Use Case

As a... Node.js Driver user
I want... to abort in-progress operations
So that... I can stop waiting for and spending resources on a result that will not be used

Avoid load on DB for ignored queries.

Eg when doing a search, if the count operation takes significantly longer (eg 200ms) than finding the results to display, we can cancel it instead of just ignoring it.

Or when a client cancels their http request, we can cancel ongoing mongodb read queries for that request

User Experience

• What is the desired/expected outcome for the user once this ticket is implemented?

Being able to pass a signal parameter to queries, which would be from an AbortController.

Triggering:
 

const abort = new AbortController();
const query = db.coll("...").countDocuments(..., \{ signal: abort.signal});
abort.abort();

Dependencies

• AbortController & AbortSignal

Risks/Unknowns

• What could go wrong while implementing this change? (e.g., performance, inadvertent behavioral changes in adjacent functionality, existing tech debt, etc)
  • Care must be taken to add and remove AbortSignal listeners to avoid memory leaks
  • Signal code should be written in a way that makes it no-op when a signal is not provided (optional chaining etc) for performance
• Is there an opportunity for better cross-driver alignment or testing in this area?
  • No
• Is there an opportunity to improve existing documentation on this subject?
  • Not existing, we should document how signals can be used with the APIs we add support to

Acceptance Criteria

Implementation Requirements

• Add AbortSignal support to the TBD APIs
  • (list here)
• Ensure signal interrupts a query during any point in its lifecycle:
  • Server Selection
  • Connection Checkout
  • (if enabled) Client Side Encryption
  • R/W Socket

Testing Requirements

• Check various signal states, already aborted, aborted while the driver is in one of the lifecycle states listed above, aborted after.
• For cursor operations check abort works as expected in between commands (ex. before/after find and getMores accordingly)

Documentation Requirements

• Add API documentation to the signal option

Follow Up Requirements

• See also https://www.mongodb.com/community/forums/t/how-do-i-cancel-a-running-query/198548