Ensuring consistency in pagination for frequently updated collections

I had a question regarding how to make sure pagination returns consistent results when there are frequent updates to the documents and relative ordering may change based on the sort keys.
I have considered both skip-limit and cursor based approaches and using creation timestamp as filter to deal with addition of new data but not sure how to handle it in case of updates.

  1. How do you handle pagination consistency in collections with frequent document updates, especially when those updates can affect the document’s position in the pagination order?
  2. Are there recommended patterns or strategies within MongoDB for ensuring that paginated queries return consistent and complete results, even when the underlying data is being actively updated?

The only way to have consistency is to $sort. Adding _id as the last sort key ensure a consistent order for documents where all the sort prefixes are equals.

Skip-limit has proven to be slow. Using $sort with $gt and $lt with keys of the currently viewed first and last document of the page is now the preferred way. You should be able to find examples of this with google search.

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Hello, @Priyanshu_Sharma2

Ensuring pagination consistency in MongoDB, particularly when documents are frequently updated, can be challenging. Here are some strategies to maintain consistent pagination:

Keyset Pagination: Instead of using skip-limit, keyset (or cursor-based) pagination is recommended. This method involves paginating based on the last seen item’s sort key.
Immutable Timestamps: Use immutable fields like creation timestamps as part of the sort key. This ensures that the order of documents remains consistent even if other fields are updated.
Versioning: Implement versioning for documents. When a document is updated, increase its version number. Include both the original timestamp and the version number in your sort criteria to maintain order consistency.
Snapshot Reads: Utilize snapshot reads (if using MongoDB 4.0+ with replica sets or sharded clusters) to ensure that you read from a consistent snapshot of the database, even if updates occur during pagination.
Stable Sort Keys: Choose sort keys that are less likely to change. If a field is frequently updated and used as a sort key, it can lead to inconsistencies.
Compensate for Updates: If updates are unavoidable, consider including logic in your application to detect if an update has occurred since the last page was fetched and adjust the query accordingly.
Avoid Skip: The skip method can lead to performance issues and inconsistencies, as it requires scanning through all previous documents. It’s not recommended for large datasets or systems with frequent updates.

I think what you are describing is one of the ways to implement cursor based pagination but I was concerned about the scenario where updating one of the fields which is also part of the sort keys would change the relative ordering of documents leading to same document being read multiple times or being skipped altogether as the change of ordering could cause them to be placed before or after the cursor.

It all depends on how you define consistency.

For example, when browsing documents for April 2024, do you want to see the new document or now. I want to see it. If I see it twice I am fine with that for most use case. But I want to see it at least one. If you want to avoid seeing a document twice you way always implement some kind of caching where you keep the _id of already shown documents and prune the next result set to remove those.

Dear @Ryan_Manus, you failed in the same trap as many others that tried to answer using generative AI. You cut-n-paste the whole original post, probably exactly the same cut-n-paste you feed your GenAI. But you did a little bit better as most would embolden the part before the colon.

A human would see repetition in


And your GenAI did not know that I already mentioned

So it did blindly copy the same thing.

However, I must admit that your GenAI has proposed something I did not think about:

I would like to propose a new feature to this forum.

As a tool where we can flag a post as potential a GenAI post. Then the author will have to debate if his/hers/its answer is genuine or not.

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