We do support rolling upgrade. And further, we also support the following scenario:
1) Run a cluster, using a cache store that is *not* shared. Entries get hashed to
specific nodes.
2) Shut down the cluster, upgrade Infinispan.
3) Should still be able to locate your entries, as they would be loaded from the cache
stores.
If the hash function changes between upgrades, then requests for keys would now be mapped
to different nodes, and the keys won't be found in those nodes' cache stores.
On 14 Jan 2011, at 09:45, Sanne Grinovero wrote:
I'm wondering why you're considering backwards compatibility
of the
hashing distribution. Is Infinispan supposed to support multiple
different versions to be connected in a cluster, providing some form
of rolling upgrade?
Cheers,
Sanne
2011/1/14 Emmanuel Bernard <emmanuel(a)hibernate.org>:
> Or release a 4.3.
>
> On 14 janv. 2011, at 09:32, Bela Ban wrote:
>
>> I would fix the existing MurmurHash; IMO backward compat doesn't extend
>> to consistent hashing...
>>
>> Does leaving the 1 bit out create extreme anomalies wrt hashing
>> distribution ? I wouldn't think so...
>>
>> I'm fine with the other solution, too.
>>
>>
>>
>> On 1/13/11 8:35 PM, Manik Surtani wrote:
>>> Guys,
>>>
>>> The MurmurHash2 impl we have in 4.2.0 is buggy in that my translation from
the original C source was faulty and it effectively hashes over just 31 bits instead of
32. It means the distribution result isn't as good as it could be.
>>>
>>> Now it isn't that easy for me to just *fix* this in 4.2.1, since it means
keys mapped to nodes using 4.2.0 may not map to the same node in 4.2.1.
>>>
>>> So here is what I propose:
>>>
>>> 1) Fix it in 4.2.x as MurmurHash2A
>>> 2) Use MurmurHash2A by default, *unless* a config flag is provided that
forces the use of MurmurHash2. (e.g.,<hash function="MurmurHash2">)
>>>
>>> This will even give us the ability to use MurmurHash3 in 5.0 when we have
it.
>>>
>>> WDYT?
>>
>>
>> --
>> Bela Ban
>> Lead JGroups / Clustering Team
>> JBoss
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>>
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>
>
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--
Manik Surtani
manik(a)jboss.org
twitter.com/maniksurtani
Lead, Infinispan
http://www.infinispan.org