Nodeos Replays

Nodeos provides various options for replaying blockchain blocks. This can be useful if, for example, a node has downloaded a blocks.log file from the internet (as a faster alternative to synchronizing from the p2p network) and the node wants to use it to quickly catch up with the network, or if you want to know the chain state at specified points in a blockchain's life.

Replaying data can be done in two ways:

• From a blocks.log file:
  The blocks.log file contains all irreversible transactions on the blockchain. All instances of nodeos write irreversible blocks to the blocks.log file, which is located at the data/blocks directory relative to the nodeos directory. Using a blocks.log file to replay will allow you to start a nodeos instance, which recreates the entire history of the blockchain locally, without adding unnecessary load to the network.

• From a snapshot file:
  Snapshot files can be created from a running nodeos instance. The snapshot contains the chain state for the block referenced when created. It is recommended to use snapshot files created from blocks that are irreversible. Using a snapshot file to replay allows you to quickly start a nodeos instance which has a full and correct chain state at a specified block number, but not a full history of transactions up to that block number. From that point on the nodeos instance will operate in the configured manner.

Replay How-Tos

• How To Generate a Blocks Log
• How To Generate a Snapshot
• How To Replay from a Blocks Log
• How to Replay from a Snapshot

Replay Snapshot-specific Options

Typing nodeos --help on the command line will show you all the options available for running nodeos. The snapshot and replay specific options are:

• --force-all-checks
  The node operator may not trust the source of the blocks.log file and may want to run nodeos with --replay-blockchain --force-all-checks the first time to make sure the blocks are good. The --force-all-checks flag can be passed into nodeos to tell it to not skip any checks during replay.

• --disable-replay-opts
  By default, during replay, nodeos does not create a stack of chain state deltas (this stack is used to enable rollback of state for reversible blocks.) This is a replay performance optimization. Using this option turns off this replay optimization and creates a stack of chain state deltas. If you are using the state history plugin you must use this option.

• --replay-blockchain
  This option tells nodeos to replay from the blocks.log file located in the data/blocks directory. nodeos will clear the chain state and replay all blocks.

• --hard-replay-blockchain
  This option tells nodeos to replay from the blocks.log file located in the data/blocks directory. nodeos makes a backup of the existing blocks.log file and will then clear the chain state and replay all blocks. This option assumes that the backup blocks.log file may contain corrupted blocks, so nodeos replays as many blocks as possible from the backup block log. When nodeos finds the first corrupted block while replying from nodeos.log it will synchronize the rest of the blockchain from the p2p network.

• --delete-all-blocks
  This tells nodeos to clear the local chain state and local the blocks.log file, If you intend to then synchronize from the p2p network you would need to provide a correct genesis.json file. This option is not recommended.

• --truncate-at-block
  Default argument (=0), only used if the given value is non-zero. Using this option when replaying the blockchain will force the replay to stop at the specified block number. This option will only work if replaying with the --hard-replay-blockchain option. The local nodeos process will contain the chain state for that block. This option may be useful for checking blockchain state at specific points in time. It is intended for testing/validation and is not intended to be used when creating a local nodeos instance which is synchronized with the network.

• --snapshot
  Use this option to specify which snapshot file to use to recreate the chain state from a snapshot file. This option will not replay the blocks.log file. The nodeos instance will not know the full transaction history of the blockchain.

• --snapshots-dir
  You can use this to specify the location of the snapshot file directory (absolute path or relative to application data dir.)

• --blocks-dir
  You can use this to specify the location of the blocks.log file directory (absolute path or relative to application data dir)