Inefficient column deletion

[mtrezza]

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Issue Description

Removing a column from a class via Parse Dashboard is inefficient and can potentially impact a production system.

A column is removed by calling updateMany (for the MongoDB storage adapter) on the entire collection which is a simple but inefficient way to delete a field. It causes a collection scan through all documents, even if only 1 document has the field which should be removed.

parse-server/src/Adapters/Storage/Mongo/MongoStorageAdapter.js

Line 443 in 3bd5684

.then((collection) => collection.updateMany({}, collectionUpdate))

Steps to reproduce

1. Create a collection with millions of documents.
2. Delete a column via Parse Dashboard.
3. Notice the DB impact.

Expected Results

Deleting should make use of indices. This would only update the document that actually contain the field to remove.

Actual Outcome

Deleting does not make use of indices and causes collection scan.

Suggested solution

Add query filter to updateMany command to allow for index scan:

• For an index to be used when deleting a field, it has to be manually created (auto-creating an index can impact a production system if not properly prepared).
• The required index to create is: { <fieldNameToDelete>: { $exists: true } }.

Possible Improvements

The index could be temporarily created and deleted afterwards, however this would need to be optional in the Parse Dashboard since index creation itself can also have a performance impact on the DB.

Environment Setup

• Server
  • parse-server version (Be specific! Don't say 'latest'.) : 4.2.0