[GitHub] codelipenghui commented on issue #2688: Polices On Topic

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codelipenghui commented on issue #2688: Polices On Topic
URL: https://github.com/apache/pulsar/issues/2688#issuecomment-432108404
 
 
   @ivankelly 
   > 
   > This change will cause more load on zookeeper. For each topic loaded, we would have to do a read for the policy of that topic when loading the topic policy, even if no topic policy exists.
   > 
   > How does the broker get notified of updated to the policy for a topic? If we add a watcher, that's a watcher per topic. We should consider if there's another way of doing this without placing more load on ZK, such as in a 'system' topic.
   
   Yes, this is a very necessary concern. I think 'system' topic is an excellent solution. 
   
   1. For policy changed, send message to the 'system' topic and  write to zookeeper, then 'system' topic consumer update policy cache in broker. So that just need to read the cache.
   2. For topic owner changed, load the namespace policy and topic policy into broker cache.
   
   For 'system' topic design. I'm not sure the 'system' topic border.
   
   1. A 'system' topic in a cluster
   2. Namespace 'system' topic / Topic 'system' topic
   3. 'system' topic for each namespace / 'system' topic for each topic
   
   I'm prone to 1 or 2, for 3 too much topic will be created.
   
   @ivankelly Can you give me some idea more ? Thanks
   
   
   

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