Recently I started using logger_file_backend to log the info level logs to the file which then is getting used for Kibana through Elasticsearch.
While doing performance testing we encountered a slowness issue when we enable the logger_file_backend.

I am able to reproduce the same issue in my local with the following Logger configuration:

    config :logger,
      backends: [
        :console,
        {LoggerFileBackend, :test}
      ]
    
    config :logger, :console,
      format: "[$level] $message\n",
      level: :info,
      sync_threshold: 100,
      discard_threshold: 500
    
    config :logger, :test,
      metadata: [:request_id, :user_id, :api],
      path: "./log/test.log",
      level: :info

I have created a simple “hello world” API to check the performance and ran it using Apache benchmarking tool : ab -k -c 500 -n 500 http://localhost:4000/api/v1/hello

In the output I can see following response time:

[info] Sent 200 in 30ms
[info] Sent 200 in 30ms
[info] Sent 200 in 30ms
[info] Sent 200 in 30ms
[info] Sent 200 in 30ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms 
[info] Sent 200 in 32ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms
[info] Sent 200 in 31ms

When I am disabling the LoggerFileBackend in :backends then for the same test I am getting following results:

[info] Sent 200 in 4ms
[info] Sent 200 in 5ms
[info] Sent 200 in 4ms
[info] Sent 200 in 4ms
[info] Sent 200 in 5ms
[info] Sent 200 in 5ms
[info] Sent 200 in 5ms
[info] Sent 200 in 5ms

It seems like file writing is taking more time and the messages are getting piled up in the logger queue.
I have tried out with multiple settings of :sync_threshold & :discard_threshold but nothing seems to optimize the performance.

I am using following elixir and erlang version for my demo phoenix application:
elixir 1.13.4-otp-23 erlang 23.2.1

Can anyone tell how we can optimize this to even save the :debug level logs in the file as we do not want to loose the logs?
Please also suggest any other alternate way to do the same without sacrificing performance if possible.