Catapult

This is a collection of tracing backends for ocaml-trace, ultimately producing Catapult/TEF trace format.

The traces are .json files (or compressed .json.gz). They can be viewed in:

• https://ui.perfetto.dev/
• chrome://tracing in chrome/chromium
• https://github.com/wolfpld/tracy after conversion (the tracy-import-chrome binary)

Usage

Instrument your code using ocaml-trace. In the program's entry point, use one of the Catapult libraries backend to forward events from Trace into the place of your choice.

An example can be found in examples/heavy/heavy.ml.

sqlite

To collect data directly into a local Sqlite database, use something like:

let main () =̵
  …
  let@ writer = Catapult_sqlite.Writer.with_ ~file:!db ~sync:!sync () in
  Trace.setup_collector (Catapult_sqlite.trace_collector_of_writer writer);

  …
  (* do the actual work here *)

(assuming this is in scope:

let (let@) = (@@)

)

network client

The library catapult-client provides a tracing backend that forwards all events (messages, traces, metrics) to a network daemon. The daemon is in the catapult-daemon package.

The traces can be listed and retrieved using the catapult-conv program that comes with catapult-sqlite.

Systemd

An example systemd service file for this daemon can be found in src/data/catapult-daemon.service.

[Unit]
Description=Catapult daemon (receives and stores profiling traces)

[Socket]
ListenStream=6981
Accept=no

[Service]
ExecStart=catapult-daemon --addr=tcp://127.0.0.1:6981
Restart=always
RestartSec=10

[Install]
WantedBy=default.target

Example: "basic"

A very stupid example (in examples/basic/basic.ml), is:

let (let@) = (@@)
let spf = Printf.sprintf

let rec fake_trace depth =
  if depth>=3 then ()
  else (
    (* the probe is here *)
    let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "step" in
    Thread.delay 0.1;
    Printf.printf "fake (depth=%d)\n%!" depth;
    fake_trace (depth+1);
    Thread.delay 0.2;
    Trace.message "iteration.done" ~data:(fun () -> ["depth", `Int depth]);
  )

let () =
  (* address of daemon *)
  let addr = Catapult_client.addr_of_string_exn "tcp://localhost:1234" in
  let@() = Catapult_client.with_ ~addr () in
  let n = try int_of_string (Sys.getenv "N") with _ -> 10 in
  Printf.printf "run %d iterations\n%!" n;

  for _i = 1 to n do
    fake_trace 0;
  done

Once opened in chrome://tracing, the trace looks like this:

Example: "heavy"

A more heavy example (used to benchmark a bit the tracing), is in examples/heavy.

In a terminal, run the daemon (if it's not already running):

$ ./daemon.sh

Then in another terminal:

$ ./heavy.sh -n=1 --mode=net -j 2 --trace-id=mytrace
use net client tcp://127.0.0.1:6981
run 1 iterations
iteration 1
use net client tcp://127.0.0.1:6981
run 1 iterations
iteration 1

# list traces
$ catapult-conv -l
[…]
mytrace.db

# convert last trace into a file (trace.json.gz)
$ catapult-conv mytrace.db

$ ls -lh trace.json.gz 
-rw-r--r-- 1 simon simon 374K Feb 16 11:38 trace.json.gz

Opened in chrome, the trace looks like that (focusing on a "step" event):

Coverage

• duration events
• async events
• flow events
• instants
• metadata
• counters
• object events
• contexts
• memory dumps
• mark events
• clock synchro

License

MIT