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From "Simon Gash" <Simon.G...@gossinteractive.com>
Subject RE: [Jackrabbit Wiki] Update of "PersistenceManagerFAQ" by edgarpoce
Date Thu, 09 Jun 2005 10:24:45 GMT
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 ;)


-----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

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.


> 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
> >
> >=== 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
> >
> >=== 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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