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From Serge Huber <shub...@jahia.com>
Subject Re: [Jackrabbit Wiki] Update of "PersistenceManagerFAQ" by edgarpoce
Date Thu, 09 Jun 2005 10:35:58 GMT

Ok thanks guys for the positive feedback. I must say I was beginning to 
wonder if I should continue spending my time on it or not, but it looks 
like there is some interest so I will keep on. As I have said I have a 
lot of other projects going on at work and I'm always a little behind on 
the latest and greatest in the JCR, but I do like this JSR so in any 
form I want to stay involved.

Regards,
  Serge Huber.

Simon Gash wrote:

>Serge, I know clients who won't be interested in any other option but
>the ORM PM. There are loads of reasons why this type of PM offers a good
>solution. The important point is that there will never be a one size
>fits all PM solution hence a pluggable strategy (ooops sorry stefan...)
>is an excellent idea.
>
>Come on Madhu give the guy some positive feedback !!!
>
>Anyway, as soon as you are happy with it we'll be downloading it and
>running it...surely that must rate as some positive karma ;)
>
>
>Simon
>
>-----Original Message-----
>From: Stefan Guggisberg [mailto:stefan.guggisberg@gmail.com] 
>Sent: 09 June 2005 11:11
>To: jackrabbit-dev@incubator.apache.org
>Subject: Re: [Jackrabbit Wiki] Update of "PersistenceManagerFAQ" by
>edgarpoce
>
>On 6/9/05, Serge Huber <shuber2@jahia.com> wrote:
>  
>
>>Maybe it's me overreacting (I do have a lot of pressure at work right
>>now) but I'm getting a lot of negative karma about the ORM-PMs... If 
>>they are not to most people tastes, maybe we should just remove them ?
>>
>>For me it was mostly a way to propose quickly a new back-end to 
>>Jackrabbit and get my hands dirty with the project. But if most people
>>    
>>
>
>  
>
>>on the project feel that they "add unnecessary complexity", or "are 
>>not the right way to go", then maybe they should be removed ?
>>    
>>
>
>don't worry, serge. i admit that i am not a huge fan of object
>relational databases and sorts but that's also a question of personal
>taste i guess. 
>i don't have a problem with ORM PM in contrib and there seems to be
>interest in it.
>
>cheers
>stefan
>
>  
>
>>Regards,
>>  Serge Huber.
>>
>>Apache Wiki wrote:
>>
>>    
>>
>>>Dear Wiki user,
>>>
>>>You have subscribed to a wiki page or wiki category on "Jackrabbit
>>>      
>>>
>Wiki" for change notification.
>  
>
>>>The following page has been changed by edgarpoce:
>>>http://wiki.apache.org/jackrabbit/PersistenceManagerFAQ
>>>
>>>New page:
>>>= PersistenceManager(PM) FAQ =
>>>The responses were mainly gathered from the jackrabbit mailing list.
>>>
>>>=== What's a PM? ===
>>>The PM is an *internal* Jackrabbit component that handle the
>>>      
>>>
>persistent storage of content nodes and properties. Each workspace of a
>Jackrabbit content repository uses a separate persistence manager to
>store the content in that workspace. Also the Jackrabbit version handler
>uses a separate persistence manager. The PM sits at the very bottom
>layer in jackrabbits system architecture.
>  
>
>>>Reliability, integrity and performance of the PM are *crucial* to the
>>>      
>>>
>overall stability & performance of the repository. If e.g. the data that
>a PM is based upon is allowed to change through external means the
>integrity of the repository would be at risk (think of referential
>integrity / node references e.g.).
>  
>
>>>=== What's the PM responsibility? === The PM interface was never 
>>>intended as being a general SPI that you could implement in order to
>>>      
>>>
>integrate external datasources with proprietary formats (e.g. a
>customers database). the reason why we abstracted the PM interface was
>to leave room for future performance optimizations that  would not
>affect the rest of the implementation (e.g. by storing the raw data in a
>b-tree based database instead of individual file).
>  
>
>>>=== How smart should be a PM? ===
>>>A PM should not be 'intelligent', it should not 'interpret' the data.
>>>      
>>>
>The only thing it should care about is to efficiently, consistently and
>reliably store and read the data encapsulated in the passed nodeState &
>propertyState objects. Though it might be feasible to write a custom
>persistence manager to represent existing legacy data in a level-1
>(read-only) repository, I don't think the same is possible for a level-2
>repository and i certainly would not recommend it.
>  
>
>>>=== What about ORM-backed PMs? ===
>>>Persistence managers that store the item states in a complex schema
>>>      
>>>
>are not the right way to go. Keep it simple, e.g. the
>objectPersistenceManager stores the item states as a raw stream of
>bytes.
>  
>
>>>=== What combination of FS and PM is the best choice? === It depends 
>>>on your priorities. If you want to store your data in an accessible
>>>      
>>>
>format (just in case ;), you might want to try XML PM + localFileSystem.
>If you use windows and performance is a must, you might want to try
>objectPersistenceManager + cqfs.
>  
>
>>>=== Which are the current options? What are the status, pros and cons
>>>      
>>>
>
>  
>
>>>of each implementation? ===
>>>
>>>=== objectPersistenceManager ===
>>>* Status: mature
>>>* Simple
>>>* Not human readable
>>>* An inconsistency is hard to fix without a tool
>>>* easy to configure
>>>* Write operations are synchronized
>>>* if the jvm process is killed the repository might turn 
>>>inconsistent
>>>* non transactional
>>>
>>>=== xml persistenceManager ===
>>>* Status: mature
>>>* not so simple but human readable
>>>* easy to configure
>>>* Write operations are synchronized
>>>* if the jvm process is killed the repository might turn 
>>>inconsistent
>>>* non transactional
>>>
>>>=== ORM persistenceManagers ===
>>>* Status: work in progress
>>>* Unnecessary complexity
>>>* transactional
>>>* rdbms referencial integrity (possible, but not implemented yet)
>>>* not so easy to configure.
>>>* Multithreaded friendly. Write operations don't need to be
>>>      
>>>
>synchronized.
>  
>
>>>=== localFileSystem: ===
>>>* Status: mature
>>>* Slow on window boxes
>>>
>>>=== CQFS file system ===
>>>* Status: mature
>>>* Mysterious configuration options ;)
>>>* Mysterious proprietary binary format ;)
>>>* fast on windows
>>>* license issue, it's proprietary
>>>
>>>
>>>
>>>      
>>>
>>    
>>
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