Make autoIndex syncIndex instead of createIndex

[GustavoOS]

Prerequisites

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🚀 Feature Proposal

autoIndex will check existing indexes instead of re-creating indexes everytime the app runs

Motivation

Mongoose docs explains that autoIndex is not advised to production environments because it creates indexes everytime the app runs. This makes the process of introducing indexes tricky in production. Mongoose offers synIndexes, but this has to be called individually for each model.

Example

No response

[vkarpov15]

You can use Connection.prototype.syncIndexes(): https://mongoosejs.com/docs/api/connection.html#Connection.prototype.syncIndexes() . For example, await mongoose.connection.syncIndexes()

We won't make autoIndex use syncIndexes by default for now, because that's potentially expensive and risky (unintentional deletion of index can cause serious performance issues) but we can add an option to make autoIndex use syncIndexes()

[vkarpov15]

@hasezoey @AbdelrahmanHafez what do you think, is it worthwhile to add a separate option to make autoIndex use syncIndexes() under the hood? I'm not entirely convinced because await mongoose.connection.syncIndexes() is already a one-liner, the option wouldn't make things particularly cleaner.

[hasezoey]

@hasezoey @AbdelrahmanHafez what do you think, is it worthwhile to add a separate option to make autoIndex use syncIndexes() under the hood? I'm not entirely convinced because await mongoose.connection.syncIndexes() is already a one-liner, the option wouldn't make things particularly cleaner.

Personally, i dont mind if there would be a extra option to use syncIndexes instead, as long as it is not the default for autoIndex or at least wait until the next major version for that.
Maybe a different option like syncIndex, or allow autoIndex to be a string to be set to bool | 'createIndexes' | 'syncIndexes' (where bool is backwards compatible to createIndexes and any non-proper value either give a error, or a warning and treat it as false; maybe also check it lowercased?), which i think would be cleaner than doing a nested object or another option which would be mutually exclusive.

[GustavoOS]

Well, the semantics of auto index is "mongoose will take care of index for you". But this isn't true simply because this option should never be used in production (as stated in current docs) as it tries to recreate indexes as many times as possible.
The purpose of this feature request is to make autoIndex actually useful and meaningful, in a way it can be used in production.

As this should not be used in production, the change of behaviour would not break previous code.