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 <[EMAIL PROTECTED]> 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/ - [EMAIL PROTECTED]
Software craftsmanship, JCR consulting, and Java development
