Mongo DB collection size not changed after removal of fields from document

Question

To reduce my existing collection size, I have removed some unwanted fields from the documents from the collection. After and before I ran the collection stats to check the size, but it never changed. I am missing some thing (like update anything) to reflect the reduced size in my stats, Please advice me. I am running this in my local PC, not having any other nodes. Thank you.

Answer 1

This is correct behavior. The only time mongo releases disk space is when you drop a database or do a repair. (see here)

prettier explanation here

Basically, mongodb keeps any space it has allocated unless and until you drop a database or do a repair. It does this because adding space is not efficient, it is time-consuming. So once it has it, it keeps it and uses the blank space created until there is none left and then it gets more.

Answer 2

As mentioned by Daniel F in a comment on the question, this worked for me in the mongo shell:

use your-database-name
db.runCommand({ compact: "your-collection-name" })