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From Alexandros Karypidis <akary...@yahoo.gr>
Subject Re: Fetch database changes from external sources
Date Fri, 16 May 2008 07:18:24 GMT
I must say this is beginning to look like a bug to me.

The reason is that the code snippet provided works with no problems when 
using Hibernate & Toplink Essentials (it is company policy where I work 
that we stick to pure JPA API and for that reason we test our code 
against OpenJPA, Hibernate & Toplink Essentials).

If somebody doesn't point out something I am doing wrong in the next 
couple of days, I will file a bug report with my snippet as an 
attachment (the code to reproduce this is about 50 lines, including the 
entity class Record, the Main class with the test code and the 
persistence.xml file).

Alexandros Karypidis wrote:

> Hello all,
> 
> I used the information provided to test the "DataCache" or "2nd-level" 
> cache. The cache doesn't seem to be the problem.
> 
> I added the following to the persistence.xml:
> 
>     <property name="openjpa.DataCache" value="true" />
>     <property name="openjpa.RemoteCommitProvider" value="sjvm"/>
>     <property name="openjpa.QueryCache" value="true" />
>     <property name="openjpa.Log"
>         value="SQL=TRACE, DataCache=TRACE" />
> 
> I also tried with the cache disabled (value="false" for 
> openjpa.DataCache) and in both cases refresh() does nothing.
> 
> With the cache enabled, a cache hit is logged. With the cache disabled, 
> no DataCache logging channel messages are produced. In both cases, no 
> SQL is executed to re-fetch the object.
> 
> Here is the log output with the cache DISABLED
> ===========================================================
> 937  testOpenJPA  TRACE  [main] openjpa.jdbc.SQL - <t 31365828, conn 
> 25345246> executing prepstmnt 9030750 SELECT t0.strField FROM Record t0 
> WHERE t0.recId = ? [params=(int) 1]
> 937  testOpenJPA  TRACE  [main] openjpa.jdbc.SQL - <t 31365828, conn 
> 25345246> [0 ms] spent
> RECORD 1 EXISTS, VALUE: Rec 1
> PRESS ENTER TO REDISPLAY...
> RECORD 1 EXISTS, VALUE: Rec 1
> ===========================================================
> 
> 
> Here is the log output with the cache ENABLED
> ===========================================================
> 859  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache miss while 
> looking up key "1".
> 922  testOpenJPA  TRACE  [main] openjpa.jdbc.SQL - <t 23860799, conn 
> 19432672> executing prepstmnt 5324129 SELECT t0.strField FROM Record t0 
> WHERE t0.recId = ? [params=(int) 1]
> 922  testOpenJPA  TRACE  [main] openjpa.jdbc.SQL - <t 23860799, conn 
> 19432672> [0 ms] spent
> 937  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache miss while 
> looking up key "1".
> 937  testOpenJPA  TRACE  [main] openjpa.DataCache - Put key "1" into cache.
> 937  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache hit while 
> looking up key "1".
> RECORD 1 EXISTS, VALUE: Rec 2
> PRESS ENTER TO REDISPLAY...
> 6451  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache hit while 
> looking up key "1".
> 6451  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache hit while 
> looking up key "1".
> 6467  testOpenJPA  TRACE  [main] openjpa.DataCache - Cache hit while 
> looking up key "1".
> RECORD 1 EXISTS, VALUE: Rec 2
> ===========================================================
> 
> Drew Lethbridge wrote:
> 
>> Gday - They're talking about the DataCache.  Check out the docs here:
>>
>> http://openjpa.apache.org/docs/latest/manual/ref_guide_caching.html
>>
>> In your scenario, you might want to disable the datacache, or employ 
>> datacache timeouts or eviction.
>>
>> cheers!
>>
>> ..droo.
>>
>> On 15/05/2008, at 8:52 PM, Alexandros Karypidis wrote:
>>
>>> Hi,
>>>
>>> First of all, thanks for the input.
>>>
>>> 1) I am not sure what the second-level cache is. Going through the 
>>> user manual and searching the web did not help. All I could find that 
>>> is cache-related are the following properties, which I set as follows 
>>> (hoping that they indeed control the "second-level cache"):
>>>
>>>     <property name="openjpa.DataCache" value="false"/>
>>>     <property name="openjpa.QueryCache" value="false"/>
>>>
>>>
>>> 2) As far as calling evict is concerned, I added these calls between 
>>> the two find() calls:
>>>
>>>     OpenJPAEntityManagerFactory jemFactory =
>>>         (OpenJPAEntityManagerFactory) emFactory;
>>>     jemFactory.getQueryResultCache().evictAll();
>>>     jemFactory.getStoreCache().evictAll();
>>>         OpenJPAEntityManager jem = (OpenJPAEntityManager) em;
>>>     jem.evictAll(Record.class);
>>>
>>> Neither modification helped and as far as the second approach is 
>>> concerned, I would prefer to restrict my code to standard JPA only.
>>>
>>> In any case OpenJPA still uses some cache to return the object the 
>>> second time around.
>>>
>>> Can you point me towards something more concrete regarding this 
>>> "second level cache" and how to disable it? Is it perhaps referred to 
>>> by some other name? I really couldn't find information when 
>>> web-searching for stuff like "openjpa second level cache".
>>>
>>> Thanks again for your time.
>>>
>>> Craig L Russell wrote:
>>>
>>>> Hi,
>>>> It sounds like you're using the second-level cache which is 
>>>> dutifully returning the current contents that are cached.
>>>> Have you tried using the evict methods of the second level cache, or 
>>>> disabling it for the application?
>>>> Craig
>>>> On May 14, 2008, at 2:37 AM, Alexandros Karypidis wrote:
>>>>> Hi,
>>>>>
>>>>> First of all, I've done research through the archives for the 
>>>>> situation I am facing and found this:
>>>>>
>>>>> http://mail-archives.apache.org/mod_mbox/openjpa-users/200706.mbox/%3C7262f25e0706152022u4942a14dkec98e30b520350b7@mail.gmail.com%3E

>>>>>
>>>>>
>>>>> I am facing the exact problem mentioned in that thread: I need to 
>>>>> fetch an object several times from the database, whose columns are 
>>>>> updated from another program and pick up the changes made by that 
>>>>> program. However, I can't get OpenJPA to re-execute SQL and 
>>>>> retrieve the object's new data from the database.
>>>>>
>>>>> In the thread of the link I provide, I was lead to believe that 
>>>>> em.refresh(obj) should do the trick. However, OpenJPA does not 
>>>>> execute any SQL (I have SQL=TRACE in the log options and I only see 
>>>>> one select statement) and keeps the old data in the object.
>>>>>
>>>>> I use OpenJPA release 1.0.2 and the code snippet with which I test 
>>>>> is the following:
>>>>>
>>>>> =========================================================
>>>>> EntityManagerFactory emFactory =
>>>>>    Persistence.createEntityManagerFactory(PERSISTENCE_UNIT);
>>>>> EntityManager em = emFactory.createEntityManager();
>>>>>
>>>>> Record r = em.find(Record.class, 1);
>>>>> System.out.println("VALUE: " + r.getStrField());
>>>>>
>>>>> System.out.print("PRESS ENTER TO REDISPLAY...");
>>>>> BufferedReader stdin = new BufferedReader(new InputStreamReader(
>>>>>        System.in));
>>>>> stdin.readLine();
>>>>>
>>>>> // ------> PROBLEM AREA <------
>>>>> em.refresh(r); // does not work
>>>>> // ((OpenJPAEntityManager)em).evict(r); // also does not work
>>>>> // em.clear(); // works but detaches everything
>>>>> // em.close(); // ... re-create. works, costs too much
>>>>> // ------> PROBLEM AREA <------
>>>>>
>>>>> r = em.find(Record.class, 1);
>>>>> System.out.println("VALUE: " + r.getStrField());
>>>>> =========================================================
>>>>>
>>>>> I change the strField of the "Record" object using a database 
>>>>> editor before I press enter to re-fetch the value.
>>>>>
>>>>> So, my question is, why does OpenJPA ignore the call to refresh() 
>>>>> if the object is still attached? I don't see it as reasonable to 
>>>>> detach all objects just to pick up a change in the database. I 
>>>>> figured it may be a transaction isolation issue, but then did the 
>>>>> following test which also did not work:
>>>>>
>>>>> =========================================================
>>>>> EntityManagerFactory emFactory =
>>>>>    Persistence.createEntityManagerFactory(PERSISTENCE_UNIT);
>>>>> EntityManager em = emFactory.createEntityManager();
>>>>>
>>>>> em.getTransaction().begin();
>>>>> Record r = em.find(Record.class, 1);
>>>>> System.out.println("VALUE: " + r.getStrField());
>>>>> em.getTransaction().commit();
>>>>>
>>>>> System.out.print("PRESS ENTER TO REDISPLAY...");
>>>>> BufferedReader stdin = new BufferedReader(new InputStreamReader(
>>>>>        System.in));
>>>>> stdin.readLine();
>>>>>
>>>>> em.getTransaction().begin();
>>>>> r = em.find(Record.class, 1);
>>>>> em.refresh(r);
>>>>> em.getTransaction().commit();
>>>>> System.out.println("VALUE: " + r.getStrField());
>>>>> =========================================================
>>>>>
>>>>> So even when reading the object through 2 different transactions, I 
>>>>> still can't get its data to be re-fetched...
>>>>>
>>>>> Funilly enough, if i call rollback() on the transaction, it does 
>>>>> work! However, it seems too much of a kludge to base my solution on 
>>>>> that...
>>>>>
>>>>> Thanks in advace to anyone who takes the time to help out.
>>>>>
>>>> Craig Russell
>>>> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
>>>> 408 276-5638 mailto:Craig.Russell@sun.com
>>>> P.S. A good JDO? O, Gasp!
>>>
>>>
>>
>>
> 
> 


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