=== Modify the {{book.project.name}} Datasource

After declaring your JDBC driver, you  have to modify the existing datasource configuration that {{book.project.name}} uses
to connect it to your new external database.  You'll do
this within the same configuration file and XML block that you registered your JDBC driver in.  Here's an example
that sets up the connection to your new database:

.Declare Your JDBC Drivers
[source,xml]
----
  <subsystem xmlns="urn:jboss:domain:datasources:4.0">
     <datasources>
       ...
       <datasource jndi-name="java:jboss/datasources/KeycloakDS" pool-name="KeycloakDS" enabled="true" use-java-context="true">
           <connection-url>jdbc:postgresql://localhost/keycloak</connection-url>
           <driver>postgresql</driver>
           <pool>
               <max-pool-size>20</max-pool-size>
           </pool>
           <security>
               <user-name>William</user-name>
               <password>password</password>
           </security>
       </datasource>
        ...
     </datasources>
  </subsystem>
----

Search for the `datasource` definition for `KeycloakDS`.  You'll first need to modify the `connection-url`.  The
documentation for your vendor's JDBC implementation should specify the format for this connection URL value.

Next define the `driver` you will use.  This is the logical name of the JDBC driver you declared in the previous section of this
chapter.

It is expensive to open a new connection to a database every time you want to perform a transaction.  To compensate, the datasource
implementation maintains a pool of open connections.  The `max-pool-size` specifies the maximum number of connections it will pool.
You may want to change the value of this depending on the load of your system.

Finally, with PostgreSQL at least, you need to define the database username and password that is needed to connect to the database.  You
may be worried that this is in clear text in the example.  There are methods to obfuscate this, but this is beyond the
scope of this guide.

NOTE:  For more information and details features of datasources, please see the link:{{book.appserver.datasource.link}}[the datasource configuration chapter]
       of the {{book.appserver.admindoc.name}}.