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From "Brandon Williams (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4480) Binary protocol: adds events push
Date Fri, 07 Sep 2012 15:06:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450689#comment-13450689
] 

Brandon Williams commented on CASSANDRA-4480:
---------------------------------------------

onAlive and onDead are basically relaying FD information, as in the node is known but has
died or come back, whereas onJoin/onRestart indicate the node is new (but not necessarily
a member) or rebooted (generation changed), which is where your problem is (but onJoin _and_
onRestart fire for that case.)  onRemove means the node has left, by decom/removetoken/assassinate.
 But you'll want to ask tMD if the node is a member in any case, otherwise your events will
fire for fat clients, like bootstrapping nodes that haven't fully joined yet.
                
> Binary protocol: adds events push 
> ----------------------------------
>
>                 Key: CASSANDRA-4480
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4480
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>             Fix For: 1.2.0 beta 1
>
>         Attachments: 4480.txt, 4480-v2.txt
>
>
> Clients needs to know about a number of cluster changes (new/removed nodes typically)
to function properly. With the binary protocol we could start pushing such events to the clients
directly.
> The basic idea would be that a client would register to a number of events and would
then receive notifications when those happened. I could at least the following events be useful
to clients:
> * Addition and removal of nodes
> * Schema changes (otherwise clients would have to pull schema all the time to know that
say a new column has been added)
> * node up/dow events (down events might not be too useful, but up events could be helpful).
> The main problem I can see with that is that we want to make it clear that clients are
supposed to register for events on only one or two of their connections (total, not per-host),
otherwise it'll be just flooding. One solution to make it much more unlikely that this happen
could be to distinguish two kinds of connections: Data and Control (could just a simple flag
with the startup message for instance). Data connections would not allow registering to events
and Control ones would allow it but wouldn't allow queries. I.e. clients would have to dedicate
a connection to those events, but that's likely the only sane way to do it anyway.

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