An ASGI middleware that wraps the excellent yappi profiler to let you
measure the execution time of any function or coroutine in the context of
an HTTP request, and return it as a standard Server-Timing HTTP header.
Here are some example configurations for various frameworks and libraries. Feel free to combine them as needed.
fastapi_app.add_middleware(ServerTimingMiddleware, calls_to_track={
"1deps": (fastapi.routing.solve_dependencies,),
"2main": (fastapi.routing.run_endpoint_function,),
"3valid": (pydantic.fields.ModelField.validate,),
"4encode": (fastapi.encoders.jsonable_encoder,),
"5render": (
fastapi.responses.JSONResponse.render,
fastapi.responses.ORJSONResponse.render,
),
})from starlette.middleware import Middleware
middleware = [
Middleware(ServerTimingMiddleware, calls_to_track={
# TODO: ...
}),
]
starlette_app = Starlette(routes=routes, middleware=middleware)fastapi_app.add_middleware(ServerTimingMiddleware, calls_to_track={
"db_exec": (sqlalchemy.engine.base.Engine.execute,),
"db_fetch": (
sqlalchemy.engine.ResultProxy.fetchone,
sqlalchemy.engine.ResultProxy.fetchmany,
sqlalchemy.engine.ResultProxy.fetchall,
),
})Feel free to submit PRs containing examples for more libraries and ASGI frameworks.
- Only the end-to-end time is reported for both functions and coroutines,
so it's not possible to tell from the metrics when a coroutine took a long
time because the event loop thread got stalled
(though
asyncio's debug mode can help). - The profiler's memory is not freed over time, and only gets cleared when it exceeds a given threshold (50MB by default). When memory gets cleared, data collected for all ongoing requests is lost, so the timing for these will be incorrect.
- Executing the same task multiple times in parallel (such as with
asyncio.gather()) will report the duration as if they had been executed sequentially. - The minimum version of Python supported is 3.7, since this middleware makes use of PEP 567 context variables to track which function call belongs to which request, and the Python 3.6 backport doesn't have asyncio support.
- Sümer Cip (@sumerc), for creating and maintaininng yappi, as well as being very responsive and open to adding all the new features needed to make this work.
- David Montague (@dmontagu) for his involvement in shaping this middleware at every step of the way.