mongodb capped collections

MongoDB capped collections are a type of MongoDB collection that have a fixed size and follow a "first-in, first-out" (FIFO) order. Capped collections are useful for scenarios where you want to store a fixed amount of data, such as log data or event streams, and where the oldest data can be discarded as new data is added.

Capped collections have a number of unique properties that make them different from regular collections in MongoDB:

1. Fixed size: Capped collections have a fixed size that you specify when you create the collection. Once the collection reaches this size, new data will overwrite the oldest data in the collection.

2. Insert order: Capped collections preserve the order in which documents are inserted, and always return documents in the order in which they were inserted.

3. Automatic index on insertion order: Capped collections automatically create an index on the insertion order, which can be used to optimize queries that retrieve documents in the order they were inserted.

To create a capped collection in MongoDB, you can use the db.createCollection() method with the capped: true option, and specify the maximum size of the collection in bytes:

db.createCollection("myCappedCollection", { capped: true, size: 100000 });

In this example, we're creating a capped collection called "myCappedCollection" with a maximum size of 100,000 bytes (or 100 KB). Once the collection reaches this size, new data will overwrite the oldest data in the collection.

Capped collections can be useful for scenarios where you want to store a fixed amount of data and don't need to perform complex queries on the data. However, it's important to note that capped collections do not support updates or deletions, and do not automatically free up space when data is removed. Therefore, capped collections are not appropriate for all use cases, and it's important to carefully consider the pros and cons before deciding whether to use them.