[jboss-jira] [JBoss JIRA] (WFLY-8041) CheckValidConnectionSQL can open a transaction, preventing application from changing transaction isolation level (PostgreSQL)

[Tomas Hofman (JIRA)]

Tomas Hofman created WFLY-8041:
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             Summary: CheckValidConnectionSQL can open a transaction, preventing application from changing transaction isolation level (PostgreSQL)
                 Key: WFLY-8041
                 URL: https://issues.jboss.org/browse/WFLY-8041
             Project: WildFly
          Issue Type: Bug
          Components: JCA
    Affects Versions: 10.1.0.Final
            Reporter: Tomas Hofman
            Assignee: Stefano Maestri


PostgreSQL driver only allows changing the transaction isolation level when transaction is not opened. Under certain circumstances, an application can receive a connection with already opened transaction and an attempt to change transaction isolation level will lead to exception.

This happens with the PostgreSQL driver and with CheckValidConnectionSQL checker configured to run a select statement to verify connections retrieved from the pool.

The scenario is as follows:

# A connection is retrieved from the pool for the 1st app and CheckValidConnectionSQL verifies it by running a select statement (autocommit is set to true by default). This statement is run directly via the jdbc connection, not the wrapper.
# 1st app receives the connection, sets autocommit=false, perform some work and commits a transaction.
# The connection is returned to the pool, {{cleanup()}} method is called on LocalManagedConnection wrapper, which sets autocommit=true. This however doesn't reset autocommit on the wrapped jdbc connection yet, which would only happen just before executing another SQL statement f.i.
# The same connection is retrieved from the pool for the 2nd app and CheckValidConnectionSQL runs the query. Because the jdbc connection has still autocommit=false, new transaction is opened.
# 2nd app receives the connection and calls {{setTransactionIsolation()}}, which throws an exception because the transaction is open.

Possible solution could be that the {{cleanup()}} method propagates the autocommit=true to the wrapped jdbc connection immediately.



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