JS: Library possibly removes a consumer when it should not #776
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bug
Confirmed reproducible bug
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I would propose that magic subscribe be limited to ephemerals. Durables are important contract for applications that need to be explicitly created and lifecycled. |
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I think someone should take a stab of documenting the overall behavior of subscribe in a adr :) |
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Do you recommend any work arounds? Running into this issue after converting old QueueSubscribe durable STAN Channel to a corresponding JetStream durable QueueSubscribe. |
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@philkuz in current nats.go client you can use |
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will try that out. Thanks @wallyqs ! |
kozlovic
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Aug 10, 2021
- Some refactoring to prevent lock inversion (no connection publish should be done under the subscription lock). - Remove used of jsSub mutex since so far everything can be done under the protection of the subscription's lock. - Attempt to delete JS consumer on Unsubscribe *only* if the library called AddConsumer and got a success. Resolves #775 Resolves #776 Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
kozlovic
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Aug 15, 2021
They will be described in the release notes, but gist: Added: - `DeliverSubject()` option to configure the deliver subject of a JetStream consumer created by the `js.Subscribe()` call (and variants) - `BindDeliverSubject()` option to subscribe directly to a JetStream consumer deliver subject (bypassing any lookup or JetStream consumer creation) - Fields `DeliverGroup` in `ConsumerConfig`, `PushBound` in `ConsumerInfo`. They help making prevent incorrect subscriptions to JetStream consumers - Field `Last` in `SequencePair` Changed: - With a `PullSubscription`, calling `NextMsg()` or `NextMsgWithContext()` will now return `ErrTypeSubscription`. You must use the `Fetch()` API - If the library created internally a JetStream consumer, the consumer will be deleted on `Unsubscribe()` or when the `Drain()` completes - Fail multiple instances of a subscription on the same durable push consumer (only one active at a time). Also, consumers now have the concept of `DeliverGroup`, which is the queue group name they are created for. Only queue member from the same group can attach to this consumer, and a non queue subscription cannot attach to it. Note that this requires server v2.3.5 - Attempting to create a queue subscription with a consumer configuration that has idle heartbeats and/or flow control will now result in an error Fixed: - Possible lock inversion - JetStream consumers could be incorrectly deleted on subscription's `Unsubscribe()` Resolves #785 Resolves #776 Resolves #775 Resolves #748 Resolves #747 Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
kozlovic
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Aug 15, 2021
They will be described in the release notes, but gist: Added: - `DeliverSubject()` option to configure the deliver subject of a JetStream consumer created by the `js.Subscribe()` call (and variants) - `BindDeliverSubject()` option to subscribe directly to a JetStream consumer deliver subject (bypassing any lookup or JetStream consumer creation) - Fields `DeliverGroup` in `ConsumerConfig`, `PushBound` in `ConsumerInfo`. They help making prevent incorrect subscriptions to JetStream consumers - Field `Last` in `SequencePair` Changed: - With a `PullSubscription`, calling `NextMsg()` or `NextMsgWithContext()` will now return `ErrTypeSubscription`. You must use the `Fetch()` API - If the library created internally a JetStream consumer, the consumer will be deleted on `Unsubscribe()` or when the `Drain()` completes - Fail multiple instances of a subscription on the same durable push consumer (only one active at a time). Also, consumers now have the concept of `DeliverGroup`, which is the queue group name they are created for. Only queue member from the same group can attach to this consumer, and a non queue subscription cannot attach to it. Note that this requires server v2.3.5 - Attempting to create a queue subscription with a consumer configuration that has idle heartbeats and/or flow control will now result in an error Fixed: - Possible lock inversion - JetStream consumers could be incorrectly deleted on subscription's `Unsubscribe()` Resolves #785 Resolves #776 Resolves #775 Resolves #748 Resolves #747 Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
kozlovic
added a commit
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Aug 15, 2021
They will be described in the release notes, but gist: Added: - `DeliverSubject()` option to configure the deliver subject of a JetStream consumer created by the `js.Subscribe()` call (and variants) - `BindDeliverSubject()` option to subscribe directly to a JetStream consumer deliver subject (bypassing any lookup or JetStream consumer creation) - Fields `DeliverGroup` in `ConsumerConfig`, `PushBound` in `ConsumerInfo`. They help making prevent incorrect subscriptions to JetStream consumers - Field `Last` in `SequencePair` Changed: - With a `PullSubscription`, calling `NextMsg()` or `NextMsgWithContext()` will now return `ErrTypeSubscription`. You must use the `Fetch()` API - If the library created internally a JetStream consumer, the consumer will be deleted on `Unsubscribe()` or when the `Drain()` completes - Fail multiple instances of a subscription on the same durable push consumer (only one active at a time). Also, consumers now have the concept of `DeliverGroup`, which is the queue group name they are created for. Only queue member from the same group can attach to this consumer, and a non queue subscription cannot attach to it. Note that this requires server v2.3.5 - Attempting to create a queue subscription with a consumer configuration that has idle heartbeats and/or flow control will now result in an error Fixed: - Possible lock inversion - JetStream consumers could be incorrectly deleted on subscription's `Unsubscribe()` Resolves #785 Resolves #776 Resolves #775 Resolves #748 Resolves #747 Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
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I think it is dangerous to delete (js.DeleteConsumer) a consumer when user calls sub.Unsubscribe(). Users may be used to call this function as a good practice when being done with a subscription.
The issue here is that if a user subscribes to a consumer that it does not "own" (meaning that the library did not create it), then Unsubscribe() will delete it:
nats.go/js.go
Line 928 in c7fc3c7
I believe that the library should ONLY delete JS consumer if it has created it for an ephemeral consumer (called AddConsumer inside js.subscribe()) and that there is a guarantee that no other subscription is using it (so not queue sub, or when AddConsumer returned an error meaning that someone else called AddConsumer()).
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