osprofiler/doc/source/api.rst

API

There are a few things that you should know about API before using it.

Four ways to add a new trace point.

from osprofiler import profiler

def some_func():
    profiler.start("point_name", {"any_key": "with_any_value"})
    # your code
    profiler.stop({"any_info_about_point": "in_this_dict"})


@profiler.trace("point_name",
                info={"any_info_about_point": "in_this_dict"},
                hide_args=False)
def some_func2(*args, **kwargs):
    # If you need to hide args in profile info, put hide_args=True
    pass

def some_func3():
    with profiler.Trace("point_name",
                        info={"any_key": "with_any_value"}):
        # some code here

@profiler.trace_cls("point_name", info={}, hide_args=False,
                    trace_private=False)
class TracedClass(object):

    def traced_method(self):
        pass

    def _traced_only_if_trace_private_true(self):
         pass

How profiler works?

• @profiler.Trace() and profiler.trace() are just syntax sugar, that just calls profiler.start() & profiler.stop() methods.

• Every call of profiler.start() & profiler.stop() sends to collector 1 message. It means that every trace point creates 2 records in the collector. (more about collector & records later)

• Nested trace points are supported. The sample below produces 2 trace points:

  profiler.start("parent_point")
  profiler.start("child_point")
  profiler.stop()
  profiler.stop()

  The implementation is quite simple. Profiler has one stack that contains ids of all trace points. E.g.:

  profiler.start("parent_point") # trace_stack.push(<new_uuid>)
                                 # send to collector -> trace_stack[-2:]
  
  profiler.start("parent_point") # trace_stack.push(<new_uuid>)
                                 # send to collector -> trace_stack[-2:]
  profiler.stop()                # send to collector -> trace_stack[-2:]
                                 # trace_stack.pop()
  
  profiler.stop()                # send to collector -> trace_stack[-2:]
                                 # trace_stack.pop()

  It's simple to build a tree of nested trace points, having (parent_id, point_id) of all trace points.

Process of sending to collector.

Trace points contain 2 messages (start and stop). Messages like below are sent to a collector:

{

"name": <point_name>-(start|stop) "base_id": <uuid>, "parent_id": <uuid>, "trace_id": <uuid>, "info": <dict>

}

The fields are defined as the following:

• base_id - <uuid> that is equal for all trace points that belong to one trace, this is done to simplify the process of retrieving all trace points related to one trace from collector
• parent_id - <uuid> of parent trace point
• trace_id - <uuid> of current trace point
• info - the dictionary that contains user information passed when calling profiler start() & stop() methods.

Setting up the collector.

The profiler doesn't include a trace point collector. The user/developer should instead provide a method that sends messages to a collector. Let's take a look at a trivial sample, where the collector is just a file:

import json

from osprofiler import notifier

def send_info_to_file_collector(info, context=None):
    with open("traces", "a") as f:
        f.write(json.dumps(info))

notifier.set(send_info_to_file_collector)

So now on every profiler.start() and profiler.stop() call we will write info about the trace point to the end of the traces file.

Initialization of profiler.

If profiler is not initialized, all calls to profiler.start() and profiler.stop() will be ignored.

Initialization is a quite simple procedure.

from osprofiler import profiler

profiler.init("SECRET_HMAC_KEY", base_id=<uuid>, parent_id=<uuid>)

SECRET_HMAC_KEY - will be discussed later, because it's related to the integration of OSprofiler & OpenStack.

base_id and trace_id will be used to initialize stack_trace in profiler, e.g. stack_trace = [base_id, trace_id].

OSProfiler CLI.

To make it easier for end users to work with profiler from CLI, osprofiler has entry point that allows them to retrieve information about traces and present it in human readable from.

Available commands:

• Help message with all available commands and their arguments:

  $ osprofiler -h/--help

• OSProfiler version:

  $ osprofiler -v/--version

• Results of profiling can be obtained in JSON (option: --json) and HTML (option: --html) formats:

  $ osprofiler trace show <trace_id> --json/--html

  hint: option --out will redirect result of osprofiler trace show in specified file:

  $ osprofiler trace show <trace_id> --json/--html --out /path/to/file