Resuming Change Streams After Interruption
Learners will persist the resume token and restart a change stream from the last processed event to guarantee at-least-once delivery.
The Problem: What Happens After a Crash?
A change stream consumer process can be interrupted by network failures, deployments, crashes, or intentional restarts. Without a mechanism to resume from the last processed event, your application would restart the stream from the current moment and miss all events that occurred during the downtime. MongoDB's resume tokens solve this problem by letting you reopen a stream from an exact position in the oplog history.
What Is a Resume Token?
Every change event document has an _id field that serves as its resume token—a binary opaque value that uniquely identifies the event's position in the oplog. It looks like { _data: '...' } where the data is a hex-encoded internal identifier. You do not need to understand its contents; you only need to save it and pass it back to MongoDB to resume from that exact position.
// A resume token is the _id field of a change event
// Example structure (your values will differ):
// {
// _id: {
// _data: '8264CE3B7200000002463C6F5A100...'
// }
// }
// Store it as-is — do not parse or modify the _data valueAll lessons in this course
- Opening a Change Stream on a Collection
- Change Event Document Structure
- Filtering Events With an Aggregation Pipeline
- Resuming Change Streams After Interruption