View Source DBConnection.Ownership (db_connection v2.4.3)

A DBConnection pool that requires explicit checkout and checkin as a mechanism to coordinate between processes.

options

Options

  • :ownership_mode - When mode is :manual, all connections must be explicitly checked out before by using ownership_checkout/2. Otherwise, mode is :auto and connections are checked out implicitly. {:shared, owner} mode is also supported so processes are allowed on demand. On all cases, checkins are explicit via ownership_checkin/2. Defaults to :auto.
  • :ownership_timeout - The maximum time that a process is allowed to own a connection, default 120_000. This timeout exists mostly for sanity checking purposes and can be increased at will, since DBConnection automatically checks in connections whenever there is a mode change.
  • :ownership_log - The Logger.level to log ownership changes, or nil not to log, default nil.

There are also two experimental options, :post_checkout and :pre_checkin which allows a developer to configure what happens when a connection is checked out and checked in. Those options are meant to be used during tests, and have the following behaviour:

  • :post_checkout - it must be an anonymous function that receives the connection module, the connection state and it must return either {:ok, connection_module, connection_state} or {:disconnect, err, connection_module, connection_state}. This allows the developer to change the connection module on post checkout. However, in case of disconnects, the return connection_module must be the same as the connection_module given. Defaults to simply returning the given connection module and state.

  • :pre_checkin - it must be an anonymous function that receives the checkin reason (:checkin, {:disconnect, err} or {:stop, err}), the connection module and the connection state returned by post_checkout. It must return either {:ok, connection_module, connection_state} or {:disconnect, err, connection_module, connection_state} where the connection module is the module given to :post_checkout Defaults to simply returning the given connection module and state.

callers-lookup

Callers lookup

When checking out, the ownership pool first looks if there is a connection assigned to the current process and then checks if there is a connection assigned to any of the processes listed under the $callers process dictionary entry. The $callers entry is set by default for tasks from Elixir v1.8.

You can also pass the :caller option on checkout with a pid and that pid will be looked up first, instead of self(), and then we fall back to $callers.

Link to this section Summary

Functions

Allows the process given by allow to use the connection checked out by owner_or_allowed.

Checks a connection back in.

Explicitly checks a connection out from the ownership manager.

Changes the ownership mode.

Link to this section Functions

Link to this function

ownership_allow(manager, owner, allow, opts)

View Source
@spec ownership_allow(
  GenServer.server(),
  owner_or_allowed :: pid(),
  allow :: pid(),
  Keyword.t()
) ::
  :ok | {:already, :owner | :allowed} | :not_found

Allows the process given by allow to use the connection checked out by owner_or_allowed.

It may return :ok if the connection is checked out. {:already, :owner | :allowed} if the allow process already has a connection. owner_or_allowed may either be the owner or any other allowed process. Returns :not_found if the given process does not have any connection checked out.

Link to this function

ownership_checkin(manager, opts)

View Source
@spec ownership_checkin(GenServer.server(), Keyword.t()) ::
  :ok | :not_owner | :not_found

Checks a connection back in.

A connection can only be checked back in by its owner.

Link to this function

ownership_checkout(manager, opts)

View Source
@spec ownership_checkout(GenServer.server(), Keyword.t()) ::
  :ok | {:already, :owner | :allowed}

Explicitly checks a connection out from the ownership manager.

It may return :ok if the connection is checked out. {:already, :owner | :allowed} if the caller process already has a connection, :error if it could be not checked out or raise if there was an error.

Link to this function

ownership_mode(manager, mode, opts)

View Source
@spec ownership_mode(
  GenServer.server(),
  :auto | :manual | {:shared, pid()},
  Keyword.t()
) ::
  :ok | :already_shared | :not_owner | :not_found

Changes the ownership mode.

mode may be :auto, :manual or {:shared, owner}.

The operation will always succeed when setting the mode to :auto or :manual. It may fail with reason :not_owner or :not_found when setting {:shared, pid} and the given pid does not own any connection. May return :already_shared if another process set the ownership mode to {:shared, _} and is still alive.