Just tried my own advice and this unfortunately won’t work!

Docs say that

• :function - purges all messages with the “function/arity” Remember that if you want to purge log calls from a dependency, the dependency must be recompiled.

So I first modified my logger config to find the logging function:

config :logger, :console,
  format: "$time\n[$level] $metadata\n$message\n\n",
  metadata: [:mfa, :file, :line]

That resulted in

[debug] mfa=Ecto.Adapters.SQL.log/4 file=lib/ecto/adapters/sql.ex line=938
QUERY OK …

But the ecto_sql library at line 938 invokes Logger.log/3 which warns that

The macros debug/2, info/2, notice/2, warning/2, error/2, critical/2, alert/2, and emergency/2 are preferred over this macro as they can automatically eliminate the call to Logger altogether at compile time if desired (see the documentation for the Logger module).

I added an explicit :debug case option to the log/4 source code in my deps folder and recompiled as instructed with mix deps.compile ecto_sql but it’s still logging?

:debug ->
  IO.puts("SQL debug")
  Logger.debug(
    fn -> log_iodata(measurements, metadata) end,
    ansi_color: sql_color(query_string)
  )

config.exs

config :logger, :console,
  format: "$time\n[$level] $metadata\n$message\n\n",
  metadata: [:mfa, :file, :line],
  compile_time_purge_matching: [
    [module: Ecto.Adapters.SQL, function: "log/4", level_lower_than: :info]
  ]

iex(1)> Repo.all(User)
SQL debug
14:02:05.547
[debug] mfa=Ecto.Adapters.SQL.log/4 file=lib/ecto/adapters/sql.ex line=939 
QUERY OK source="users" ...

Hopefully someone with more experience can provide some insight

Ok, this works, at least for me, and in my particular case.

Given log: false in the config, I made a deliberate error in a query (idd instead of id):

  def get_page_data(id) do
    Quire.Repo.one(from(p in Page, where: p.idd == ^id, select: p))
  end

Ecto failed and printed the following error:

[error] #PID<0.1021.0> running QuireWeb.Endpoint (connection #PID<0.967.0>, stream id 8) terminated
Server: localhost:4000 (http)
Request: GET /admin/pages/33
** (exit) an exception was raised:
    ** (Ecto.QueryError) lib/quire/cms.ex:186: field `idd` in `where` does not exist in schema Quire.CMS.Page in query:

from p0 in Quire.CMS.Page,
  where: p0.idd == ^33,
  select: p0

No other debug logs. At this point this probably covers 99.999% of my needs.

@KristerV Give it a try. Quite possible if it wasn’t working for you it was a bug that was solved at one point.

You should set your log level in your dev.exs file. See Logger — Logger v1.12.2 and Logger — Logger v1.12.2 for more info.

Take a look at the application configuration section of the Logger docs where it describes the :compile_time_purge_matching option. Find the corresponding Ecto function that’s printing the debug log, then just silence that module + function with level_lower_than: :info

config :logger,
  compile_time_purge_matching: [
    [module: Bar, function: "foo/3", level_lower_than: :error]
  ]

This is the beauty of Elixir separation of concerns that I’m still learning and coming across these great examples: instead of trying to cater for many different logging requirements by trying to configure Ecto, reconfigure at the Logger side!

The first thing that comes to my mind is to disable default ecto logs and provide custom handler for [:myapp, :repo, :query] telemetry events.