title: javax.persistence.TransactionRequiredException: no transaction is in progress
body: <p>I've a service that store many objects into DB with HQL. But I've this exception</p>
  
  <pre><code>javax.persistence.TransactionRequiredException: no transaction is in progress
  at org.hibernate.ejb.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:789)
  at sun.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:601)
  at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:365)
  at $Proxy42.flush(Unknown Source)
  at sun.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:601)
  at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)
  at $Proxy42.flush(Unknown Source)
  at org.skyway.spring.util.dao.AbstractJpaDao.flush(AbstractJpaDao.java:90)
  at sun.reflect.GeneratedMethodAccessor16.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:601)
  at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
  at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
  at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
  at $Proxy52.flush(Unknown Source).........
  </code></pre>
  
  <p>May be the problem is a lot of number of concurrent operations active on DB.
  Any suggestions?</p>