Re: a simple example of XA (not working)

Luca Ferrari wrote:
> Hi all,
> I'm trying to build a simple "manual" example of the use of the XA extension,
> the following is the code:
>
> PGXADataSource dataSource = new PGXADataSource();
> dataSource.setDatabaseName("hrpm");
> dataSource.setUser("luca");
> dataSource.setServerName("localhost");
>
> XAConnection connection = dataSource.getXAConnection();
> System.out.println("Connesso!");
> XAResource resource = connection.getXAResource();
> MyXid identifier = new MyXid();
> identifier.setBranchQualifier(new byte[] {0x01, 0x02, 0x03, 0x04, 0x05});
> identifier.setGlobalTransactionId(new byte[] {0x05, 0x04, 0x03, 0x02, 0x01});
> identifier.setFormatId(100);
>
> try{
> resource.start(identifier, XAResource.TMNOFLAGS);
>
>
> Connection jdbcConnection = connection.getConnection();
> Statement statement = jdbcConnection.createStatement();
> String sql = "INSERT INTO ...";
> int inserted = statement.executeUpdate(sql);
>
> resource.end(identifier, XAResource.TMSUCCESS);
>
> int commit = resource.prepare(identifier);
> if( commit == XAResource.XA_OK )
> resource.commit(identifier, false);
> else
> resource.rollback(identifier);
>
>
> now the exception that is raised when the program commits the transaction is
> the following:
>
> javax.transaction.xa.XAException: org.postgresql.util.PSQLException: ERROR:
> prepared transaction with identifier "100_BQQDAgE=_AQIDBAU=" does not exist
> at org.postgresql.xa.PGXAConnection.commitPrepared(PGXAConnection.java:412)
> at org.postgresql.xa.PGXAConnection.commit(PGXAConnection.java:339)
>
> and the log of the database says:
>
> 2007-06-16 16:05:48 CEST LOG: execute <unnamed>: INSERT INTO ....
> 2007-06-16 16:05:48 CEST LOG: execute <unnamed>: PREPARE
> TRANSACTION '100_BQQDAgE=_AQIDBAU='
> 2007-06-16 16:05:48 CEST WARNING: non c'è nessuna transazione in corso
> 2007-06-16 16:05:48 CEST LOG: execute <unnamed>: COMMIT
> PREPARED '100_BQQDAgE=_AQIDBAU='
> 2007-06-16 16:05:48 CEST ERROR: prepared transaction with
> identifier "100_BQQDAgE=_AQIDBAU=" does not exist
> 2007-06-16 16:05:48 CEST STATEMENT: COMMIT PREPARED '100_BQQDAgE=_AQIDBAU='
> 2007-06-16 16:05:49 CEST LOG: unexpected EOF on client connection
>
> that is an error since it seems no one transaction has been started. However,
> debugging the application, I've seen that the driver disables the autocommit
> mode, thus where is the problem here?
> I'm sorry, I'm not a XA expert, just learning.

This seems to be an undesired side-effect of this patch that was
committed in December:

> date: 2006/12/01 10:13:46; author: jurka; state: Exp; lines: +19 -22
> A XAConnections default autocommit state should be true. The
> driver was previously setting autocommit to false and assuming it
> would stay that way. This caused two problems. First, some
> applications expected to be able to issue local autocommit
> transactions prior to begin(). Second, some TMs (Geronimo) set the
> autocommit state to true themselves, which causes problems as the
> driver did not expect it to be changed. This patch correctly disables
> and enables autocommit around begin, prepare, commit, and rollback
> methods.

getConnection sets autocommit to false, so even though start set it to
true, it's reset to false in the call to getConnection. Attached patch
fixes that by explicitly setting autocommit to the right mode in
PGXAConnection.getConnection.

As a work-around, just call jdbcConnection.setAutoCommit(false) in your
program before executing any queries.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com