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在启动时只加载一次模型

使用生命周期事件，确保加载操作只执行一次

在启动时只加载一次模型 是 CoddyKit 上的免费 MLOps Academy 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 MLOps Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 MLOps Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

The Slow-Endpoint Trap

If you call joblib.load inside /predict, the model reloads on every request. That is slow and wasteful for large models. 🐢

Load It Just Once

The fix: load the model a single time when the service starts, keep it in memory, and reuse it for every prediction.

The Lifespan Hook

FastAPI gives you a lifespan function to run setup before serving and cleanup after. It is the right home for model loading.

Write an Async Context Manager

You decorate an async function with asynccontextmanager. Code before yield runs at startup; code after runs at shutdown.

from contextlib import asynccontextmanager

Stash the Model in State

Load the model at startup and save it on app.state, a shared place every request handler can reach later.

@asynccontextmanager
async def lifespan(app):
    app.state.model = joblib.load("model.joblib")
    yield

Wire It to the App

Pass your lifespan function when you create the app. Now FastAPI runs your loading code once as the server boots.

app = FastAPI(lifespan=lifespan)

Read It in the Route

Inside /predict you grab the already-loaded model from app.state. No disk read, just a fast in-memory lookup.

@app.post("/predict")
def predict(req: Request):
    model = req.app.state.model

Clean Up at Shutdown

Anything after the yield runs when the app stops, perfect for closing files or freeing GPU memory the model held.

    yield
    app.state.model = None

Faster First Request

Because loading finished at startup, even the very first user gets a fast response, not a cold-load penalty. ⚡

Watch the Worker Count

Each uvicorn worker is its own process with its own copy of the model. More workers means more memory, so size them deliberately.

Why It Matters

Loading once is a core serving optimization: it cuts latency, lowers disk I/O, and keeps memory predictable under real traffic. 📈

Quick Check

You want your model loaded exactly once when the service boots. Where should that happen?

Recap

You moved loading into a lifespan hook, stored the model on app.state, and read it per request. One load, fast responses, clean shutdown. 🙌

常见问题解答

「在启动时只加载一次模型」课时是免费的吗？

是的 — 「在启动时只加载一次模型」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 MLOps Academy 课程的其余内容，请升级到 CoddyKit PRO。 MLOps Academy 课程共包含 4 节课。

「在启动时只加载一次模型」这节课中我会学到什么？

使用生命周期事件，确保加载操作只执行一次你通过在浏览器中直接运行的动手代码来练习 MLOps Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 MLOps Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 MLOps Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 3 节课，共 4 节。

「在启动时只加载一次模型」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 MLOps Academy 课中编写并运行代码吗？

能。每节 MLOps Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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