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From "paul cannon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4480) Binary protocol: adds events push
Date Wed, 05 Sep 2012 06:11:08 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448511#comment-13448511
] 

paul cannon commented on CASSANDRA-4480:
----------------------------------------

I don't think Jonathan cares much, and although I still don't like the mode separation, I'd
rather have this committed sooner than later, and I don't want to take up your time, so let's
just go with it.

So the other minor things I've seen with this patch are:

 * The doc implies that the "status_change", "topology_change", "new_node", "up", etc strings
are lowercase, but they're sent in uppercase. We should probably document that the case could
be upper, or that they could be in either case, or change to sending lowercase.
 * In my tests using ccm (with a subsequent ccm add), the STATUS_CHANGE - UP event notification
appears to be sent twice. Probably it doesn't matter for any practical purpose, but I mention
it in case it's indicative of a bug.
 * This probably isn't isolated to this change, but I noticed it here: when something results
in an error message on the native protocol, the resulting error message does not have a matching
stream-id for the corresponding request. Makes it hard to send back to the right place.
                
> 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
>
>         Attachments: 4480.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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