On Thu, Sep 8, 2011 at 03:12, Joseph Blomstedt <j...@basho.com> wrote:
> Given that 1.0 prerelease packages are now available, I wanted to
> mention some changes to Riak's clustering capabilities in 1.0. In
> particular, there are some subtle semantic differences in the
> riak-admin commands. More complete docs will be updated in the near
> future, but I hope a quick email suffices for now.
>
> [nodeB/riak-admin join nodeA] is now strictly one-way. It joins nodeB
> to the cluster that nodeA is a member of. This is semantically
> different than pre-1.0 Riak in which join essentially joined clusters
> together rather than joined a node to a cluster. As part of this
> change, the joining node (nodeB in this case) must be a singleton
> (1-node) cluster.
>
> In pre-1.0, leave and remove were essentially the same operation, with
> leave just being an alias for 'remove this-node'. This has changed.
> Leave and remove are now very different operations.
>
> [nodeB/riak-admin leave] is the only safe way to have a node leave the
> cluster, and it must be executed by the node that you want to remove.
> In this case, nodeB will start leaving the cluster, and will not leave
> the cluster until after it has handed off all its data. Even if nodeB
> is restarted (crashed/shutdown/whatever), it will remain in the leave
> state and continue handing off partitions until done. After handoff,
> it will leave the cluster, and eventually shutdown.
>
> [nodeA/riak-admin remove nodeB] immediately removes nodeB from the
> cluster, without handing off its data. All replicas held by nodeB are
> therefore lost, and will need to be re-generated through read-repair.
> Use this command carefully. It's intended for nodes that are
> permanently unrecoverable and therefore for which handoff doesn't make
> sense. By the final 1.0 release, this command may be renamed
> "force-remove" just to make the distinction clear.
>
> There are now two new commands that provide additional insight into
> the cluster. [riak-admin member_status] and [riak-admin ring_status].
>
> Underneath, the clustering protocol has been mostly re-written. The
> new approach has the following advantages:
> 1. It is no longer necessary to wait on [riak-admin ringready] in
> between adding/removing nodes from the cluster, and adding/removing is
> also much more sound/graceful. Starting up 16 nodes and issuing
> [nodeX: riak-admin join node1] for X=1:16 should just work.
>
> 2. Data is first transferred to new partition owners before handing
> over partition ownership. This change fixes numerous bugs, such as
> 404s/not_founds during ownership changes. The Ring/Pending columns in
> [riak-admin member_status] visualize this at a high-level, and the
> full transfer status in [riak-admin ring_status] provide additional
> insight.
>
> 3. All partition ownership decisions are now made by a single node in
> the cluster (the claimant). Any node can be the claimant, and the duty
> is automatically taken over if the previous claimant is removed from
> the cluster. [riak-admin member_status] will list the current
> claimant.
>
> 4. Handoff related to ownership changes can now occur under load;
> hinted handoff still only occurs when a vnode is inactive. This change
> allows a cluster to scale up/down under load, although this needs to
> be further benchmarked and tuned before 1.0.
>
> To support all of the above, a new limitation has been introduced.
> Cluster changes (member addition/removal, ring rebalance, etc) can
> only occur when all nodes are up and reachable. [riak-admin
> ring_status] will complain when this is not the case. If a node is
> down, you must issue [riak-admin down <node>] to mark the node as
> down, and the remaining nodes will then proceed to converge as usual.
> Once the down node comes back online, it will automatically
> re-integrate into the cluster. However, there is nothing preventing
> client requests being served by a down node before it re-integrates.
> Before issuing [down <node>], make sure to update your load balancers
> / connection pools to not include this node. Future releases of Riak
> may make offlining a node an automatic operation, but it's a
> user-initiated action in 1.0.
>
> -Joe
Hello!
I'm quite happy to see that things related to clustering have been
worked on, so "Nice work!". :)
My guess is that all this went actually in the Riak-Core
repository (I haven't looked over the repository). Thus -- as I'm a
user of Riak-Core -- what else notable has changed in Riak-Core.
Thanks,
Ciprian.
_______________________________________________
riak-users mailing list
riak-users@lists.basho.com
http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
