Understanding Cookie, Session, TempData, ViewBag & ViewData in MVC – Uses, Differences & Performance

ASP.NET MVC provides multiple ways to store and transfer data between requests and views. Each mechanism serves a specific purpose, has different lifetimes, and impacts performance differently.

This article explains:

• What Cookie, Session, TempData, ViewBag, and ViewData are

• When to use each

• Performance impact

• Which one is best for performance

• Comparison table

1. Cookie

What it is

A cookie is a small piece of data stored in the user's browser .
It is sent with every request to the server.

Lifetime

You define it — minutes, days, or months.

When to use

✔ To store small data that must persist across requests, even after browser restart
✔ Remember user preferences (theme, language)
✔ Track login status (auth cookie)

Performance

• Very efficient for the server (stored on client side)

• But large cookies slow down requests (added to every HTTP call)

• Should keep size < 4 KB

2. Session

What it is

Session stores data on the server , specific to each user.

Lifetime

Until browser closes or session timeout (default 20 minutes).

When to use

✔ Temporary user state like cart items, user ID, tokens
✔ Sensitive data (not safe to store in cookie)

Performance

• Heavy on server memory

• Too many sessions may affect performance

• Expensive in load-balanced environments unless using distributed session state

3. TempData

What it is

Stores data for one request , or until it is read once.
Used internally with Session.

When to use

✔ Redirect scenarios
✔ Show success/error messages after POST → Redirect → GET
✔ Passing data between two controller actions

Performance

• Stored in Session, so cost is similar

• But used temporarily and lightweight

4. ViewBag

What it is

A dynamic wrapper around ViewData.
Used to pass data from Controller to View only.

Lifetime

Only for current request .

When to use

✔ Small, non-important data
✔ Title, dropdown lists, flags, UI messages

Performance

• Stored in memory

• Very lightweight

• Faster than Session/TempData

• Not for large objects

5. ViewData

What it is

A dictionary-based structure for sending data from Controller to View .

Lifetime

Only during the request.

When to use

✔ Same as ViewBag, but strongly-typed access is missing
✔ Good for passing small data collections

Performance

• Also lightweight

• Similar to ViewBag in performance

Performance Comparison (Best to Worst)

Feature	Storage	Lifetime	Performance	Best Use
ViewBag	Memory	Request	★★★★★ (fastest)	Pass small data to a view
ViewData	Memory	Request	★★★★★	Same as above
TempData	Session	1–2 requests	★★★☆☆	Redirect scenarios
Cookie	Browser	Custom	★★★☆☆ (depends on size)	Persist data on browser
Session	Server memory	Minutes	★★☆☆☆ (heaviest)	User-specific data

Which One Is Best for Performance?

Fastest

✅ ViewBag / ViewData (request-level only, no persistence)

Good-performance and persistent

✅ Cookie (small data only)

Heavy / avoid unless needed

❌ Session (high memory cost)

When Should You Use What? (Simple Guide)

Scenario	Best Choice
Keep user logged in	Cookie
Shopping cart	Session
Display success message after redirect	TempData
Pass dropdown data to view	ViewBag / ViewData
Store theme or language preference	Cookie
Pass small data from controller to view	ViewBag