Measuring memory consumption - how to figure out what triggers jumps in memory?

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9

I’ve been able to figure out how to use instrument. For future references. Run a script like this to get the best information out: elixir --erl “+Muatags true” sqlite_reproduction.exs

So I ran :instrument.allocations before the query and after the query, and thse are the only significant changes that I see:

image
image666×201 11.5 KB

So this line:nif_internal: {1999, 438, 40, 10, 10, 9, 15474, 0, 0, 10, 10, 1, 0, 0, 0,
0, 0, 0}

Running with exqlite gives me no such thing:

image

For completeness here is the full script that I used:

Mix.install([
    {:ecto_sql, "~> 3.13.2"},
    {:ecto_sqlite3, "~> 0.22"},
    {:exqlite, "~> 0.33.1"}
])

Application.put_env(:myapp, Repo, database: "./dev.db")

defmodule Repo do
  use Ecto.Repo,
    otp_app: :myapp,
    adapter: Ecto.Adapters.SQLite3
end

defmodule Main do
  @sql ~s"""
  SELECT
    s0."id",
    e1."id",
    e1."type",
    e1."data",
    e1."inserted_at",
    s0."stream_id",
    s0."stream_version"
  FROM "stream_events" AS s0
  INNER JOIN "events" AS e1 ON s0."event_id" = e1."id"
  WHERE s0."stream_id" = '$all' AND s0."stream_version" >= 0
  ORDER BY s0."id" DESC
  LIMIT 1
  """

  def sqlite do
    IO.inspect "before"
    print_memory()
    save_allocations("./before_sqlite")


    {:ok, _} = Repo.start_link([])
    _s1 = Ecto.Adapters.SQL.query!(Repo, @sql, nil)

    IO.inspect "after"
    print_memory()
    save_allocations("./after_sqlite")
  end

  def exqlite do
    IO.inspect "before"
    print_memory()
    save_allocations("./before_exqlite")

    {:ok, conn} = Exqlite.Sqlite3.open("./dev.db")
    {:ok, statement} = Exqlite.Sqlite3.prepare(conn, @sql)
    {:row, _results} = Exqlite.Sqlite3.step(conn, statement)
    IO.inspect "after"
    print_memory()
    save_allocations("./after_exqlite")
  end


  defp print_memory() do
    IO.inspect "memory: #{:erlang.memory(:total) / 1_000_000}"
  end

  defp save_allocations(name) do
    {:ok, x} = :instrument.allocations
    File.write!(name, inspect(x, limit: :infinity, pretty: true))
  end
end

# Main.sqlite()
Main.exqlite()
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