On 18 Feb 2010, at 06:39, Patricio Echagüe wrote:

> Hi, I have written a Cassandra Persistence Manager but as Jukka mentioned,
> there are some issues to resolve.
> The other problem I see is that Cassandra does not support transaction
> across multiple keys.

I havent looked at the PM yet, but have been doing a JGroups based 
ClusterNode/Journal as a start, was not intending to put the Journal in 
Cassandra (that might be a mistake)

Remind me, 
Is the problem that Cassandra might not take multiple key updates to Bundle, 
Binval and Refs atomically or that its not possible to have the "transaction 
monitor" inside the PM. IIRC the PM is a form of transaction monitor ?

Also, (potentially dumb question), could you merge Bundle, Binval and Refs ? 
(or would that just kill performance)
Ian



> The JR PM assumes that the change logs are saved all or none of them. That
> represents another issue. (I assume a bundle approach)
> 
> Just to keep the discussion, this is my Keyspace
> 
>  <Keyspaces>
>   <Keyspace Name="myCassandraPM">
> 
>      <ColumnFamily CompareWith="BytesType" Name="WORKSPACE_Bundle" />
>      <ColumnFamily CompareWith="BytesType" Name="WORKSPACE_Binval" />
>      <ColumnFamily CompareWith="BytesType" Name="WORKSPACE_Refs" />
> 
>      <ColumnFamily CompareWith="BytesType" Name="VERSION_Bundle" />
>      <ColumnFamily CompareWith="BytesType" Name="VERSION_Binval" />
>      <ColumnFamily CompareWith="BytesType" Name="VERSION_Refs" />
> 
>      <ColumnFamily CompareWith="BytesType" Name="SECURITY_Bundle" />
>      <ColumnFamily CompareWith="BytesType" Name="SECURITY_Binval" />
>      <ColumnFamily CompareWith="BytesType" Name="SECURITY_Refs" />
> 
>    </Keyspace>
>  </Keyspaces>
> 
> Patricio
> 
> On Wed, Feb 17, 2010 at 6:47 AM, Ian Boston <i...@tfd.co.uk> wrote:
> 
>> 
>> On 17 Feb 2010, at 14:34, Jukka Zitting wrote:
>> 
>>> Hi,
>>> 
>>> On Wed, Feb 17, 2010 at 11:53 AM, Ian Boston <i...@tfd.co.uk> wrote:
>>>> On 17 Feb 2010, at 10:43, Jukka Zitting wrote:
>>>>> I'm not aware of anything like that, though there's been some
>>>>> discussion about persistence on top of distributed databases or hash
>>>>> tables. The main problem with such approaches is the eventual
>>>>> consistency model that can be troublesome for the current Jackrabbit
>>>>> architecture.
>>>> 
>>>> Is that because, in a cluster one JR node might get an event that an
>>>> Item exists, but its not yet present on the backend its connected to,
>>>> and there are no guarantees over the order in which items appear,
>>>> so, for instance, the hierarchy manager might find a child but not
>>>> the parent?
>>> 
>>> Exactly. The current Jackrabbit architecture assumes that the
>>> underlying persistence store is always (not just eventually)
>>> consistent.
>> 
>> 
>> Ok, I'm looking into ways to address that. The other one, I suspect is
>> going to be the sequence ID on the journal event stream, which IIRC needs to
>> be sequential so the journal can be replayed, also since the biggest source
>> of eventually consistent errors is going to be that journal stream I am
>> thinking binding the journal with the PM might allow remote nodes to know
>> when a local item is out of date, if an item in the local PM is stale, and
>> which server to get the latest item copy from. That assumes nothing changes
>> without a journal record being emitted. I want to avoid sending the journal
>> via storage.
>> 
>>> 
>>>> Do you have any pointers to the discussions so I can go and read ?
>>> 
>>> It's been mostly coffee room discussions so far, but I'll bring up the
>>> topic soon on dev@ as a part of a larger Jackrabbit 3 roadmap
>>> discussion.
>> 
>> I commented on you JR3 rfi, but I am still thinking about JR2
>> 
>>> 
>>> BR,
>>> 
>>> Jukka Zitting
>> 
>> 
> 
> 
> -- 
> Patricio.-

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