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https://issues.apache.org/jira/browse/BOOKKEEPER-252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450721#comment-13450721
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Ivan Kelly commented on BOOKKEEPER-252:
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I still don't like this SubscriptionChannelListener, or rather I don't like
passing it to the subscribe call at least. It adds to the main subscription API
and exposes the connection logic to the client in a way which has been nicely
hidden up until now. Moreover, I don't think it's necessary. We have a flag in
the SubscriptionOptions with this change, forceAttach, which on disconnect, the
client can check on channelDisconnect to decide whether to reconnect or not.
If you explicitly need notification at the application level, this is a
different matter, and I think it should be separate to the reconnect logic. I
think it highlights a shortcoming in the api. Currently, there is no means of
notifying a client when a the service goes down, though we haven't needed it
yet. However, if this is a requirement for your usecase, we should go about
solving it, but without exposing the underlying connection.
> Hedwig: provide a subscription mode to kill other subscription channel when
> hedwig client is used as a proxy-style server.
> --------------------------------------------------------------------------------------------------------------------------
>
> Key: BOOKKEEPER-252
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-252
> Project: Bookkeeper
> Issue Type: New Feature
> Affects Versions: 4.1.0
> Reporter: Sijie Guo
> Assignee: Sijie Guo
> Fix For: 4.2.0
>
> Attachments: BK-252.diff, BOOKKEEPER-252.diff, BOOKKEEPER-252.diff
>
>
> In some case, we need to hedwig-client as proxy server to provide messaging
> service to other users.
> client -> proxy server 1 -> hedwig
> \> proxy server 2 />
> when client would connect to either proxy server to receive messages, the
> proxy server would setup subscription channel to hedwig server.
> we just want client to be simple, so when the channel between client and
> proxy server is broken, client will try to connect to proxy servers thru VIP.
> it might connect to other proxy server. for example, first time client
> connects to proxy server 1, but the client found the connection is broken, it
> connects to proxy server 2. when proxy server 2 tried to setup subscription
> channel to hedwig, hedwig found that this subscription has existed before
> occupied by proxy server 1.
> the panic here is that proxy server 1 only disconnect old subscription
> channel only when it detected the channel between client and itself is
> broken. The detection might be delayed due to several reasons. so it might
> increment the latency that messages are pushed to real client.
> so we try to introduce a subscription mode called CREATE_OR_ATTACH_OR_KILL
> mode.
> when a subscriber use this subscription mode, it would kill old existed
> subscription channel. when using this subscription mode, we would turn off
> auto-reconnect functionality in hedwig client and just tell client about the
> channel disconnected event so client could do its logic when channel is
> detected.
> in order to provide some admin tool for admin guys to debug/operate, we
> provide ADMIN mode. if a subscriber attach to a subscription using ADMIN
> mode, its subscription channel would never be killed, then it is safe to
> guarantee admin operations.
>
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