Caching strategies in FastAPI - Performance & Optimization

Performance: Caching strategies

HIGH IMPACT

Caching strategies improve page load speed by reducing server processing and network delays for repeated requests.

Serving frequently requested API data

FastAPI

from fastapi import FastAPI
from fastapi_cache import FastAPICache
from fastapi_cache.backends.inmemory import InMemoryBackend
from fastapi_cache.decorator import cache

app = FastAPI()

@app.on_event('startup')
async def startup():
    FastAPICache.init(InMemoryBackend())

@app.get('/data')
@cache(expire=60)
async def get_data():
    data = await fetch_data_from_db()
    return data

Caches the response for 60 seconds, serving repeated requests instantly without hitting the database.

📈 Performance GainReduces server processing time to near zero for cached requests, improving LCP and reducing CPU load

Serving frequently requested API data

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/data')
async def get_data():
    # Fetch fresh data every request
    data = await fetch_data_from_db()
    return data

Fetching data from the database on every request causes slow responses and high server load.

📉 Performance CostBlocks response for database query time on every request, increasing LCP and server CPU usage

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No caching, fetch fresh data every request	Minimal DOM nodes	Multiple reflows due to slow response	High paint cost due to delayed content	[X] Bad
Cache API responses for repeated requests	Minimal DOM nodes	Single reflow with fast response	Low paint cost with quick content display	[OK] Good

Rendering Pipeline

Caching reduces server response time, allowing the browser to receive content faster and start rendering sooner.

→Network

→Server Processing

→First Paint

⚠️ BottleneckServer Processing time waiting for data fetch

Core Web Vital Affected

LCP

Caching strategies improve page load speed by reducing server processing and network delays for repeated requests.

Optimization Tips

1Cache frequently requested data to reduce server processing time.

2Set appropriate cache expiration to balance freshness and performance.

3Use server-side caching to improve Largest Contentful Paint (LCP).

Performance Quiz - 3 Questions

How does caching API responses affect Largest Contentful Paint (LCP)?

A It improves LCP by reducing server response time.

B It worsens LCP by adding extra processing.

C It has no effect on LCP.

D It only affects layout shifts, not LCP.

DevTools: Network

How to check: Open DevTools, go to Network tab, reload the page or API call, and observe response times and status codes.

What to look for: Look for faster response times and 200 status codes with cache headers indicating cached responses.