Working with Capped Collection in MongoDB by Mahi Panchal

 Working with Capped Collections in MongoDB

When working with large-scale, high-throughput systems, efficient data storage and retrieval becomes critical. One of MongoDB’s powerful features that helps with this is the capped collection. If you’ve never used it before or want a refresher, this post will guide you through what capped collections are, when to use them, and how to create and interact with them.

What is a Capped Collection?

A capped collection is a fixed-size collection that maintains the insertion order of documents. Once the allocated space is full, it overwrites the oldest documents with new ones — think of it as a circular buffer.

It’s especially useful when you need to store logs, stream data, or any other time-based information where you only care about the most recent records.

Key Features

Fixed size: You define the maximum size or document count.

High performance: Because of its fixed size and append-only nature.

Auto deletion: Older documents are automatically removed when the cap is reached.

Insertion order: Documents are stored in the order they were inserted.

When Should You Use It?

Use capped collections when:

You’re building a logging system, like for API request logs.

You need real-time analytics with recent data.

You want to limit storage without manual cleanup.

You want fast, efficient writes with a rolling window of data.

Creating a Capped Collection

Inserting and Reading from It

Inserting is the same as a normal collection:

Reading keeps the insertion order:

To get the latest entries:

Things to Keep in Mind:

No document updates that increase size: You can update a document, but only if it doesn't make it larger.

No deletions: You can’t manually delete docs — MongoDB handles that.

No schema changes: You can’t convert a normal collection to capped or vice versa (unless you recreate it).

Final Thoughts

Capped collections are like the "stories" feature in social media — temporary, always fresh, and perfect for the now. They’re not for storing everything forever, but when you need speed, structure, and simplicity, they’re a smart choice.

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Mahi Panchal

University: Shree Balaji University, Pune

School: School of Computer Studies

Course: BCA (Bachelor of Computer Applications)

Interests: NoSQL, MongoDB, and related technologies

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