为什么我打开的 ResultSet 在更改 session 后会自动关闭

Question

We have code that opens a ResultSet against a view in the Oracle root container, cdb$root . While the code iterates the rows, there is a use case where we need to perform a specific function call but this call must be made within the context of a specific plugable database, in our case ORCLDPB1 . Effectively the code looks like the following:

while (resultSet.next()) {
  LOGGER.info("ResultSet Closed (Top Of Loop): {}", resultSet.isClosed());
  if (someSpecialUseCaseIsTrue) {
    try (Statement s = connection.createStatement()) {
      LOGGER.info("ResultSet Closed (Creating new statement): {}", resultSet.isClosed());
      try {
        s.executeUpdate("ALTER SESSION SET CONTAINER=ORCLPDB1");
        LOGGER.info("ResultSet Closed (after alter session): {}", resultSet.isClosed());
        // perform some PDB specific operation
      }
      finally {
        s.executeUpdate("ALTER SESSION SET CONTAINER=cdb$root");
        LOGGER.info("ResultSet Closed (after alter back to root): {}", resultSet.isClosed());
      }
    }     
  }
}

The output is:

ResultSet Closed (Top Of Loop): false
ResultSet Closed (Creating new statement): false
ResultSet Closed (after alter session): true
ResultSet Closed (after alter back to root): true

Then when the while checks resultSet.next() on the second iteration this yields

java.sql.SQLException: Closed Resultset: next
    at oracle.jdbc.driver.InsensitiveScrollableResultSet.ensureOpen(InsensitiveScrollableResultSet.java:133)
    at oracle.jdbc.driver.InsensitiveScrollableResultSet.next(InsensitiveScrollableResultSet.java:428)

Through debugging, I've determined that the outer ResultSet remains open until the ALTER SESSION is executed and immediately afterward making call to isClosed() returns that the outer result-set is no longer open.

Is this behavior due to performing another operation while an existing ResultSet is open or is this because of the actual statement being executed, namely ALTER SESSION ? If the latter, why does this force a ResultSet to be invalidated?

Answer 1

From the Oracle "Administering a CDB with SQL*Plus" documentation :

40.2.3 Switching to a Container Using the ALTER SESSION Statement

...

The following are considerations for using the ALTER SESSION SET CONTAINER statement:

• ...
• If you open a cursor and use ALTER SESSION SET CONTAINER to switch to different container, then you cannot fetch data from that cursor until you switch back to the container in which the cursor was opened.

Answer 2

First of all I've checked simple scenario in SQL*Plus - it works fine:

SQL> alter session set container=pdb1;

Session altered.

SQL> create table test as select 1 a from dual;

Table created.

SQL> var c refcursor;
SQL> exec open :c for select * from test;

PL/SQL procedure successfully completed.

SQL> alter session set container=cdb$root;

Session altered.

SQL> alter session set container=pdb1;

Session altered.

SQL> print c

         A
----------
         1

As you can see I opened cursor in PDB1, switched to CDB$ROOT, then returned to PDB1 and successfully fetched from cursor.

So what exactly are you doing in // perform some PDB specific operation ? Are there any transactions?