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From Alexandru Popescu <the.mindstorm.mailingl...@gmail.com>
Subject Re: Thoughts on database persistence
Date Sun, 19 Mar 2006 03:14:36 GMT
Hi!

I am one of those that brought this subject to the ml in the past (unfortunately, no so detailed
as 
Jukka did).

I tend to agree with Jukka from the perspective of known j2ee best practices. Though, Stefan's

points are more important from functionality and performance point of view. What looks really

interesting is the fact that both ideas would work quite well together if:
- we can define a middle "persistence manager" layer that defines the needed atomic operations
(so 
this fullfils the requirement that all writes take place in the same transaction)
- we look at the current persistence manager as JDBC-like single operation provider.

With the above in mind, one will be able to define:
- in the higher level: how the connection is handled
- in the current pm layer: how the implementation (real persistence access) is handled

I would probably need more knowledge of the current implementation details in order to be
able to 
come out with a full proposal, but I really hope that the devs will hopefully understand what
I am 
trying to say.

hope this is more than 2c :-)

./alex
--
.w( the_mindstorm )p.


#: Stefan Guggisberg changed the world a bit at a time by saying (astral date: 3/18/2006 6:11
PM) :#
> On 3/18/06, Jukka Zitting <jukka.zitting@gmail.com> wrote:
>> Hi,
>>
>> I just added JNDI/DataSource -based versions of the database
>> persistence manager and file system classes as requested in JCR-313.
>> The comments on the issue thread got me thinking about the current
>> "simple" approach and database configurability in general. The
>> database file system classes are pretty much mirrors of the
>> persistence manager counterparts, so I'll just focus on the PM classes
>> here, the same ideas apply to both situations.
>>
>> The JCR-313 issue thread focused much on the question of
>> implementation "simplicity". After going throught the code I think the
>> question has more to do with the approach of keeping the database
>> connection throughout the PM lifecycle and caching prepared statements
>> for performance rather than any inherent simplicity of the
>> implementaion approach.
> 
> 'Simple' also refers to use of a very simple data model instead of
> a fully normalized schema or some object-relational mapping.
> 
>> The main point seems to be that the current
>> implementation wants to prepare the used statements once during
>> initialization rather than once per method call. This is somewhat in
>> conflict with the J2EE best practice of keeping a database connection
>> and related resources like prepared statements only for the duration
>> of a single operation.
> 
> those best practices apply to j2ee applications. the point is that i don't
> consider jackrabbit to be a j2ee application, jackrabbit is infrastructure
> and has other requirements regarding its persistence layer than a
> database application.
> 
>>
>> Incidentally there happens to be one approach that would keep the
>> performance advantages of the current approach, remove the conflict
>> with J2EE practices, and even simplify the implementation! Like this:
>>
>> 1) Change the DatabasePersistenceManager to get a database connection
>> and prepare the used statements per each operation to comply with J2EE
>> practices.
> 
> note that write operations must occur within a single transaction, i.e.
> you can't get a new connection for every write operation.
> 
>>
>> 2) Use the Commons DBCP DriverAdapterCPDS DataSource implementation
>> with PreparedStatement pooling in SimpleDbPersistenceManager to keep
>> the performance gains.
>>
>> 3) Remove the now unneeded Connection and PreparedStatement members
>> and resetStatement() method from the DatabasePersistenceManager class
>> to simplify the implementation.
>>
>> The cost of this change would be a bit of pooling overhead per each
>> persistence manager operation (should be insignificang compared to the
>> cost of the database operations) and the introduction of commons-dbcp
>> and commons-pool as dependencies.
>>
>> This change would also clarify that the responsibility of any extra
>> database shutdown operations like in the current
>> DerbyPersistenceManager rests on the subclass as the
>> DatabasePersistenceManager class would no longer keep any stable
>> reference to the underlying database.
>>
>> What do you think? I can take a shot at implementing this if you think
>> it's worth doing.
> 
> -1 for changing SimpleDbPersistenceManager as suggested right now
> 
> on the other hand i have problem with adding a new more sophisticated
> db pm as suggested.
> 
> time and experience will tell if we want to keep them both or not.
> 
> cheers
> stefan
> 
>>
>> BR,
>>
>> Jukka Zitting
>>
>> --
>> Yukatan - http://yukatan.fi/ - info@yukatan.fi
>> Software craftsmanship, JCR consulting, and Java development
>>
> 


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