Re: using virtual synchrony for CTDB

[Tracy Camp]

> The DMASTER/LMASTER concept is all about resource masters and resource
> affinity. The common case for a file server is not have much contention
> (take for example a server sharing home directories), and lock
> contention is always expensive, no matter what you do.
> What we want to achieve is to not pay the cost of a system engineered
> against locking contention at the expenses of operations where you don't
> have it.

Yup.  The point is that you can't scale write workloads within whatever 
the locking granularity is by spreading them across more systems.  You 
_can_ scale read workloads however.  So you design your cluster for that. 
The CTDB proposal appears to do just that.

Something about the DMASTER redirect is bothering me though.  Wouldn't it 
be possible to build up 'harmonics' in the cluster since there doesn't 
appear to be any terminating condition for redirects?  I've seen things 
like this happen.  Might be better to have a redirect limit of 1 hop or 
something like that and then require a return to the LMASTER.

Tracy Camp

> Simo.