Traditional Pagination Query

db.users
  .find(conditions)
  .sort({ _id: -1 })
  .skip((page - 1) * numberOfPage)
  .limit(numberOfPage);

The code above is a traditional, unoptimized pagination query based on page number and page size. The obvious drawback is that skip() must scan past the skipped documents, so it degrades badly on large collections.

Optimization

Typically the frontend passes a page number to the backend. Instead, the common optimization is to use a unique, indexed value as the query condition rather than skip(). The natural choice is _id: keep the _id of the last document from the previous page and query for documents whose _id is less than it.

// lastId is the _id of the last document from the previous page
db.users
  .find({ _id: { $lt: lastId }, ...conditions })
  .sort({ _id: -1 })
  .limit(numberOfPage)

ObjectID

I originally wrote quite a bit more here, but then found someone had already written a better article explaining ObjectID, so I'll defer to that.

• Article link