Hi,
Many thanks for your response.
> no, but you may use locks to further control isolation level.
There seems to be at least two problems with that approach :
- You will get a (unpleasant) javax.jcr.lock.LockException if another
transaction tries to lock the node (or a child).
- It is not enforced even though it should be used everywhere, even for
only a read.
> I cannot quite follow you here. thread B seems to save a session without
having
> made changes to it? that means 'B : save session' is basically no op.
But I guess
> that's not what you want to know...
Sorry there was an error in my example. I should make more sense this way :
Example v.2 :
A : open session
A : read nodes "test" & "test2"
B : open session
B : delete nodes "test" & "test2"
B : save session //WHAT SHOULD HAPPEN ??
B : logout
A : read nodes "test" & "test2" //WHAT SHOULD HAPPEN ??
A : logout
It would be useful if the isolation level could configured at the
repository level. So if your application needs better isolation or
performance you would only need to change the configuration and not your code.
An implementation could (hypothetically) use locks in SessionImpl and use
events (when a session saves/logout) to prevent throwing exceptions. A
queue would hold pending operations. However, we would have to be careful
about long lived sessions...
What do you think ?
Regards,
Nicolas
Le 04:06 2005-07-08, vous avez écrit:
Hi Nicolas,
Nicolas Belisle wrote:
What is the session isolation level [ref.
http://www.unix.org.ua/orelly/java-ent/ebeans/ch08_03.htm] by default ?
the default is read commited.
Is it configurable ?
no, but you may use locks to further control isolation level.
a session in jackrabbit will see changes as soon as they are committed.
you may however use locks to achieve a higher isolation level.
successfully setting a lock on a node will give you repeatable read for
that subtree. if you do that on the root node you get serializable
isolation level.
At least, Jackrabbit seems to prevent dirty reads (determined from
tests). Is there any documentation regarding isolation level ? I think it
is a very important topic...
Unfortunately there is currently no documentation on isolation levels, but
this thread may be a good starting point to collect all relevant
information and then put it into a nice xdoc or wiki page.
Example :
A : open session
A : read nodes "test" & "test2"
B : open session
A : delete nodes "test" & "test2"
B : save session //WHAT SHOULD HAPPEN ??
B : logout
A : read nodes "test" & "test2" //WHAT SHOULD HAPPEN ??
A : logout
I cannot quite follow you here. thread B seems to save a session without
having made changes to it? that means 'B : save session' is basically no
op. But I guess that's not what you want to know...
regards
marcel
