Threading issues with Hibernate

Question

I'm experiencing a strange behaviour with Hibernate. I've been banging my head against the wall for a while now, and will award any answer which leads to a solution with a +100 bounty.

I have a JAX-RS (Jersey) REST server, with a filter that associates one Hibernate-session per request.

In one request a client POSTs some data which is stored in the database using one session (and one transaction). In a subsequent call, the client tries to GET this entity, but Hibernate can't find it.

Some observations:

I can only reproduce this if I run multiple simultaneous clients. I've never managed to reproduce it by running one client at a time.)
I can see the entity ID in the database, and if I restart the server, the entity is found by Hibernate as it should.
The error does not occur if I use a thread pool of size 1 (regardless of how many clients I run simultaneously).

Here's the code, with some logging:

chargeables.setId(new SecureRandom().nextLong());

System.out.printf("%s,  session: %s  [%s]%n",
                  Thread.currentThread(),
                  System.identityHashCode(session),
                  "session.beginTransaction()");

session.beginTransaction();


System.out.printf("%s,  session: %s  [%s]%n",
                  Thread.currentThread(),
                  System.identityHashCode(session),
                  "session.save(id = "+chargeables.getId()+")");

session.save(chargeables);


System.out.printf("%s,  session: %s  [%s]%n",
                  Thread.currentThread(),
                  System.identityHashCode(session),
                  "session.getTransaction().commit()");

session.getTransaction().commit();

The code for getting the entity:

System.out.printf("%s,  session: %s  [%s]%n",
                  Thread.currentThread(),
                  System.identityHashCode(session),
                  "session.get("+id+")");

Chargeables entity = (Chargeables) session.get(Chargeables.class, id);

if (entity == null)
    System.out.printf("%s,  session: %s  [%s]%n",
                      Thread.currentThread(),
                      System.identityHashCode(session),
                      "ENTITY NOT FOUND!");

Now here is an excerpt of the resulting log (with some additional open/close session output):

Thread[Grizzly(5),5,main],  session:  2041842357  [factory.openSession()]
Thread[Grizzly(5),5,main],  session:  2041842357  [session.beginTransaction()]
Thread[Grizzly(5),5,main],  session:  2041842357  [session.save(id = 7939229356942262438)]
Thread[Grizzly(5),5,main],  session:  2041842357  [session.getTransaction().commit()]
Thread[Grizzly(5),5,main],  session:  2041842357  [session.close()]
[...]
Thread[Grizzly(7),5,main],  session:  1717445911  [factory.openSession()]
Thread[Grizzly(7),5,main],  session:  1717445911  [session.get(7939229356942262438)]
Thread[Grizzly(7),5,main],  session:  1717445911  [ENTITY NOT FOUND!]
Thread[Grizzly(7),5,main],  session:  1717445911  [session.close()]

Why on earth do I reach ENTITY NOT FOUND!?

Hibernate version: 4.1.9.Final
MySQL verison: 14.14 Distrib 5.5.29

Mapping file for Chargeables:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
       "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
       "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping
   default-cascade="all"
   package="se.package.common.chargeables"
   default-lazy="false">


    <class name="Chargeables">

        <id name="id" type="long">
            <generator class="assigned"/>
        </id>

        <property name="startTimeStamp" />
        <property name="endTimeStamp" />

        <list name="chargeables">
            <key column="chargeableId" />
            <list-index column="pos" />
            <many-to-many class="Chargeable"/>
        </list>

    </class>


    <class name="Chargeable">

        <id column="id" type="long">
            <generator class="native"/>
        </id>

        <discriminator />

        <property name="timestamp" />

    </class>


    <subclass name="DataTransfer" extends="Chargeable">
        <property name="bytesSent" />
        <property name="bytesReceived" />
    </subclass>


    <subclass name="TelephonyChargeable" extends="Chargeable">
        <many-to-one name="num" />
    </subclass>

    <subclass name="Call" extends="TelephonyChargeable">
        <property name="duration" />        
    </subclass>

    <subclass name="OutgoingCall" extends="Call" />
    <subclass name="IncomingCall" extends="Call" />

    <subclass name="Message" extends="TelephonyChargeable" />

    <subclass name="Sms" extends="Message" />
    <subclass name="IncomingSms" extends="Sms" />
    <subclass name="OutgoingSms" extends="Sms" />

    <subclass name="Mms" extends="Message" />
    <subclass name="IncomingMms" extends="Mms" />
    <subclass name="OutgoingMms" extends="Mms" />


</hibernate-mapping>

Have you turned on SQL logging for Hibernate? Dumb question: what's your ID generation strategy for this entity? — Sofian Djamaa
– Sofian Djamaa, Commented Apr 4, 2013 at 9:26
I haven't turned on SQL-logging. That's obviously a good idea. The generation strategy is "assigned". — aioobe
– aioobe, Commented Apr 4, 2013 at 9:31
code looks ok. Please show us the annotations you have for Chargeables or provide mapping file. to see what you have there. — sudmong
– sudmong, Commented Apr 4, 2013 at 9:41
Unable to access due to restriction on my network, please add it here. — sudmong
– sudmong, Commented Apr 4, 2013 at 9:46

Gab · Accepted Answer · 2013-04-04 13:08:27Z

0

IMHO it's an isolation problem. Your second session start before the transaction of the 1st one is commited. As default hibernate isolation level is read_commited, the 2nd session can't so retrieve the entity.
How are you passing id between the 2 threads ?

answered Apr 4, 2013 at 13:08

Gab

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4 Comments

aioobe Over a year ago

The client posts some data (the entity) which is persisted on the server. The response of this post is the ID of the persisted entity. In the second request the client tries to fetch this entity by providing the ID received from the previous request. If it is an isolation problem, can I change the isolation level so that it can be confirmed or ruled out?

Gab Over a year ago

It's not really standard : stackoverflow.com/questions/5234240/…. Don'k know which isolation levels are supported by Mysql. Regarding your comment above, isolation problem seems not very probable

Sofian Djamaa Over a year ago

If it's an isolation level issue I think a timeout would occur as the READ COMMITTED transaction waits for the other one to complete. See this post I've written about a similar issue: theoptimizerdiary.com/2013/03/31/…

Gab Over a year ago

Never seen this case, i suppose it depends on the isolation implementation of the underlying database. theoretically it should not wait anything, but return something missing the uncommited record

Community · Accepted Answer · 2017-05-23 12:12:54Z

If you can see the commit in the database, it cannot be an isolation issue at the MySQL level: console operations are also client operations, you don't get special powers when running them, so they conform to the isolation policy you selected.

Looking out for solution, I discovered that Hibernate provide some facilities to cache DB results: there are actually 2 levels of cache implemented there. Perhaps your hibernate installation comes bundled with a cache mechanism?

The first level works on a per session basis, which is consistent with the behaviour you observe when running the code on one thread, and seemingly happens to be activated by default. I am not Hibernate proficient, I can't say that for sure, but my opinion is that your setup has this first level of cache set in read-only mode, while you would like it to be in read-write mode.

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