sample: use c3p0 for connection pooling

Author: morgwai

sample/pom.xml

@@ -95,6 +95,12 @@
 			<version>[2.2.220,2.999.9999]</version>
 			<scope>runtime</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.hibernate</groupId>
+			<artifactId>hibernate-c3p0</artifactId>
+			<version>[5.6.10.Final,5.999.999.Final]</version>
+			<scope>runtime</scope>
+		</dependency>
 	</dependencies>
 
 	<build>

sample/src/main/resources/META-INF/persistence.xml

@@ -20,8 +20,8 @@
 					value="drop-and-create"/>
 			<property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect" />
 			<property name="hibernate.show_sql" value="true" />
-			<!-- WARN: this uses hibernate internal connection pool, not suitable for production -->
-			<property name="hibernate.connection.pool_size" value="3" />
+			<property name="hibernate.c3p0.maxPoolSize" value="3" />
+			<property name="hibernate.c3p0.maxStatementsPerConnection" value="5" />
 		</properties>
 	</persistence-unit>
 </persistence>