Transaction Processor

Relevant To: All chains


The transaction processor is the part of the chain which processes queued transactions into blocks and fixates them on the blockchain.

For level 1 chains, this happens on a fixed period every 5 seconds. For chains level 2-4, it is event based and runs whenever there are new transactions with which to make blocks. Level 5 will check every minute, but will only create a block and broadcast to public networks on a specific interval. This is because broadcasting to some public networks can be prohibitively expensive.


In order to run the contract invoker, sh entrypoints/ should be used as the command of the built docker container.


The transaction processor is scheduled via APScheduler to allow the transaction processor to be re-executed on an interval. However, if a block is currently being processed, a new block will not start processing. This is because chains must have the previous block hash in order to create the next block (hence ‘blockchain’).

The transaction processor uses the queue from which manages state with redis for what will be included in an upcoming block. This is equivalent to a ‘mempool’ on other blockchains. This state is managed under the redis keys dc:tx:incoming for unprocessed items, and dc:tx:processing for items that are currently being processed (and can be recovered and re-processed in the case of an error/crash).


The general loop of the transaction processor goes as follows:

  • Check and renew Dragon Net registration if necessary

  • Retrieve all items from the queue (transactions on L1 chains, or blocks for verification level (2-5) nodes)

  • A block is created by placing items into block. If it is a verification node, then verification occurs here

  • The block is signed and stored. For L1 chains, it is added to the broadcast queue. For verification nodes, the block is sent to the requesting L1 chain(s) as receipt

  • The items are cleared off the queue and the process exits

For L5 nodes, this is slightly altered. Where normally a block would be created immediately, L5s store transactions until their BROADCAST_INTERVAL has expired, then creates a block containing the all transactions since the last broadcast. This block’s hash is then broadcast to a public network.

After broadcasting to a public network, L5 nodes will wait until the transaction has been confirmed before sending the receipt to L1 chains whose blocks are contained within the L5 block.