Remove outdated comound indexes that change often (increment)-CodePudding

I have a user document with structure like this

email: string
version: number
username: string

And this user collection has following indexes

collection.createIndex({email: 1}, {unique: true})
collection.createIndex({email: 1, version: 1})

First index ensures that email is unique and second one allows for more efficient lookup and updates when queries like this one are executed

collection.updateOne({email: "...", version: 2}, data)

My concern is this - every time user document is updated it's version is incremented. Does this mean that there is now an index for each combination of email-version? Which means that with time such index will occupy a lot of resources. Is it possible to make mongo remove old email-version index once version changes (as it can only be incremented)?

CodePudding user response：

Indexes are implemented on the storage engine side. Mongo just uses them. In case of wiredtiger, it's b-tree for regular indexes. Any document update which changes indexed field results with deletion of previous node in the tree and insertion of the new one.