires less setup from node operators, specifically around port forwarding. Although new setups will immediately benefit, any existing systems that have already setup port forwarding may be impacted by these changes. For those systems, we recommend validating your network setup allows proper peering with a test V20.0 node prior to upgrading. If you run into issues, review the Troubleshooting UPnP documentation for assistance. Additional help can be sought in the Node and Representative Management forum category.

Proof-of-Work management

A couple changes to PoW management that services should be aware of:

  • With OpenCL enabled, nodes will still use the local CPU for work generation by default. Setting node.work_threads to 0 will turn this off if required.
  • Regenerating PoW for delayed transactions during high network load will now happen by default through the process RPC. If you wish to turn this off, setting watch_work to false is required.

Other updates to review
Improvements to the External Management and Block Confirmation and Tracking documentation should help clarify the recommended approaches to building integrations.

Major Updates

Migration to .toml config files

Better legibility, support for comments, and no more having the node write to your config files are some of the benefits of this upgrade. Any non-default values captured in your existing .json files will be migrated and you can export a full list of configuration options for use with simple commands. See additional callouts in Upgrade Notices above and in the node Configuration documentation.

Proof-of-Work regeneration outside development wallet

Any requests to the process RPC will have the new watch_work option turned on by default, allowing the node to regenerate Proof-of-Work for blocks even if they are outside of the node’s development wallet. This makes Dynamic PoW and prioritization function more consistently across the network. If you have an external integration utilizing this RPC call, you will automatically start taking advantage of rework during confirmation delays on the network.

RocksDB experimental support

With better disk IO usage, RocksDB is being introduced in this version with experimental support. It is not recommended for use in production, but those interested in testing out a more performant database for the ledger should checkout how to install RocksDB and try it out on development and test systems. We also have a related discussion in our forum for those interested.

Active elections and other optimizations

Thanks to our excellent community testers putting effort into collecting and analyzing block, voting and confirmation data from the beta network, we’ve found various optimizations with the active elections process, confirmation request attempts and bootstrapping behaviors. Various changes have been implemented to help reduce resource usage on nodes in various areas and increase the available throughput on the network. This feature also enhances the effectiveness of prioritization and rework of PoW. No action is needed to take advantage of these great updates.

Infrastructure for PoW transition

Back in September we announced a new PoW algorithm design we had been working on which aimed to be memory hard. After open sourcing an implementation of the algorithm, an efficient low-memory solution was found and we subsequently removed the algorithm implementation from V20.

As part of the original implementation work we were able to setup infrastructure for moving PoW out of the node process in the future, and also added support for version 2 of epoch blocks, which will allow the network upgrade later when a new PoW algorithm is ready. These updates will be included in Lydia but not be utilized until a future version. To follow along with node releases going forward, check out the Upcoming Features page.

RPC Updates

  • BEHAVIOR CHANGE process now takes an optional flag watch_work (default true). Unless set to false, processed blocks can be subject to PoW rework
  • BEHAVIOR CHANGE bootstrap, bootstrap_any and boostrap_lazy will now throw errors when certain launch flags are used to disabled bootstrap methods - see each RPC page for details
  • BEHAVIOR CHANGE RPCs requiring work generation will now throw errors when work generation is disabled (no work peers, no OpenCL and no work threads configured)
  • block_count no longer requires config option enable_control to get the cemented block count
  • unchecked now takes an optional flag json_block to return blocks in JSON-format
  • version now includes more fields - network label, identifier (hash of the genesis open block) and build information
  • peers and node_id now return node IDs with a node_ prefix
  • work_generate and work_validate can now take a multiplier (against base difficulty) to set a different difficulty threshold

CLI Updates

  • NEW generate_config [node|rpc] prints sample configuration files to stdout
    • use_defaults additional argument to generate uncommented entries (not recommended)
  • NEW config passes configuration arguments, alternative to setting in the config file

Node Configuration Updates

Support in Nano Forum

For node operators looking to upgrade to V20.0 or tune their configurations, the Node and Representative Management category of the forum is a great resource to use.

Generate .toml config to see options

As noted in the Upgrade Notices above, this version will migrate your existing .json files over to .toml files. Only non-default values for these fields will be added to the new .toml file. If you wish to adjust other options, use the config generation commands to see all available options.

The following options are notable node configuration updates. Additional configuration changes have been included in this release and can be found when generating the config files.

  • backup_before_upgrade (default false) enables automatic backup of the ledger and wallet databases when updating to a new node version
  • work_watcher_period (default 5 seconds) controls how frequently the node should check the confirmation status of block in the work watcher, and re-generate higher difficulty work if unconfirmed
  • max_work_generate_multiplier (default 64.0) previously max_work_generate_difficulty, now a multiplier for easier management, specifies the absolute maximum difficulty multiplier to be used for work generation

Developer/Debug Options

  • New RPC epoch_upgrade allowing easier epoch distribution (Note - this epoch requires a special private key to be used, see the Network Upgrades page for information)
  • RPC bootstrap has a new optional "bypass_frontier_confirmation"
  • RPC bootstrap_status now displays more data about the current bootstrap attempt
  • New CLI debug_stacktrace displays an example stacktrace, simulating an unexpected program crash
  • New CLI debug_account_versions displays the total number of accounts separated by version and opened/unopened
  • CLI debug_validate_blocks updated to cover more cases
  • CLI debug_profile_verify renamed to debug_profile_validate and now provides simplified work validation profiling
  • New CMake build options:
  • NANO_ROCKSDB enables use of the RocksDB database backend, experimental
  • NANO_WARN_TO_ERR turns compiler warnings into errors on Linux/Mac
  • NANO_TIMED_LOCKS provides information on mutexes held for a long time
  • NANO_STACKTRACE_BACKTRACE uses libbacktrace to provide stacktraces
  • CI_BUILD if set, uses the TRAVIS_TAG environment variable to modify the locally reported node version, to help with support tickets


The following functionality is now deprecated and will be removed in a future release:

  • Addresses containing a dash (ex. nano- or xrb-) are being deprecated and will not longer be compatible with the node in a future release. Addresses using underscores will only be supported.