Saturn

A child-eating monster; a library to help you find and eliminate N+1 queries.

Usage

In order for Saturn to collect query data, it first must be installed. Once that is completed, you may use the following functions:

By default, Saturn starts disabled (i.e. not collecting query data) to save memory. When you'd like to start collecting query data, run:

Saturn.enable()

You can also configure Saturn to be enabled at start-up using the enable key of its configuration:

config :saturn, enable: true

To stop collecting query data, run:

Saturn.disable()

Once you have collected some data, you can query the most-made queries:

iex> Saturn.report()
Query: "SELECT DISTINCT o0.\"queue\" FROM \"public\".\"oban_jobs\" AS o0 WHERE (o0.\"state\" = 'available') AND (NOT (o0.\"queue\" IS NULL))"
Count: 100
Stacktrace:
  lib/ecto/repo/supervisor.ex:162: Ecto.Repo.Supervisor.tuplet/2
  lib/my_app/repo.ex:2: MyApp.Repo.all/2
  lib/oban/plugins/stager.ex:131: Oban.Plugins.Stager.notify_queues/1
  lib/oban/plugins/stager.ex:98: Oban.Plugins.Stager.-check_leadership_and_stage/1-fun-0-/1
  lib/ecto/adapters/sql.ex:1202: Ecto.Adapters.SQL.-checkout_or_transaction/4-fun-0-/3
  ...
#=> :ok

Invoking Saturn.report() as Saturn.report(:count) is equivalent; the argument defaults to :count.

Saturn also supports querying by time:

iex> Saturn.report(:time)
Query: "SELECT DISTINCT o0.\"queue\" FROM \"public\".\"oban_jobs\" AS o0 WHERE (o0.\"state\" = 'available') AND (NOT (o0.\"queue\" IS NULL))"
Time: 157 ms
Stacktrace:
  lib/ecto/repo/supervisor.ex:162: Ecto.Repo.Supervisor.tuplet/2
  lib/my_app/repo.ex:2: MyApp.Repo.all/2
  lib/oban/plugins/stager.ex:131: Oban.Plugins.Stager.notify_queues/1
  lib/oban/plugins/stager.ex:98: Oban.Plugins.Stager.-check_leadership_and_stage/1-fun-0-/1
  lib/ecto/adapters/sql.ex:1202: Ecto.Adapters.SQL.-checkout_or_transaction/4-fun-0-/3
  ...
#=> :ok

Lastly, Saturn supports a prof-style output (a la eprof, fprof, etc) to help you identify cost centers:

iex> Saturn.report(:prof)
Source                                                                   Count %Count     Time %Time
Saturn.fake/1                                                                2     66   246.91    95
  SELECT * FROM users;                                                       2     66   246.91    95
Saturn.foobar/2                                                              1     33    12.35     4
  Saturn.Foobar.do_thing/3                                                   1     33    12.35     4
    SELECT * FROM users WHERE id = 5;                                        1     33    12.35     4

If you want to clear all recorded queries, invoke Saturn.clear/0:

Saturn.clear()
#=> :ok

Installation

The package can be installed by adding saturn to your list of dependencies in mix.exs:

def deps do
  [
    {:saturn, git: "[email protected]:instinctscience/saturn.git"}
  ]
end

Next, your application needs to be configured to send Ecto telemetry events to Saturn:

# lib/myapp_web/telemetry.ex

:ok =
  :telemetry.attach(
    "saturn-aggregator",
    [:myapp, :repo, :query],
    &Saturn.handle_query/4,
    nil
  )

Remember to change :myapp to the actual name of your app!

Finally, in order for Saturn to collect and report stacktraces, Ecto needs to be configured to include stacktraces in its telemetry events:

# config/dev.exs

config :myapp, :repo,
  username: "postgres",
  password: "postgres",
  # etc
  stacktrace: true