Hi, Yubiao
I agree with this idea because some users care about the production rate. They
don't want to unload the whole topic to fix the subscription problem.
I've got some questions:
1. How do you handle the race condition when you are trying to unload the
subscription, and the new consumer wants to subscribe to this subscription at
the same time? I'm unsure if it has the race condition. I just want to remind
you about that. :)
2. Would you like to add some restful API design to clarify the implementation?
a. Request method
b. Request path
c. Response code
d. etc.
Thanks for your work.
Mattison
On Jan 11, 2023, 17:01 +0800, Yubiao Feng
<yubiao.f...@streamnative.io.invalid>, wrote:
> Hi community
>
> I am starting a DISCUSS for PIP-240: A new API to unload subscriptions.
>
> PIP issue: https://github.com/apache/pulsar/issues/19187
>
> ### Motivation
>
> We sometimes try to unload the topic to resolve some consumption-stop
> issues. But the unloading topic will also impact the producer side.
>
> ### Goal
>
> Providing a new API to unload the subscription dimension triggers
> reconnection of all consumers on that subscription and reconnection is
> guaranteed by the client. The API will be used in these ways:
> - unload special subscription of one topic(or partitioned topic)
> - unload all subscriptions of one topic(or partitioned topic)
> - unload subscriptions of one topic(or partitioned topic) by regular
> expression
> - If a reader's subscription name is not set, a random subscription name
> prefixed with 'multiTopicsReader-' or 'reader-' will be used, and users can
> uninstall these subscriptions using regular expressions.
>
> In addition to triggering consumer disconnection, Unloading Subscribers
> will restart the Dispatcher, which resets the redeliver message queue and
> delayed message queue in the Broker's memory, which can help resolve issues
> caused by an abnormal dispatcher state. However, the execution flow of
> Unloading Subscribers does not include a restart of the Managed Cursor
> related to this dispatcher; if there is a problem with the cursor, we can
> only rely on the unload topic to solve it.
>
> Note: From the client's perspective, this connection may be shared by
> consumers, producers, and transactions, so Unloading Subscribers maybe
> impact the producer and transaction.
>
> #### These scenarios are not supported
> - Functions `message-dedup`, `geo-replication,` and `shadow-topic` also
> read messages from the topic, but Unloading subscribers will not support
> triggering restarts of these three functions( because the cursor is used
> directly to read the data in these scenarios, not the consumer or reader ).
> - The Compression task(subscription name is `__compaction`) also use a
> reader to read data, but Unloading Subscribers does not support it because
> this task creates a new reader each time it starts.
> - Do not support all topics related to Transaction features.
> - `__transaction_buffer_snapshot` works with the task TB recover, and
> this task will create a new reader each time they start.
> - `__transaction_pending_ack` works with the task Transaction Pending Ack
> Store replay, and this task will use managed cursor directly to read data.
> - `__transaction_log_xxx` works with the task Transaction Log, which will
> use managed cursor directly to read data.
> - `transaction_coordinator_assign` No data will be written on this topic.
>
> #### Special system topic supports
> The system topic `__change_events` is used to support topic-level policies,
> there may also be some message delivery issues in this scenario, so
> Unloading Subscribers will support this topic.
>
> ### API Changes
>
> #### For persistent topic
> ```
> pulsar-admin persistent unload {topic_name} -s {sub_name}
> ```
>
> #### For non-persistent topic
> ```
> pulsar-admin non-persistent unload {topic_name} -s {sub_name}
> ```
>
> #### Explain the param `-s`
> - set param `-s` to special sub name to unload special subscription
> - set param `-s` to `**` to unload all subscriptions under this topic
> - set param `-s` to `regexp` to unload a batch subscriptions under this
> topic
>
>
> Thanks
> Yubiao Feng
