DefaultCatchUpThreshold is the number of blocks that if the execution is far behind the finalization then we will only lazy load the next unexecuted finalized blocks until the execution has caught up.

MaxConcurrentBlockExecutor is the maximum number of concurrent block executors.

MaxProcessableBlocks is the maximum number of blocks that is queued to be processed.

BlockIDHeight is a helper struct that holds the block ID and height.

BlockThrottle is a helper struct that helps throttle the unexecuted blocks to be sent to the block queue for execution.

Core connects the execution components when it receives blocks and collections, it forwards them to the block queue.

An Engine receives and saves incoming blocks.

Machine forwards blocks and collections to the core for processing.

CollectionFetcher abstracts the details of how to fetch collection.

Throttle is used to throttle the blocks to be added to the processables channel.