According to the docs, the defaultAutoCommit is a configuration property for the ConnectionPoolDatasource. The org.postgresql.ds.PGConnectionPoolDataSource class in the postgresql-8.3dev-600.jdbc3.jar has methods to get and set this property.
http://www.postgresql.org/docs/7.3/interactive/jdbc-datasource.html
The DataSource and XADataSource does not have this property and cannot be used with these resource types.
Could you please attach your configuration, if you used the ConnectionPoolDataSource and it failed?
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