Query Optimization with Index not being considered

MongoDB Atlas
2

It seems like you’re experiencing some performance issues with your MongoDB query despite adding an index hint. Let’s break down your query and see if we can optimize it further:

  1. Filter Criteria: Your query filters documents based on the activityType, createdAt, and _id fields. Make sure that these fields are indexed properly.
  2. Index Hint: You’ve provided an index hint for { activityType: 1, createdAt: 1, _id: 1 }. This should help MongoDB choose the correct index for your query.
  3. Sorting: You’re sorting the results by createdAt and _id, both in descending order. Sorting can be expensive, especially when dealing with large datasets.
  4. Limit: You’re limiting the results to 10 documents, which is good for performance.

Given that your query has examined a large number of keys and documents, here are a few suggestions:

  • Index Optimization: Double-check that your indexes are optimized for the query. Ensure that the fields you’re querying, filtering, and sorting on have appropriate indexes.
  • Review Sorting: Sorting on multiple fields can be costly. Consider if both createdAt and _id need to be sorted or if you can optimize the sorting logic.
  • Data Volume: If your collection has a very large number of documents, even with proper indexing, some queries may still require a significant amount of resources. In such cases, consider sharding or other scaling strategies.
  • Query Patterns: Analyze your query patterns and usage scenarios. Sometimes, restructuring data or adjusting queries can significantly improve performance.

If you continue to experience performance issues, you might want to consider reaching out to MongoDB’s support or community forums for more in-depth assistance tailored to your specific use case.

CODE :

{
  "filter": {
    "activityType": {
      "$in": ["buy", "win_auction", "list", "create_auction"]
    },
    "createdAt": {
      "$gt": { "$date": "2023-06-26T23:59:59.999Z" }
    },
    "_id": { "$lt": { "$oid": "649a696323094096e4d74015" } }
  },
  "sort": { "createdAt": -1 },
  "limit": 10,
  "collation": { "locale": "en_US" }
}

**Adjustments made:**

**Removed _id from Sort:** Since we're already querying based on _id in the filter criteria, we don't necessarily need to sort by it. Removing _id from the sorting stage may reduce the complexity of the query.

**Removed Index Hint:** In some cases, MongoDB's query optimizer may perform better without an index hint, especially if the provided hint isn't optimal for the query. Removing the hint allows MongoDB to choose the best index based on its statistics and query plan.

By simplifying the sorting stage and removing the index hint, we aim to improve the query’s performance. However, it’s essential to monitor the query’s execution after these changes to ensure they have the desired effect. If you still encounter performance issues, further optimization or analysis of the data and indexes may be necessary.