[erlang-questions] gen_leader and adding candidates at runtime

Ulf Wiger (TN/EAB) <>
Thu Dec 14 19:02:35 CET 2006


It isn't impossible - it's just difficult. (:

You can add candidates through a code change.
That's the only time when the callback module 
is allowed to do whatever it wants to the 
leader election record.

The reason behind the restriction is that the 
leader election algorithm depends on the candidate
lists on all nodes being identical. It esp. mustn't 
change during the election process. (*)

During code change, not only is it a reasonable 
and common restriction that all nodes must be available.
There is also normally a fallback in place for the 
case that something goes wrong during the upgrade.

(*) At least that was true with the first algorithm.
    I'm guessing that it's true for the new one as well.

This can of course be improved, but it's not a trivial
problem. Contributions are welcome.  (:

BR,
Ulf W

> -----Original Message-----
> From:  
> [mailto:] On Behalf Of t ty
> Sent: den 14 december 2006 17:39
> To: 
> Subject: [erlang-questions] gen_leader and adding candidates 
> at runtime
> 
> Hello,
> 
> It is currently impossible to add new candidates at runtime. 
> What is the reason behind this restriction ?
> 
> Thanks
> 
> t
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