package tezos-protocol-alpha

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package tezos-protocol-alpha
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This module implements a mempool structure meant to be used by a shell and bakers in order to incrementally accumulate commutative operations which could then be safely used to bake a new block. These mempool components guarantee a set of properties useful for these purposes:

  • Every operation contained in a mempool is valid;
  • All the mempool's operations can safely be included (and applicable) in a block in an arbitrary order which means operations commutes. However, to build a valid block with these operations:
  • Operations must be reorganized with regards to their validation passes.
  • Block's operations quota are ignored, it is the baker's responsability to ensure that the set of selected operations does not exceed gas/size operations quota.
  • The baker must also include the required preendorsements and endorsements.
  • The merging of two mempools also maintains the aforementioned properties.

Mempools do not depend on local data and therefore are serializable. This is useful when a node needs to send a mempool to another (remote-)process (e.g. the baker).

type t

Mempool type

type validation_info

Validation info type required to validate and add operations to a mempool.

Type of the function that may be provided in order to resolve a potential conflict when adding an operation to an existing mempool or when merging two mempools. This handler may be defined as a simple order relation over operations (e.g. prioritize the most profitable operations) or an arbitrary one (e.g. prioritize operations where the source is a specific manager).

Returning `Keep will leave the mempool unchanged and retain the existing_operation while returning `Replace will remove existing_operation and add new_operation instead.

type add_result =
  1. | Added
    (*

    Added means that an operation was successfully added to the mempool without any conflict.

    *)
  2. | Replaced of {
    1. removed : Tezos_protocol_environment_alpha.Operation_hash.t;
    }
    (*

    Replaced {removed} means that an operation was successfully added but there was a conflict with the removed operation which was removed from the mempool.

    *)
  3. | Unchanged
    (*

    Unchanged means that there was a conflict with an existing operation which was considered better by the conflict_handler, therefore the new operation is discarded and the mempool remains unchanged.

    *)

Return type when adding an operation to the mempool

type add_error =
  1. | Validation_error of Tezos_protocol_environment_alpha.Error_monad.error Tezos_protocol_environment_alpha.Error_monad.trace
    (*

    Validation_error _ means that the operation is invalid.

    *)
  2. | Add_conflict of operation_conflict
    (*

    Add_conflict _ means that an operation conflicts with an existing one. This error will only be obtained when no conflict_handler was provided. Moreover, Validation_error _ takes precedence over Add_conflict _ which implies that we have the implicit invariant that the operation would be valid if there was no conflict. Therefore, if add_operation would have to be called again, it would be redondant to check the operation's signature.

    *)

Error type returned when adding an operation to the mempool fails.

type merge_error =
  1. | Incompatible_mempool
    (*

    Incompatible_mempool _ means that the two mempools are not built ontop of the same head and therefore cannot be considered.

    *)
  2. | Merge_conflict of operation_conflict
    (*

    Merge_conflict _ arises when two mempools contain conflicting operations and no conflict_handler was provided.

    *)

Error type returned when the merge of two mempools fails.

Mempool encoding

Initialize a static validation_info and mempool, required to validate and add operations, and an incremental and serializable mempool.

Adds an operation to a mempool if and only if it is valid and does not conflict with previously added operations.

This function checks the validity of an operation (see Validate.check_operation) and tries to add it to the mempool.

If an error occurs during the validation, the result will be a Validation_error <err>. If a conflict with a previous operation exists, the result will be an Add_conflict (see Validate.check_operation_conflict). Important: no Add_conflict will be raised if a conflict_handler is provided (see add_result).

If no error is raised the operation is potentially added to the mempool depending on the add_result value.

remove_operation mempool oph removes the operation oph from the mempool. The mempool remains unchanged when oph is not present in the mempool

merge ?conflict_handler existing_mempool new_mempool merges new_mempool into existing_mempool.

Mempools may only be merged if they are compatible: i.e. both have been initialised with the same predecessor block. Otherwise, the Incompatible_mempool error is returned.

Conflicts between operations from the two mempools can occur. Similarly as add_operation, a Merge_conflict error may be raised when no conflict_handler is provided.

existing_operation in conflict_handler ~existing_operation ~new_operation references operations present in existing_mempool while new_operation will reference operations present in new_mempool.

operations mempool returns the map of operations present in mempool.

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