Module polkadot_runtime_parachains::dmp

To prevent Out of Memory errors on the DownwardMessageQueue, an exponential fee factor (DeliveryFeeFactor) is set. The fee factor increments exponentially after the number of messages in the DownwardMessageQueue passes a threshold. This threshold is set as:

// Maximum max sized messages that can be send to
// the DownwardMessageQueue before it runs out of memory
max_messages = MAX_POSSIBLE_ALLOCATION / max_downward_message_size
threshold = max_messages / THRESHOLD_FACTOR

Based on the THRESHOLD_FACTOR, the threshold is set as a fraction of the total messages. The DeliveryFeeFactor increases for a message over the threshold by:

DeliveryFeeFactor = DeliveryFeeFactor * (EXPONENTIAL_FEE_BASE + MESSAGE_SIZE_FEE_BASE * encoded_message_size_in_KB)

And decreases when the number of messages in the DownwardMessageQueue fall below the threshold by:

DeliveryFeeFactor = DeliveryFeeFactor / EXPONENTIAL_FEE_BASE

As an extra defensive measure, a max_messages hard limit is set to the number of messages in the DownwardMessageQueue. Messages that would increase the number of messages in the queue above this hard limit are dropped.

Re-exports

• pub use pallet::*;

Modules

• pallet
  The pallet module in each FRAME pallet hosts the most important items needed to construct this pallet.

Enums

• QueueDownwardMessageError
  An error sending a downward message.