Hi,

I'm having a problem with my webapp that I think is caused by Hibernate. In a nutshell, when I update a database table outside the webapp, I don't see the updated data when I refresh the page. The data remains stale until I restart the whole webapp.

I have caching disabled:



I verified that Hibernate does actually query the database by printing out Hibernate session stats:



Finally, if I use a plain JDBC connection without Hibernate for the same query, the problem disappears... I would appreciate any suggestions and hope someone can shed some light on this problem.

how do u manage sessions? dont u have opened session for whole life of app?

and look in log for sql to see if hibernate does the query u expected

My sessions are opened and closed per each request. I have show sql set to true and I can see from the logs that hibernate does do the expected query for every request... but still comes back with stale data.

Are you sure the web page isn't being cached? :)

That was one of the first things I checked. :) Also, as I mentioned, I have show_sql enabled and I can see that the queries are being made.

Any other suggestions?

All out of sensible suggestions I'm afraid :)

I've experienced similar myself when using JPA - the caching being caused by the EntityManager holding the object graph in memory, in the case where you keep the EntityManager alive across multiple tx's.

If you then update the database in another thread using another EntityManager or via JDBC or whatever, the EntityManager cannot know about the update, and will continue to provide the cached stale objects (in response to queries that match the cached objects).

One thing you could try is using your debugger to look at the instance variables the Hibernate holds, just to make sure that after you close the session, the objects really have gone from memory and are not hanging around somewhere... just an idea. I guess you'd have to do this outside your web app.

So the update outside of the web app - are you sure this is committing the transaction that does the update to the database... if you verify the update by doing an insert then a select within the same transaction, it's going to look like the update works, but the web app won't see the update (assuming no caching) until the transaction is committed.

I do remember some similar problem where somebody had a delayed commit turned on in their database...

That's about the end of my guesses :)

Andy.

hi,

Have you tried to call session.clear(); before making your queries ?

@Andy

Thanks for the tips. I also believe that it's some caching issue. What puzzles me though, is that I have caching disabled. Also I'm not using JPA.

Re committing the tx, I verified it by querying the db directly, so the table gets updated for sure. + I tested the webapp using a plain JDBC connection which solves the problem - each request returns updated data.

@thiagodf

session.clear() didn't make a difference unfortunately...

Try start a tx even before perform a select using hibernate...

If I had to much money I'd bet you are using an old session/transaction.

Try the following to hunt down the problem:

1. enable cache logging. to see that really no 2nd level cache is used.
2.enable caching to check that the logging is working.
3. disable caching again.
4. when getting the new Session print it out to log/console and compare with the value from the previous request, to make sure you get a new one every time.
5. before the select in question use session.getStatistics to ensure the objects you are about to select aren't already in the session.

Jens

Hi Jens,

Thanks for the pointers. I've verified through the logs that caching is disabled:



And the statistics confirm this also. Main things to note is that sessions are opened and closed properly, a database query is made on each request, and there are no cache puts/hits/misses.



I still haven't figured out what's causing this problem, so any other suggestions would be most welcome.

Explain the sequence of the things and explain how it works with jdbc. I'd like to know how you get connections, how the sql is executed in both cases, what the db is, what is the full hibernate configuration file and all the log you see.



Farzad-

try using
(UrObject) session.get(UrObject.class, idOfUrObject);
instead of
(UrObject) session.load(UrObject.class, idOfUrObject);

greets

Tim

Suggestion: Log all your sql-statements (and the regarding result-sets) with p6spy.
As first step plaase analyze the result-sets to see if it is the database which returns you stale data (in this case it may a problem of isolation level) or if it is hibernate returning stale data (hibernate internally within a persistent context simulates a repeatable read isolation behavior, unless you call clear)