Jboss XA Datasource with Oracle Can't Open Connection

Try following:switch off pad-xid (according to https://issues.jboss.org/browse/JBTM-1249 it should not be used for Oracle 11g)turn on no-tx-separate-pools (it helped with similar issue noted in https://community.oracle.com/thread/3558157)

Finally, I ran into the similar issue when using two Oracle xa-datasources using the same URL. When I changed one of the URLs (changed server name to IP address), issue "disappeared".

This works for me for Oracle 11.2.0.1.0 and WildFly 15

            <xa-datasource jndi-name="java:jboss/datasources/OracleDS" pool-name="OracleDS" enabled="true" statistics-enabled="true">                <xa-datasource-property name="URL">jdbc:oracle:thin:@127.0.0.1:1521:ORADB</xa-datasource-property>                <xa-datasource-property name="User">xxxx</xa-datasource-property>                <xa-datasource-property name="Password">xxxx</xa-datasource-property>                 <xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>                <driver>oracle</driver>                <transaction-isolation>TRANSACTION_READ_COMMITTED</transaction-isolation>                <driver>oracle</driver>                <xa-pool>                    <min-pool-size>10</min-pool-size>                    <max-pool-size>50</max-pool-size>                    <prefill>false</prefill>                    <use-strict-min>false</use-strict-min>                    <flush-strategy>FailingConnectionOnly</flush-strategy>                    <pad-xid>false</pad-xid>                    <wrap-xa-resource>true</wrap-xa-resource>                    <is-same-rm-override>false</is-same-rm-override>                </xa-pool>                                </xa-datasource>

Here is a description of the flags for your reference:

https://access.redhat.com/documentation/en-us/red_hat_jboss_operations_network/3.1/html/dev_complete_resource_reference/jbossas7-jbossas7_host_controller-profile-datasources_-profile--xadatasource_-profile-