[jira] [Commented] (CASSANDRA-16484) Audit consumption/removal of ApplicationState padding

["Brandon Williams (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-16484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17295314#comment-17295314 ] 

Brandon Williams commented on CASSANDRA-16484:
----------------------------------------------

First, some explanation.  Since AS uses an enum, if a state outside of that is referenced, the enum is blown and the gossiper is toast.  This is unfixable without downtime since the now poisonous state is in the 'gossip ether.'  This is why X_11_PADDING exists in a special position, because we nearly made what I call 'gossipocalypse' happen around that timeframe, by adding too many states.  The other padding states were added about the same time, as a preventative measure for the future.  This is so that the enum has room for new states in a newer version that can be accessed without blowing the enum in lesser versions (even though the states are just padding to those machines, and thus useless.)

These are not intended to be consumed, as that would put a nonsensical limit on how many states we can ever add, where the intent is that the padding creates enough room to add the same amount of new states between versions.  Thus, new states should always be added, before the padding, and the padding left untouched so that the next version also has room to perform addition safely.

> Audit consumption/removal of ApplicationState padding
> -----------------------------------------------------
>
>                 Key: CASSANDRA-16484
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16484
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Cluster/Gossip
>            Reporter: Brandon Williams
>            Assignee: Brandon Williams
>            Priority: Normal
>             Fix For: 4.0-beta
>
>
> It looks like some padding states, which should never be removed or changed, has occurred in ApplicationState.  This ticket will serve to correct that.



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