[infinispan-dev] Proposal: ISPN-1394 Manual rehashing in 5.2

[Mircea Markus]

> We could extend the policy for craches as well, by adding a
> minNumOwners setting and only triggering an automatic rehash when
> there is a segment on the hash wheel with <= minNumOwners owners.

minNumOwners should be at least 1, which in the default use case (numOwners==2) would mean that we react to every leave.
Whilst this functinality is very nice, I don't think it should have a high prio as most of the use cases I'm aware of use numOwners=2.
> 
> We would have a properly installed CH, that guarantees at some point
> in the past each key had numOwners owners, and a filter on top of it
> that removes any leavers from the result of DM.locate(),
> DM.getPrimaryLocation() etc.
> 
> It would probably undo our recent optimizations around locate and
> getPrimaryLocation, so it's slowing the normal case (without any
> leavers) in order to make the exceptional case (organized shutdown or
> a part of the cluster) faster.
> The question is how big the cluster
> has
> to get before the exceptional case becomes common enough that it's
> worth optimizing for...
re:partial shutdown, due to consistency constraints, it won't be posible to controlled shutdow more than numOwners-1 nodes at any time, so not sure it this optimisation has a broad scope.
For total shutdown, I guess we can use other means that rehash, e.g. a specific command that would disable it and start flushing to the store.