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https://issues.apache.org/jira/browse/ZOOKEEPER-2879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16136823#comment-16136823
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Dan Benediktson commented on ZOOKEEPER-2879:
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[~hanm] No, local sessions are not a sufficient mitigation for the problems
introduced by this proposed feature:
- Local sessions can be upgraded to a global session at any time by creating an
ephemeral node; basically, enabling local sessions across an ensemble does not
guarantee that all sessions are local. If one of them upgrades, for instance,
what happens to the other one?
- Moreover, I believe this proposed feature would let you accidentally reuse a
local session across two members of the same ensemble. Imagine two sessions
connect to different members and get the same session ID: now, one of them
disconnects and tries to reconnect, and lands on the second server (this is
possible: local sessions are purely a server-side concept, so in practice
clients with a local session DO try to reconnect to another server, even though
it is guaranteed to fail). I expect it would succeed, at which point there are
would be two connections for the same local session, one of which actually
originated from another node. I don't know precisely what this would entail,
but it's probably also undesirable.
> Adding observers dynamically without server id
> ----------------------------------------------
>
> Key: ZOOKEEPER-2879
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2879
> Project: ZooKeeper
> Issue Type: Improvement
> Components: quorum
> Affects Versions: 3.6.0
> Reporter: Fangmin Lv
> Assignee: Fangmin Lv
>
> Dynamic config requires observer has unique server id, which means we cannot
> simply add observer with dynamic server id -1. For large observer cluster,
> it's much more easier to add observer without unique server id if it doesn't
> need to be promoted to participant. Also, it will make dynamic config more
> efficient, we don't need to store and send the long list of observers during
> re-config.
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