----- "Manik Surtani" <manik(a)jboss.org> wrote:
On 21 Apr 2010, at 12:10, Galder Zamarreno wrote:
> 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?
4.1 is fine. Also, I presume by getPosition() you really mean
getHashId(), which will be between 0 and HASH_SPACE (as opposed to a
relative position meaning, before AddressX and after AddressY)?
Indeed I meant that. The hash position or id, I'll go with getHashId().
> 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?
Well, we *could* maintain this order, but I don't think it should be
mandated since order can easily be regained by sorting on the hash
ids.
Sure, it could always be ordered. I assumed that the client would need to do some ordering
after applying the hash on a key and trying to decide which server to send invocation too.
Hence, my idea of giving the list ordered to the client would be to make their life
easier.
Then again, while implementing detection of crashed members in Hot Rod to update the Hot
Rod topology information, I found that not providing order guarantees could make the
internals more flexible. For example, we could maintain this topology as a map rather than
a list, hence making more efficient to discover whether a member has crashed or not. The
efficiency improvement comes from the fact that I checked for crashed members by listening
to JGroups view changes and when new member list is smaller than the new one, checking
whether any of the nodes that is no longer part of the view is still present in the Hot
Rod topology list. Hence, this requires traversing the list which is O(n).
So, to summarise, I prefer not to mandate any order for the time being.
>
> Cheers,
>
> ----- "Manik Surtani" <manik(a)jboss.org> wrote:
>
>> On 19 Apr 2010, at 10:58, galder(a)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_Clie...
>> - 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(a)lists.jboss.org
>>>
https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>
>> --
>> Manik Surtani
>> manik(a)jboss.org
>> Lead, Infinispan
>> Lead, JBoss Cache
>>
http://www.infinispan.org
>>
http://www.jbosscache.org
>>
>>
>>
>>
>>
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>
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--
Manik Surtani
manik(a)jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org
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