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Type:
Bug
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: 3.3.2
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Component/s: None
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Environment:Ubuntu 18.04.3 LTS
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I have been monitoring a peek-a-boo issue on servers that are relying on `db.watch` API. After an arbitrary period of time the `changeStream` will stop receiving events and none of the following events are fired [ever]:
const changeStream = db.watch() ... changeStream.on('error', event => ...) changeStream.on('end', event => ...) changeStream.on('close', event => ...)
Until recently, I did not have any logs to correlate the reason for the changeStream to stop receiving events so I attempted a band-aid fix arbitrary "disconnects" with:
setInterval(() => {
if (changeStream.isClosed())
throw new Error('changeStream is closed')
}, 60000)
When the changeStream has stopped receiving events, the above interval call to changeStream.isClosed() is still returning false (thinking the changeStream is still open).
I discovered (through the help of Sentry error logging) that another server (API web-service) has received this error roughly at the time of the last event received on the above changeStream:
MongoTimeoutError: Server selection timed out after 30000 ms File "/srv/ws-core/node_modules/mongodb/lib/core/sdam/topology.js", line 798, col 7, in selectServers new MongoTimeoutError(`Server selection timed out after ${timeout} ms`), File "/srv/ws-core/node_modules/mongodb/lib/core/sdam/topology.js", line 872, col 7, in NativeTopology.descriptionChangedHandler selectServers(topology, selector, timeout, start, callback); File "events.js", line 277, col 13, in Object.onceWrapper File "events.js", line 194, col 15, in NativeTopology.emit File "domain.js", line 441, col 20, in NativeTopology.EventEmitter.emit File "/srv/ws-core/node_modules/mongodb/lib/core/sdam/topology.js", line 524, col 10, in NativeTopology.serverUpdateHandler this.emit( File "events.js", line 189, col 13, in Server.emit File "domain.js", line 441, col 20, in Server.EventEmitter.emit File "/srv/ws-core/node_modules/mongodb/lib/core/sdam/monitoring.js", line 182, col 12, in successHandler server.emit('descriptionReceived', new ServerDescription(server.description.address, isMaster)); File "/srv/ws-core/node_modules/mongodb/lib/core/sdam/monitoring.js", line 195, col 7, in checkServer successHandler(isMaster);
Because of the business critical logic, this stoppage in changeStream events is recognized within a few hours triggering investigation into why - it has always resulted in the requirement to restart the Node.js app that is creating the changeStream.
Expected Behavior
- I expect an event (`error`, `close`, `timeout`, etc) to be fired when a changeStream is no longer "connected".
- I expect `changeStream.isClosed()` to be accurate every time it is called.