Why does JBoss EAP create the number of max-pool-size + 1 connections?

Issue

• Why does JBoss EAP create the number of max-pool-size + 1 connections?
• We have an issue when we configure a XA datasource in a instance.

• XA-Datasource open more connection than configured.

• The XA datasource is configured with the following parameters:

                <xa-datasource jndi-name="java:/jdbc/testDS" pool-name="testDS" enabled="true">
                    <xa-datasource-property name="URL">xxxxxx</xa-datasource-property>
                    <xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>
                    <driver>oracle</driver>
                    <xa-pool>
                        <min-pool-size>2</min-pool-size>
                        <max-pool-size>2</max-pool-size>
                        <prefill>true</prefill>
                    </xa-pool>
                    <security>
                        <user-name>xxxxxx</user-name>
                        <password>***</password>
                    </security>
                    <validation>
                        <check-valid-connection-sql>select 1 from dual</check-valid-connection-sql>
                        <background-validation>true</background-validation>
                        <background-validation-millis>5000</background-validation-millis>
                    </validation>
                </xa-datasource>

                <drivers>
                    <driver name="oracle" module="com.oracle.db">
                        <xa-datasource-class>oracle.jdbc.xa.client.OracleXADataSource</xa-datasource-class>
                    </driver>
                </drivers>

• As shown in the configuration, the minimum and maximum number of connections is set at 2.
• When we start the instance, it sets 3 connections but the statistics only show 2:

[standalone@abcd:1010 xa-data-source=testDS] ls statistics=pool
ActiveCount=2             AverageCreationTime=2458  InUseCount=0              MaxWaitCount=0            TotalBlockingTime=0       
AvailableCount=2          CreatedCount=2            MaxCreationTime=3978      MaxWaitTime=0             TotalCreationTime=4917    
AverageBlockingTime=0     DestroyedCount=0          MaxUsedCount=1            TimedOut=0                
[standalone@abcd: 1010 xa-data-source=testDS]

• By firing SELECT query in Database Session it shows 3 connections as below:

SELECT MACHINE, logon_time from V$SESSION WHERE USERNAME='XXXXX' and MACHINE='***' order by machine;   


MACHINE                                                          LOGON_TIME
---------------------------------------------------------------- -----------
***                                                          13/05/2015 14:51
***                                                          13/05/2015 14:51
***                                                          13/05/2015 14:53

• What does this behavior due to?
• This issue is causing us some problems in production environment.