[infinispan-dev] ISPN-384 - Implementing hash distribution aware headers in Hot Rod

[Galder Zamarreno]

Ok, what about the rest of the points made? 

I.e. Adding int getPosition(Address a) to ConsistentHash interface. Can we do that in 4.1? Or do we have to wait for 5.0?

Ordering of servers in views returned: For topology changes, ordered in started order and for hash aware topology changes, servers ordered in ascending hash wheel position?

Cheers,

----- "Manik Surtani" <manik at jboss.org> wrote:

> On 19 Apr 2010, at 10:58, galder at redhat.com wrote:
> 
> > Hi,
> > 
> > Re: https://jira.jboss.org/jira/browse/ISPN-384
> > 
> > The topology headers are in, so the next step is to get the hash
> distribution headers in. The first step here is for Hot Rod servers to
> be able to query an Address' position in the wheel so that this is
> sent back to clients (This is what I refer to by hashcode in
> http://community.jboss.org/wiki/HotRodProtocol#HashDistributionAware_Client_Topology_Change_Header
> - it really is the hash wheel position). However, there's no such API
> at the  moment that allows clients to query it. Having had a look, the
> most reasonable thing would be to add something like this to the
> ConsistentHash interface:
> > 
> > int getPosition(Address a)
> > 
> > However, this might be somehow limiting if we end up implementing
> virtual nodes. ExperimentalDefaultConsistentHash hints at the
> possibility of that happening and so something like this might more
> future proof:
> > 
> > List[Integer] getPositions(Address a)
> 
> We shouldn't design for something that may not be realised.  vnodes
> are very problematic for many reasons and if we can achieve what we
> need to achieve without vnodes then that would be my preference.
> 
> > This also highlights the limitation of the Hot Rod spec where it's
> assumed that a server has a single position. 
> > 
> > Moreover, these brings up another interesting topic which is the
> order in which Hot Rod orders the servers in the headers. For topology
> headers, although not written down, I'm following the same kind of
> pattern used at the JGroups level where serves started first appear in
> first in the list returned. I should probably add this to the protocol
> wiki. 
> > 
> > In the case of hash distribution headers, I think it'd make sense
> for the order to be based on the hash wheel position in ascendant
> order. That way it would make life easier for clients to find the
> target node for the operation, since it'd avoid them having to do the
> sorting and finding out the next node. If we take this into account
> with the fact  that a node might map to multiple positions, I think
> the hash distribution header might be look better this way:
> > 
> > [Response header][Topology Id][Num Key Owners][Hash Function
> Version][Hash space size][Num servers in topology]
> > -> New: 
> > [*m1: Server Id*][m1: Host/IP length][m1: Host/IP address]
> > [*m2: Server Id*][m2: Host/IP length][m2: Host/IP address]...
> > [*m3: Server Id*][m3: Host/IP length][m3: Host/IP address]...
> > [Num total positions]
> > [*m2: Server Id*][m2: hash wheel position 1]
> > [*m3: Server Id*][m3: hash wheel position 2]
> > [*m2: Server Id*][m2: hash wheel position 2]
> > [*m3: Server Id*][m3: hash wheel position 1]
> > [*m3: Server Id*][m3: hash wheel position 3]
> > [*m1: Server Id*][m1: hash wheel position 1]
> 
> Again, this assumes > 1 position for a node.  I think we should not
> design for this at this stage.  
> > 
> > So, above I've splitted the server host/port definitions in one side
> and then the hash wheel positions. I did this to avoid repeating the
> host/port definition which each hash wheel definition. I've also added
> a number of total positions and the list following it is ordered in
> ascendant order of position. The server id would be a vInt.
> > 
> > WDYT?
> > 
> > --
> > Galder Zamarreño
> > Sr. Software Engineer
> > Infinispan, JBoss Cache
> > 
> > _______________________________________________
> > infinispan-dev mailing list
> > infinispan-dev at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/infinispan-dev
> 
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
> 
> 
> 
> 
> 
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