Module slot_based 

Architecture Overview

The block building mechanism operates through two coordinated tasks:

1. Block Builder Task: Orchestrates the timing and execution of parachain block production
2. Collator Task: Processes built blocks into collations for relay chain submission

Block Builder Task Details

The block builder task manages block production timing and execution through an iterative process:

1. Awaits the next production signal from the internal timer
2. Retrieves the current best relay chain block and identifies a valid parent block (see [find_parent_for_building][cumulus_client_consensus_common::find_parent_for_building] for parent selection criteria)
3. Validates that:
   • The parachain has an assigned core on the relay chain
   • No block has been previously built on the target core
4. Executes block building and import operations
5. Transmits the completed block to the collator task

Block Production Timing

When a block is produced is determined by the following parameters:

• Parachain slot duration
• Number of assigned parachain cores
• The target_block_rate runtime API, which determines how many blocks to produce per relay chain slot. When this API is unavailable, the block builder falls back to one block per core. When the target exceeds the number of cores, multiple blocks are bundled per core.

Timing Examples

The following table demonstrates various timing configurations and their effects. The “AURA Slot” column shows which author is responsible for the block.

Slot Duration (ms)	Cores	Production Attempts (ms)	AURA Slot
2000	3	0, 2000, 4000, 6000	0, 1, 2, 3
6000	1	0, 6000, 12000, 18000	0, 1, 2, 3
6000	3	0, 2000, 4000, 6000	0, 0, 0, 1
12000	1	0, 6000, 12000, 18000	0, 0, 1, 1
12000	3	0, 2000, 4000, 6000	0, 0, 0, 0

Collator Task Details

The collator task receives built blocks from the block builder task and performs two primary functions:

1. Block compression
2. Submission to the collation-generation subsystem

Structs

Params

Parameters for run.

SlotBasedBlockImport

Special block import for the slot based collator.

SlotBasedBlockImportHandle

Handle for receiving the block and the storage proof from the SlotBasedBlockImport.

Functions

run

Run aura-based block building and collation task.