mathieuprog/retry_on

Elixir utility for retrying Ecto operations

RetryOn

retry_on_stale/2

retry_on_stale/2 performs an operation that might raise an Ecto.StaleEntryError error and retries it a specified number of times with a delay between each attempt.

Example

The example features a wallet's balance_amount, protected by optimistic locking to prevent race conditions. The retry_on_stale/2 function handles Ecto.StaleEntryError from concurrent transactions, refetching the wallet and retrying the operation.

import RetryOn, only: [retry_on_stale: 2]

def increase_wallet_balance(%Wallet{} = wallet, amount) do
  retry_on_stale(
    fn attempt ->
      # refetch the latest wallet data for subsequent attempts
      wallet = if attempt == 1, do: wallet, else: Repo.get!(Wallet, wallet.id)

      # this function could raise a StaleEntryError
      do_increase_wallet_balance(wallet, amount)
    end,
    max_attempts: 5, delay_ms: 100
  )
end

defp do_increase_wallet_balance(%Wallet{} = wallet, amount) do
  new_balance = Decimal.add(wallet.balance_amount, amount)

  wallet
  |> Ecto.Changeset.change(balance_amount: new_balance)
  |> Ecto.Changeset.optimistic_lock(:lock_version)
  |> Repo.update!()
end

Options

:max_attempts - The maximum number of attempts to perform the operation before giving up and re-raising the last Ecto.StaleEntryError.

:delay_ms - The delay in milliseconds between each attempt.

retry_on_unique_constraint/3

retry_on_unique_constraint/3 performs an operation that might raise an Ecto.UniqueConstraintError error and retries it a specified number of times with a delay between each attempt.

Example

import RetryOn, only: [retry_on_unique_constraint: 2]

retry_on_unique_constraint(
  Repo,
  :my_field,
  fn _ ->
    # Code that performs an operation which may result in a unique constraint error on `:my_field`.
    # The function is retried if a unique constraint error is found in a `{:error, changeset}` tuple or
    # an `%Ecto.InvalidChangesetError{changeset: changeset}` error.
  end,
  max_attempts: 2, delay_ms: 500
)

Options

:max_attempts - The maximum number of attempts to perform the operation before giving up and re-raising the last Ecto.StaleEntryError.

:delay_ms - The delay in milliseconds between each attempt.

Installation

Add retry_on for Elixir as a dependency in your mix.exs file:

def deps do
  [
    {:retry_on, "~> 0.1.0"}
  ]
end

HexDocs

HexDocs documentation can be found at https://hexdocs.pm/retry_on.