Crate pallet_bags_list

source ·
Expand description

Bags-List Pallet

A semi-sorted list, where items hold an AccountId based on some Score. The AccountId (id for short) might be synonym to a voter or nominator in some context, and Score signifies the chance of each id being included in the final SortedListProvider::iter.

It implements frame_election_provider_support::SortedListProvider to provide a semi-sorted list of accounts to another pallet. It needs some other pallet to give it some information about the weights of accounts via frame_election_provider_support::ScoreProvider.

This pallet is not configurable at genesis. Whoever uses it should call appropriate functions of the SortedListProvider (e.g. on_insert, or unsafe_regenerate) at their genesis.

Goals

The data structure exposed by this pallet aims to be optimized for:

  • insertions and removals.
  • iteration over the top* N items by score, where the precise ordering of items doesn’t particularly matter.

Details

  • items are kept in bags, which are delineated by their range of score (See Config::BagThresholds).
  • for iteration, bags are chained together from highest to lowest and elements within the bag are iterated from head to tail.
  • items within a bag are iterated in order of insertion. Thus removing an item and re-inserting it will worsen its position in list iteration; this reduces incentives for some types of spam that involve consistently removing and inserting for better position. Further, ordering granularity is thus dictated by range between each bag threshold.
  • if an item’s score changes to a value no longer within the range of its current bag the item’s position will need to be updated by an external actor with rebag (update), or removal and insertion.

Re-exports

Modules

  • migrations
    The migrations of this pallet.
  • pallet
    The module that hosts all the FRAME types needed to add this pallet to a runtime.
  • weights
    Autogenerated weights for pallet_bags_list

Macros

Structs

  • Bag
    A Bag is a doubly-linked list of ids, where each id is mapped to a Node.
  • List
    The ONLY entry point of this module. All operations to the bags-list should happen through this interface. It is forbidden to access other module members directly.
  • Node
    A Node is the fundamental element comprising the doubly-linked list described by Bag.

Enums

Functions