[GitHub] [helix] pkuwm commented on pull request #1066: Prevent parallel controller pipelines run causing two master replicas

[GitBox <gi...@apache.org>]

pkuwm commented on pull request #1066:
URL: https://github.com/apache/helix/pull/1066#issuecomment-668990390


   > A high level question. The following approach basically encode the session info to the data of ZkClient? Last time in the design discussion I guess people raised the concern that this mean ZkClient need to understand the data format. Normally lower level do not understand higher level data.
   > 
   > Though you can also think of session id in the data as meta data, just like TCP has out of line control data.
   > 
   > Either way is fine to me. Just want to make sure @pkuwm and @lei-xia agree with this approach.
   > 
   > ```
   >   private String parseExpectedSessionId(Object data) {
   >     if (!(data instanceof SessionAwareZkWriteData)) {
   >       return null;
   >     }
   >     return ((SessionAwareZkWriteData) data).getExpectedSessionId();
   > ```
   
   We add a new interface SessionAwareZkWriteData to make it generic: representing data is session aware. In future, we may implement this interface to have a public one like SessionAwareZNRecord . With this new interface, ZkClient doesn’t need to change: treating SessionAwareZkWriteData as generic one. 
   
   How about this? @lei-xia @jiajunwang @kaisun2000 
   Considering the new interface would tie session to zk, it is not generic enough. Eg. if we change the storage to mysql, it doesn’t have session.
   How about this, splitting the PR into 2: 1st one (this one) doesn’t have new interface, 2nd one will have the new interface. If we don’t agree on adding new interface, we just discard the 2nd PR, being tracked in https://github.com/apache/helix/issues/1219.


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