What is the database?
Does your database supports nested transactions?
Regards.
----- Original Message -----
From: "Kaj Bjurman" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, January 31, 2001 1:30 PM
Subject: Transactions and locking...
> Hi
>
> I've got a problem with transaction propagation and pessimistic locking.
>
> The problem is as follows:
> A stateless session bean (SB1), with transaction attribute Required,
handles
> a call sequence.
> In that sequence it first calls anoter stateless session bean (SB2) which
> has transaction attribute NotSupported.
> SB2 gathers some data and performs validation. The data is gathered by
> calling en entity bean (EB1), which has
> transaction attribute Required. When the calling sequence returns to SB1,
> and the data is validated, and it calls
> yet another stateless session bean (SB3), which has transaction attribute
> RequiresNew.
> SB3 now performs some business logic, and then tries to update the data
> using EB1 (on the same PK as above).
> This results in a timeout (might be deadlock).
>
> The reason of the control flow is that the client call to SB1 should
result
> in several independent transactions,
> each started, and ended in SB3 (which the client can't call).
>
> See call sequence below:
>
> ------
>
> Notation:
> Bean(Type, Transaction Attribute)
>
> Beans in problem:
>
> SB1(Stateless Session, Required)
> SB2(Stateless Session, NotSupported)
> SB3(Stateless Session, RequiresNew)
> EB1(Entity, Required)
>
> Call sequence:
>
> Seq Caller Operattion Description:
>
> 1 Client Calls SB1 Client calls business method
> 2 SB1 Calls SB2 SB1 Uses SB2 to gather data for validation
> 3 SB2 Calls EB1 SB2 Uses EB1 to gather data for validation
> 4 SB1 Calls SB3 SB1 Then calls SB3 to perform the job
> 5 SB3 Calls EB1 SB3 Tries to use EB1 (Same pk as above) ->
> TimeOut, Lock...
> 6 SB1 Returns to client
> ------
>
> Isn't this what should happen (concerning the transactions):
>
> (seq above) Transactions
> 1 Transaction T1 starts
> 2 Transaction T1 suspends
> 3 Transaction T2 starts (EB1 gets involved in a transaction)
> Transaction T2 ends
> 4 Transaction T1 resumes
> 5 Transaction T3 starts (And tries to use EB1)
> Transaction T3 ends
> 6 Transaction T1 ends.
>
> But it looks like transaction T2 doens't start, or that the lock on EB1
> doesn't get released,
> and therefore EB1 that is used in T2, is still locked.
>
> Is the transaction sequence above correct, or have I misunderstood the
> specification?
>
> We are using weblogic, and the documentation for weblogic says:
> <Clip from Weblogic Docs.>
> The EJB 1.1 container in WebLogic Server Version 5.1 uses a pessimistic
> locking mechanism for entity EJB instances. As clients enlist an
> EJB or EJB method in a transaction, WebLogic Server places an exclusive
> lock on the EJB instance or method for the duration of the transaction.
> Other clients requesting the same EJB or method block until the current
> transaction completes.
> <End clip>
>
> But shouldn't the lock on EB1 be released in seq 3 (according to the EJB
> specification)?
>
> Thanks for your help
> /Kaj
>
> ~~~~~~~~~ ~~~~ ~~~ ~~ ~ ~ ~ ~
> [EMAIL PROTECTED]
> +46 70 4200148
>
>
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