Inconsistent Document Updates with updateMany and arrayFilters in Shared MongoDB Collection

Ops and Admin Sharding
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1

Hello MongoDB Community,

I’m experiencing an issue with the updateMany operation using arrayFilters in my shared MongoDB collection. My documents contain an array field, and I’m trying to update specific elements within these arrays based on certain conditions. However, I’m seeing inconsistent results.

For example, I have a query that should update 10 documents, but it sometimes updates only 5, 6, or even just 3 documents. Occasionally, it updates all the documents as expected. I have verified that all the documents match the query conditions, so I’m not sure why this inconsistency is happening.

Here’s a simplified version of my query:

db.collection.updateMany(
  { /* match documents */ },
  { 
    $set: { "arrayField.$[element].fieldToUpdate": "newValue" } 
  },
  {
    arrayFilters: [ { "element.someCondition": { $eq: true } } ]
  }
);

Additional Context:

  • The arrayField contains a maximum of 8 elements in each document.
  • I am using a shared collection where other update operations might be happening concurrently.
  • All documents should have the same structure, and I have verified the conditions should match all targeted documents.
  • I have checked the query and filter conditions, and they seem to be correct.

Questions:

  1. What could cause this inconsistent update behavior with updateMany and arrayFilters?
  2. Are there any known issues or limitations when using arrayFilters with shared collections?
  3. What best practices should I follow to ensure that all intended documents are updated?

Any insights or suggestions on how to troubleshoot or resolve this issue would be greatly appreciated!

Thank you!

2

One reason that a matching document is not updated even if it matches is if …fieldToUpdate already has the value newValue.

Please share the real update statement and real sample documents that are not updated.