Ecto - Upgrading to 3.0

set adapter in MyApp.Repo module

retrieving adapter from config files is deprecated.


# lib/my_app/repo.ex

defmodule MyApp.Repo do
  use Ecto.Repo,
    otp_app: :my_app,
    adapter: Ecto.Adapters.Postgres

increase connection pool size to at least 2

if pool_size is set to 1, Ecto.MigrationError will be raised when trying to run pending migrations:


def lock_for_migrations(meta, query, opts, fun) do
 %{opts: default_opts} = meta

  if Keyword.fetch(default_opts, :pool_size) == {:ok, 1} do

  # ...

defp raise_pool_size_error do
  raise Ecto.MigrationError, """
  Migrations failed to run because the connection pool size is less than 2.
  Ecto requires a pool size of at least 2 to support concurrent migrators.
  When migrations run, Ecto uses one connection to maintain a lock and
  another to run migrations.
  If you are running migrations with Mix, you can increase the number
  of connections via the pool size option:
      mix ecto.migrate --pool-size 2
  If you are running the Ecto.Migrator programmatically, you can configure
  the pool size via your application config:
      config :my_app, Repo,
        pool_size: 2 # at least


make sure pool_size is at least 2 in all environments.

use telemetry events instead of loggers

[Ecto.Repo] The :loggers configuration is deprecated in favor of “Telemetry Events”

$ iex
warning: the :loggers configuration for MyApp.Repo is deprecated.

  * To customize the log level, set log: :debug | :info | :warn | :error instead
  * To disable logging, set log: false instead
  * To hook into logging events, see the "Telemetry Events" section in Ecto.Repo docs

  lib/ecto/repo/supervisor.ex:76: Ecto.Repo.Supervisor.compile_config/2
  lib/my_app/repo.ex:2: (module)

We recommend adapters to publish certain Telemetry events listed below.


  # config/prod.secret.exs

  config :my_app, MyApp.Repo,
    # ...
-   loggers: [Appsignal.Ecto, Ecto.LogEntry]


to enable query logging in AppSignal back again:

If you’re using Ecto 3, attach Appsignal.Ecto to Telemetry query events in your application’s start/2 function.

  # lib/my_app/application.ex

  def start(_type, _args) do
    import Supervisor.Spec

+   :telemetry.attach(
+     "appsignal-ecto",
+     [:my_app, :repo, :query],
+     &Appsignal.Ecto.handle_event/4,
+     nil
+   )

    # start supervision tree



make sure to start ecto_sql instead of ecto in MyApp.ReleaseTasks module:

  # lib/my_app/release_tasks.ex

  @start_apps [
-   :ecto
+   :ecto_sql

  # ...

or else telemetry application won’t be started either and you’ll get this error if any Ecto.LogEntry is attempted to be logged when running pending migrations:

[172.XXX.XXX.XX] module=DBConnection [error] an exception was raised logging
%DBConnection.LogEntry{...}: ** (ArgumentError) argument error
[172.XXX.XXX.XX]     (stdlib) :ets.lookup(Telemetry.HandlerTable, [:my_app, :repo, :query])
[172.XXX.XXX.XX]     (telemetry) lib/telemetry/handler_table.ex:59: Telemetry.HandlerTable.list_for_event/1
[172.XXX.XXX.XX]     (telemetry) lib/telemetry.ex:76: Telemetry.execute/3
[172.XXX.XXX.XX]     (ecto_sql) lib/ecto/adapters/sql.ex:756: Ecto.Adapters.SQL.log/4
[172.XXX.XXX.XX]     (db_connection) lib/db_connection.ex:1303: DBConnection.log/5
[172.XXX.XXX.XX]     (db_connection) lib/db_connection.ex:1359: DBConnection.run_transaction/4
[172.XXX.XXX.XX]     (ecto_sql) lib/ecto/migrator.ex:184: Ecto.Migrator.do_run_maybe_in_transaction/3
[172.XXX.XXX.XX]     (elixir) lib/task/supervised.ex:89: Task.Supervised.do_apply/2