I have an application using JPA EclipseLInk 2.5.2 which contacts every minute a mysql to do things. The first thing that has to be done is to say it's alive to the DB. To do this I use a ScheuledExecutorService running a busioness object every minute. This object opens an closes DAOs each time.
On my dev environment (my computer), with Wamp64 bits and mysql configured by default, everything is OK. When I put on a preprod server (CentOS 7, mysql Ver 14.14 Distrib 5.7.16), the first loop is OK, but the next ones fail with this message when trying to execute a sql query with a DAO :
[EL Warning]: 2016-12-13 09:35:01.936--UnitOfWork(1778154389)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet successfully received from the server was 57 316 milliseconds ago. The last packet sent successfully to the server was 4 milliseconds ago.
Error Code: 0
Call: SELECT id, lastDateAliveChargement, lastDateAliveDechargement FROM LastAlive
Query: ReportQuery(referenceClass=LastAlive sql="SELECT id, lastDateAliveChargement, lastDateAliveDechargement FROM LastAlive")
On preprod I used first a mariaDB used with the mariaDB jdbc driver. Then I switched to mysql with mysql jdbc driver, and I still got the problem. When I list the pending connections on the mysql they still appear with command Sleep until the wait_timeout is expired. I tried to configure mysql with these settings (my.cnf)
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
max_connections=100
port=3306
wait_timeout=3600
On my computer (wamp, so windows) : [mysql] no-auto-rehash //fails to start with this param on the server [mysqld] port = 3306
Here are the params for JPA initialization :
persistenceMapInitiales.put("javax.persistence.jdbc.driver","com.mysql.cj.jdbc.Driver");
persistenceMapInitiales.put("javax.persistence.jdbc.url","jdbc:mysql://MY_REMOTE_IP/myDB?characterEncoding=utf-8&useLegacyDatetimeCode=false&serverTimezone=UTC&autoReconnect=true&useSSL=false");
persistenceMapInitiales.put("javax.persistence.jdbc.user","toto");
persistenceMapInitiales.put("javax.persistence.jdbc.password","toto");
persistenceMapInitiales.put("eclipselink.ddl-generation","create-or-extend-tables");
persistenceMapInitiales.put("eclipselink.create-ddl-jdbc-file-name","createDDL_ddlGeneration.jdbc");
persistenceMapInitiales.put("eclipselink.drop-ddl-jdbc-file-name","dropDDL_ddlGeneration.jdbc");
persistenceMapInitiales.put("eclipselink.ddl.default-table-suffix","engine=InnoDB");
persistenceMapInitiales.put("eclipselink.ddl-generation.output-mode","both");
persistenceMapInitiales.put("eclipselink.connection-pool.default.initial","1" );
persistenceMapInitiales.put("eclipselink.connection-pool.default.min","64" );
persistenceMapInitiales.put("eclipselink.connection-pool.default.max","64" );
The declaration of the scheduledExectorService :
public static void main(String[] args)
{
final Integer CRON_PERIOD = 1; // every minute
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
scheduler.scheduleAtFixedRate(new MyWork(), 0, CRON_PERIOD, TimeUnit.MINUTES);
}
The Business class
public class MyWork() implements Runnable{
private LastAliveDao lastAliveDao;
//...
public void run()
{
sayIsAlive();
//...
}
private void sayIsAlive()
{
logger.info("upadet isAlive");
try{
lastAliveDao = new JpaLastAliveDao();
lastAliveDao.sayChargementIsAlive();
}catch(Exception e){
logger.error("", e);
}finally{
try{
lastAliveDao.close();
}catch(Exception e)
{
logger.warn("Exception closing dao : ", e);
}
lastAliveDao = null;
}
}
}
The DAO code :
public class JpaLastAliveDao extends JpaDao<LastAlive, Integer> implements LastAliveDao {
@Override
public void sayChargementIsAlive() {
List<LastAlive> alives = this.list();
if(alives.size() == 0){
LastAlive alive = new LastAlive();
alive.setLastDateAliveChargement(Calendar.getInstance().getTime());
this.persist(alive);
}else{
LastAlive alive = alives.get(0);
alive.setLastDateAliveChargement(Calendar.getInstance().getTime());
this.update(alive);
}
}
And the JpaDAO code :
public abstract class JpaDao<T, PK extends Serializable>
implements Dao<T, PK>{
protected Class<T> entityClass;
protected EntityManagerFactory emf;
protected EntityManager em;
@SuppressWarnings("unchecked")
public JpaDao()
{
emf = JPAUtils.getInstance("facturator").getEmf();
em = emf.createEntityManager();
ParameterizedType genericSuperclass = (ParameterizedType)
getClass().getGenericSuperclass();
this.entityClass = (Class<T>) genericSuperclass.getActualTypeArguments()[0];
}
public T persist(T t) {
this.em.getTransaction().begin();
this.em.persist(t);
this.em.getTransaction().commit();
return t;
}
public T findById(PK id) {
return this.em.find(entityClass, id);
}
public T update(T t) {
this.em.getTransaction().begin();
T entityPersist = this.em.merge(t);
this.em.getTransaction().commit();
return entityPersist;
}
@SuppressWarnings("unchecked")
public List<T> list()
{
return this.em.createQuery("SELECT t FROM "+entityClass.getName()+" t ").getResultList();
}
public void delete(T t) {
this.em.getTransaction().begin();
this.em.remove(t);
this.em.getTransaction().commit();
}
public void close(){
em.close();
}
}
OK I've found the reason. The DB server and the program server were configured on 2 differents submask network : 255.255.255.0 for one, and 255.255.255.255 for another one.
I found it with a SocketException that was not displayed in the stack with initial log settings.
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