How to Optimize JSON Data Retrieval Speed in FastAPI?

Optimizing JSON Data Retrieval Speed in FastAPI

The sluggish return of a sizable JSON payload from FastAPI's GET endpoint is a recurring issue. When using json.dumps() to transmit data from a file using json.loads(), the response is vastly delayed. While return data can be used to send data to the user, is there a more efficient approach?

Problem:
The processing pipeline initially transforms the data into JSON using pandas' to_json() function, then loads it into a dictionary with json.loads(), and finally translates it back to JSON. This multi-step conversion process introduces substantial latency.

Proposed Solution:

First, it is crucial to recognize that FastAPI converts return values into JSON-compatible data using the jsonable_encoder, followed by serialization using the standard Python's json.dumps() function. This two-step process is known to be slow.

Option 1: Utilize Alternative JSON Encoders
Consider using alternative JSON encoders like orjson or ujson. These encoders outperform the default jsonable_encoder and json.dumps() combination.

Option 2: Direct Return of Custom Response
For optimal performance, use the custom APIRoute class and return a Response object. This bypasses FastAPI's default JSON conversion process.

<code class="python">from fastapi.routing import APIRouter, APIRoute

class TimedRoute(APIRoute):
    ...

app = FastAPI()
router = APIRouter(route_class=TimedRoute)

@router.get("/custom-response")
def get_data():
    df = pd.read_parquet('data.parquet')
    return Response(df.to_json(orient="records"), media_type="application/json")

app.include_router(router)</code>

Additional Considerations:

• Streaming Responses: Consider using stream responses if handling exceptionally large datasets can cause out-of-memory issues.
• Dask Library: Utilize Dask to efficiently process large amounts of data. Convert the resulting Dask DataFrame to a Pandas DataFrame before using .to_json().
• File Download: Set the Content-Disposition header to indicate that the response should be downloaded as a file, bypassing browser rendering delays.

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