📝 Update docs for ORJSONResponse with details about improving performance

[falkben]

Update docs to mention to explicitly return a Response when thinking about performance. Currently the docs say to use orjson for speed, but then demonstrate returning a dictionary, which in my experience can be very slow. The main speed improvement I have found is in returning Responses directly, which avoids the call to jsonable_encoder.

Below are results from some tests I did with 7MB+ json data. These are real world and include round trips to the database so to see such a huge effect is rather amazing to me.

To be clear, the difference here is just returning an explicit ORJSONResponse object, vs. JSONResponse object vs. a dict and letting fastapi inspect it. The data returned are exactly the same in all cases.

For more examples w/ code demonstrating the differences see here:
https://github.com/falkben/fastapi_experiments/blob/master/experiments/orjson_response.py

and some tests here:
https://github.com/falkben/fastapi_experiments/blob/master/experiments/test_orjson_response.py

In those tests I observed a 6x slowdown when returning a dictionary vs. returning a Response directly

This was also discussed in the following issue: #360

At some point it would be good to try to optimize jsonable_encoder but for now I think it would be good to at least tell people about the performance impact of returning large dictionaries.

[codecov]

Codecov Report

Merging #2615 (2106ac4) into master (278adc0) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2615   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          537       537           
  Lines        13856     13856           
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  Hits         13856     13856           

Impacted Files	Coverage Δ
docs_src/custom_response/tutorial001b.py	100.00% <100.00%> (ø)

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[github-actions]

📝 Docs preview for commit 8b3b6c4 at: https://5ff7571877e9d83cd685c1ef--fastapi.netlify.app

[github-actions]

📝 Docs preview for commit 2071f19 at: https://601eb84f0aa75d20b894c8cf--fastapi.netlify.app

[tiangolo]

Awesome, thank you @falkben! ☕

I updated the text a little bit to explain the jsonable_encoder part a bit more. Thanks for the contribution! 🚀