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    <p>So I'll answer my own question with all the things I have found out lately.</p> <p>In order to understand server behavior, I changed my JBoss configuration to use a pool of only 1 connection, so I could detect when somebody else is blocked waiting.</p> <p>If the current operation is inside a transaction (e.g. @TransactionAttribute(REQUIRED)), the connection won't be used for anything else until the transaction finishes (other clients will have to wait). However, if you read the database without a transaction, other clients could grab the same connection while you are not using it, even before your business method finishes (I don't know how much of this behavior is standard and how much is an implementation detail).</p> <p>Hibernate does release the connection after every statement by default and that's why the connection can be reused in a non-transactional method. On the other hand, JDBC and JEE have the features needed to re-acquire the same connection if you are still in the same transaction.</p> <p>But why does Hibernate release a connection that it's going to re-acquire later? If Hibernate didn't release it, some JEE servers could think that Hibernate is leaking connections when it opens a connection in a nested EJB call and leaves it open for the caller to reuse. That is explained in this post:</p> <p><a href="http://www.mail-archive.com/hibernate-dev@lists.jboss.org/msg00612.html" rel="nofollow noreferrer">http://www.mail-archive.com/hibernate-dev@lists.jboss.org/msg00612.html</a></p> <p>To be safe, all data we need to save (and later present to the user) is explicitly passed as parameters, but for logging purposes we did use some data stored in the Oracle session, knowing that the connection cannot be reused by other clients as long as you use transactional business methods.</p> <p><strong>Update</strong>: It seems to be possible to do what I want using some app server specific settings related to connectors and/or custom data sources (not sure what is the best answer here: <a href="https://developer.jboss.org/thread/250132" rel="nofollow noreferrer">https://developer.jboss.org/thread/250132</a>)</p>
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    1. POSetting context in a JPA connection — is this safe?
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    1. COSomething like that would be very useful for DBAs. When using connection pools many fancy Oracle investigation tools are useless. DBAs can no more tell "Who, how and why is killing performance of DB server". But some of performance counters are also booked on MODULE account, so "we" would be able to tell which application's part is the most problematic. It would be also nice if it was possible to turn on session tracing (on Oracle side) for a particular transaction.
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    2. COWe've got it working, but there's yet another gotcha: nested EJB calls. If one EJB calls another EJB and both use the same interceptor, you must ensure that the **last** finally resets the context, not the first (as it would happen in a simplistic implementation). I used the TransactionSynchronizationRegistry to store a counter that's incremented on every call and decremented in the finally block.
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