Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-06 Thread Andreas Jung
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Aran Dunkley wrote:
> Hi guys,
> 
> It's looking like Plone/ZODB would need too much modification and
> testing at the current time to move in to P2P.

Neither Plone nor ZODB require modifications. You need a cloud-aware
storage suitable to be used as ZODB storage.

- -aj
> 
> The most promising environment in our research so far are frameworks
> built on the Squeak language which is used by the OpenCobalt project (a
> P2P collaborative 3D world).
> 
> Thanks for all your feedback and advice, and happy new year :-)
> Aran
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-06 Thread Aran Dunkley
Hi guys,

It's looking like Plone/ZODB would need too much modification and
testing at the current time to move in to P2P.

The most promising environment in our research so far are frameworks
built on the Squeak language which is used by the OpenCobalt project (a
P2P collaborative 3D world).

Thanks for all your feedback and advice, and happy new year :-)
Aran
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-06 Thread Shane Hathaway
On 01/03/2011 10:23 PM, Aran Dunkley wrote:
> Hi, I'm part of a development team who are helping an organisation to
> architect a CMS based project that they want to work in a P2P network
> rather than using a centralised web-server. We'd prefer to use an
> existing popular CMS as a starting point so that it is mature, has a
> large development community and a wide range of extensions/modules
> available.
>
>> From our initial research it seems that Plone should be more capable of
> moving in to the P2P space due to it using ZODB rather than SQL and that
> ZODB seems able to be connected to a variety of storage mechanisms. I'm
> wondering what you guys, the core developers, think of the
> practicalities of Plone in P2P, for example could ZODB use a DHT as its
> storage layer? what kind of querying is required on the DHT?
>
> We have a good budget available for this and will be developing it as a
> completely free open source component, so we'd also like to hear from
> developers who may be interested in working on the project too.

I think you're right that you can think of ZODB as little more than a 
transactional key-value store.  It would be very cool to find a way to 
implement a DHT-based ZODB storage, but here is your challenge:

1. Each ZODB thread has its own cache of objects.  Each cache must be 
invalidated appropriately.  This cache is the key to ZODB speed, but 
historically, it has also been a major source of bugs.

2. The BTrees used in catalogs are very sensitive to consistency 
violations, so unless you are going to redesign the catalog, there is no 
room for error in transactional consistency.

3. MVCC support is required, meaning that database reads must see old 
data, not see newly committed data, until transaction boundaries.

4. Also due to the catalog, latency is a major concern.  It is not 
uncommon for a catalog request to read the state of 10,000 objects or 
more, and you don't want that request to take more than a few seconds. 
Memcached can help here.

Shane
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-04 Thread Laurence Rowe
I'm not very optimistic about this I'm afraid. First the problems with
using Plone:

 * Plone relies heavily on its in ZODB indexes of all content
(portal_catalog). This means that every edit will change lots of
objects (without versioning ~15-20, most of which are in the
catalogue).

 * At least with archetypes a content object's data is spread over
multiple objects. (This should be better with Dexterity, though you
will still have multiple objects for locking and workflow)

 * If you use versioning you'll see ~ 100 objects changed in an edit.

 * Even loading the front-page will take a long time - In my
experiments writing an amazon s3 backend for ZODB the extra latency of
fetching each object was really noticeable.

But I'm not sure even a simpler ZODB CMS would be a good fit for a p2p DHT:

 * ZODB is transactional using two phase commit. With p2p latencies,
these commits will be horribly slow - all clients storing changed
objects would need to participate in the transaction.

 * Each client's object cache will need to know about invalidations, I
don't see any way of supplying these from a DHT.

I expect you'd have more success storing content items as single
content objects / pages in the DHT and then generating indexes based
on that. You'll need some way of storing parent - child relationships
between the content objects too, as updating a single list of children
object will be incredibly difficult to get right in a distributed
system.

Laurence


On 4 January 2011 11:40, Aran Dunkley  wrote:
> Thanks for the feedback Vincent :-) it sounds like NEO is pretty close
> to being SQL-free. As one of the NEO team, what are your thoughts on the
> practicality of running Plone in a P2P environment with the latencies
> experienced in standard DHT (such as for example those based on
> Kademlia) implemtations?
>
> On 04/01/11 22:27, Vincent Pelletier wrote:
>> Hi.
>>
>> Le mardi 4 janvier 2011 07:18:34, Aran Dunkley a écrit :
>>> The problem is that it uses SQL for its indexing queries (they quote
>>> "NoSQL" as meaning "Not only SQL"). SQL cannot work in P2P space, but
>>> can be made to work on server-clusters.
>>
>> Yes, we use MySQL, and it bites us on both worlds actually:
>> - in relational world, we irritate developers as we ask questions like "why
>>   does InnoDB load a whole row when we just select primary key columns", 
>> which
>>   ends up with "don't store blobs in mysql"
>> - in key-value world, because NoSQL using MySQL doesn't look consistent
>>
>> So, why do we use MySQL in NEO ?
>> We use InnoDB as an efficient BTree implementation, which handles 
>> persistence.
>> We use MySQL as a handy data definition language (NEO is still evolving, we
>> need an easy way to tweak table structure when a new feature requires it), 
>> but
>> we don't need any transactional isolation (each MySQL process used for NEO is
>> accessed by only one process through one connection).
>> We want to stop using MySQL & InnoDB in favour of leaner-and-meaner 
>> back-ends.
>> I would especially like to try kyoto cabinet[1] in on-disk BTree mode, but it
>> requires more work than the existing MySQL adaptor and there are more urgent
>> tasks in NEO.
>>
>> Just as a proof-of-concept, NEO can use a Python BTree implementation as an
>> alternative (RAM-only) storage back-end. We use ZODB's BTree implementation,
>> which might look surprising as it's designed to be stored in a ZODB... But
>> they work just as well in-RAM, and that's all I needed for such proof-of-
>> concept.
>>
>> [1] http://fallabs.com/kyotocabinet/
>>
>> Regards,
>
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-04 Thread Matthias
Am 04.01.2011, 12:40 Uhr, schrieb Aran Dunkley :

> Thanks for the feedback Vincent :-) it sounds like NEO is pretty close
> to being SQL-free. As one of the NEO team, what are your thoughts on the
> practicality of running Plone in a P2P environment with the latencies
> experienced in standard DHT (such as for example those based on
> Kademlia) implemtations?

Something which may be worthwhile and give you an impression what the  
storage backend does for a common operation would be to instrument the  
ZODB code a bit. Just look at the current FileStorage and add a few log()s  
into its load/store methods. Maybe there are other methods of interest,  
too. Hooking this shouldn't take long.

Then I suggest you generate (or maybe you already have) a well-sized plone  
to test on. Perform a typical request on a site and see what the storage  
is doing. This will give you a solid idea what the storage has to do.

My guess (and I mostly infer this from the zodb code I've looked at) is  
that you can get many storage read requests for something like searching  
the catalog. I guess this will happen, because you get a load() call for  
each BTree bucket that you are traversing. Maybe I am totally wrong of  
course :) However, instrumenting the storage will show.

You might also find there are certain hotspots (like the catalog).  
Depending on their size you could make your users download these  
completely from the cloud before being able to use them. This would reduce  
the number of small randomly-seeking requests a lot.

Another thing you need to consider is implementing the transaction  
functionality. I'm not sure how to do something like this in the cloud or  
even if it's possible at all (given certain performance limitations).

And finally, my experiences using P2P is that it takes a while to build up  
speed for a certain download. And client uplinks are not as fast your  
typical web server's uplink. Also firewalls seem to cause problems  
sometimes (maybe workable with NAT punching?).

Maybe all of this is feasible in your situation, but this depends heavily  
on your requirements, usage and goals. Doing some fast prototyping and  
contacting authors who already wrote papers (or better implementations) is  
probably the best way to get solid a solid idea.

-Matthias
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-04 Thread Aran Dunkley
Thanks for the feedback Vincent :-) it sounds like NEO is pretty close
to being SQL-free. As one of the NEO team, what are your thoughts on the
practicality of running Plone in a P2P environment with the latencies
experienced in standard DHT (such as for example those based on
Kademlia) implemtations?

On 04/01/11 22:27, Vincent Pelletier wrote:
> Hi.
> 
> Le mardi 4 janvier 2011 07:18:34, Aran Dunkley a écrit :
>> The problem is that it uses SQL for its indexing queries (they quote
>> "NoSQL" as meaning "Not only SQL"). SQL cannot work in P2P space, but
>> can be made to work on server-clusters.
> 
> Yes, we use MySQL, and it bites us on both worlds actually:
> - in relational world, we irritate developers as we ask questions like "why
>   does InnoDB load a whole row when we just select primary key columns", which
>   ends up with "don't store blobs in mysql"
> - in key-value world, because NoSQL using MySQL doesn't look consistent
> 
> So, why do we use MySQL in NEO ?
> We use InnoDB as an efficient BTree implementation, which handles persistence.
> We use MySQL as a handy data definition language (NEO is still evolving, we 
> need an easy way to tweak table structure when a new feature requires it), 
> but 
> we don't need any transactional isolation (each MySQL process used for NEO is 
> accessed by only one process through one connection).
> We want to stop using MySQL & InnoDB in favour of leaner-and-meaner back-ends.
> I would especially like to try kyoto cabinet[1] in on-disk BTree mode, but it 
> requires more work than the existing MySQL adaptor and there are more urgent 
> tasks in NEO.
> 
> Just as a proof-of-concept, NEO can use a Python BTree implementation as an 
> alternative (RAM-only) storage back-end. We use ZODB's BTree implementation, 
> which might look surprising as it's designed to be stored in a ZODB... But 
> they work just as well in-RAM, and that's all I needed for such proof-of-
> concept.
> 
> [1] http://fallabs.com/kyotocabinet/
> 
> Regards,

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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Andreas Jung
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Marc Villemade wrote:
> Hey Andreas,
> 
> I don't know much about Aran's project, so you are right to wonder the 
> necessity to have yet another storage backend.
> Maybe he has needs and requirements that can't be fulfilled by the current 
> backends.


That's exactly the point: put the requirements on the desk and check
each of the existing storage backends against the requirements.
Then make a decision whether you really need a new storage
implementation or if there is a chance for using an existing solution
(or providing funding for feature extensions) or starting with a
complete a new project (taking possibly a long time (years) for becoming
mature enough for production).

- -aj
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Aran Dunkley
I have looked at NEO which is the closest thing I've found to the
answer, in fact NEO is why I felt Plone was the best choice of CMS to
inquire further about

The problem is that it uses SQL for its indexing queries (they quote
"NoSQL" as meaning "Not only SQL"). SQL cannot work in P2P space, but
can be made to work on server-clusters.

We intend not to have any machines in our network other than the users
computers running the P2P application. So we would need to know exactly
what kinds of querying ZODB expects to be available in its interface to
the storage layer. DHT's can be slow for the first read but cache
locally after that.


On 04/01/11 20:06, Andreas Jung wrote:
> Marc Villemade wrote:
>> Hey Andreas,
> 
>> I think it makes sense if the storage backend is hosted on-premise (hence 
>> private cloud), and i think that's what Aran is thinking about.
>> They could have Plone->ZODB->Storage backend in the same datacenter, hence 
>> no latency problem and good network throughput, provided that the cloud 
>> storage used is capable of offering high performance.
> 
> 
> First you should bring up arguments why the existing backends like ZEO,
> Relstorage or NEO are not good enough in your case. Looking at the
> development history of Relstorage or NEO: implementing an
> enterprise-level storage for the ZODB seems to be hard and
> time-consuming (and expensive).
> 
> -aj
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Marc Villemade
Hey Andreas,

I don't know much about Aran's project, so you are right to wonder the 
necessity to have yet another storage backend.
Maybe he has needs and requirements that can't be fulfilled by the current 
backends.

Aran, can you fill us in a little on the necessity of having a DHT ? What are 
the requirements you're trying to fulfill for your project ?

Cheers

-Marc
@mastachand
http://linkd.in/heve30




On Jan 3, 2011, at 11:06 PM, Andreas Jung wrote:

> -BEGIN PGP SIGNED MESSAGE-
> Hash: SHA1
> 
> Marc Villemade wrote:
>> Hey Andreas,
>> 
>> I think it makes sense if the storage backend is hosted on-premise (hence 
>> private cloud), and i think that's what Aran is thinking about.
>> They could have Plone->ZODB->Storage backend in the same datacenter, hence 
>> no latency problem and good network throughput, provided that the cloud 
>> storage used is capable of offering high performance.
> 
> 
> First you should bring up arguments why the existing backends like ZEO,
> Relstorage or NEO are not good enough in your case. Looking at the
> development history of Relstorage or NEO: implementing an
> enterprise-level storage for the ZODB seems to be hard and
> time-consuming (and expensive).
> 
> - -aj
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Andreas Jung
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Marc Villemade wrote:
> Hey Andreas,
> 
> I think it makes sense if the storage backend is hosted on-premise (hence 
> private cloud), and i think that's what Aran is thinking about.
> They could have Plone->ZODB->Storage backend in the same datacenter, hence no 
> latency problem and good network throughput, provided that the cloud storage 
> used is capable of offering high performance.


First you should bring up arguments why the existing backends like ZEO,
Relstorage or NEO are not good enough in your case. Looking at the
development history of Relstorage or NEO: implementing an
enterprise-level storage for the ZODB seems to be hard and
time-consuming (and expensive).

- -aj
-BEGIN PGP SIGNATURE-
Version: GnuPG v1.4.11 (Darwin)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Marc Villemade
Hey Andreas,

I think it makes sense if the storage backend is hosted on-premise (hence 
private cloud), and i think that's what Aran is thinking about.
They could have Plone->ZODB->Storage backend in the same datacenter, hence no 
latency problem and good network throughput, provided that the cloud storage 
used is capable of offering high performance.

Aran, are you thinking of developing your own DHT ?

Cheers

-Marc
@mastachand
http://linkd.in/heve30




On Jan 3, 2011, at 10:46 PM, Andreas Jung wrote:

> -BEGIN PGP SIGNED MESSAGE-
> Hash: SHA1
> 
> Aran Dunkley wrote:
>> I mean P2P as in using a DHT (distributed hash table) for its storage
>> layer so that it can run in a network composed only of the client users
>> with no web-server, the same way that the file-sharing programs such as
>> azzureus and aMule work. We can develop a basic wiki/blog in this way,
>> but would prefer a mature CMS like Plone.
> 
> As said: hard to achieve and it is highly questionable from the
> performance point of view having a distributed storage in the cloud.
> Applications like Plone basically require a storage backend with low
> network latency and good network throughput...so your idea is from my
> point of view neat but from the prospective of reality a a dead-horse
> from the beginning.
> 
> - -aj

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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Andreas Jung
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Aran Dunkley wrote:
> I mean P2P as in using a DHT (distributed hash table) for its storage
> layer so that it can run in a network composed only of the client users
> with no web-server, the same way that the file-sharing programs such as
> azzureus and aMule work. We can develop a basic wiki/blog in this way,
> but would prefer a mature CMS like Plone.

As said: hard to achieve and it is highly questionable from the
performance point of view having a distributed storage in the cloud.
Applications like Plone basically require a storage backend with low
network latency and good network throughput...so your idea is from my
point of view neat but from the prospective of reality a a dead-horse
from the beginning.

- -aj
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Aran Dunkley
I mean P2P as in using a DHT (distributed hash table) for its storage
layer so that it can run in a network composed only of the client users
with no web-server, the same way that the file-sharing programs such as
azzureus and aMule work. We can develop a basic wiki/blog in this way,
but would prefer a mature CMS like Plone.

On 04/01/11 18:34, Andreas Jung wrote:
> Aran Dunkley wrote:
>> I'm
>> wondering what you guys, the core developers, think of the
>> practicalities of Plone in P2P, for example could ZODB use a DHT as its
>> storage layer? what kind of querying is required on the DHT?
> 
> No idea what "P2P" means to you in particular.
> 
> The ZODB is a mandatory requirement for Plone as storage layer. You may
> work on storage layer implementation for the ZODB fulfilling your
> requirements (similar to Relstorage implementing a RDBMS backend for the
> ZODB). I have strong doubts that a "P2P" or (cloud-ish) backend is
> feasible as the ZODB is ACID compatible and ACID is basically something
> you can not achieve in the cloud or better spoken in a highly
> distributed environment.
> 
> -aj
> 
> 
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Re: [ZODB-Dev] Plone in P2P using Zope over DHT

2011-01-03 Thread Andreas Jung
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Aran Dunkley wrote:
> I'm
> wondering what you guys, the core developers, think of the
> practicalities of Plone in P2P, for example could ZODB use a DHT as its
> storage layer? what kind of querying is required on the DHT?

No idea what "P2P" means to you in particular.

The ZODB is a mandatory requirement for Plone as storage layer. You may
work on storage layer implementation for the ZODB fulfilling your
requirements (similar to Relstorage implementing a RDBMS backend for the
ZODB). I have strong doubts that a "P2P" or (cloud-ish) backend is
feasible as the ZODB is ACID compatible and ACID is basically something
you can not achieve in the cloud or better spoken in a highly
distributed environment.

- -aj


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