[OJB-developers] Re: Bug in SequenceManager!!

[Thomas M. <tho...@ho...>]

Hi Satish,

Sorry for the problems OJB is causing!

This is really a severe bug. I'll have a look at it asap and will keep
you updated.

--Thomas

sa...@na... wrote:
> 
> Hi Thomas,
> 
> I have run into a particularly simple but nasty bug with
> SequenceManager very much on the same lines as the previous bugs I ran
> into with stale connections.
> 
> Basically, several database records have been overwritten (and have
> several people annoyed at me right now) as follows:
> 
> I use broker.getUniqueId(classname) to get the next id from OJB_SEQ
> table. However, broker.getUniqueId(..) calls
> m_Sequencemanager.getUniqueId(..)  in
> singlevm/PersistenceBrokerDefaultImpl.java.
> 
> The m_SequenceManager in the broker instance is obtained by using
> SequenceManagerFactory.getSequenceManager(this) in the broker
> constructor.
> 
> However, SequenceManagerFactory.getSequenceManager(broker) returns the
> static SEQMAN that it has created the first time it was used.  The
> broker argument is not used except for the first time. So, SEQMAN uses
> a broker instance that will potentially become stale due to idle
> connection timeout in mysql. Even without the timeouts,
> brokerInstance3.getUniqueId(..) will use brokerInstance1 for actually
> reading the next id from the db which does not seem right.
> 
> One fix that will be thread-safe is to add broker as an argument to
> SequenceManager.getUniqueId(classname, fieldname, broker).
> 
> Let me know what you think.
> 
> If you do have a quick fix/workaround for this, please let me know.
> I am under the gun right now.
> 
> -----------------------------------------------------------------
> 
> Now if you are interested, here is how several records have been
> overwritten due to this bug:
> 
> After a while after the web server was started, the cached broker
> instance in SEQMAN became stale and stopped updating (lets say
> sequence number = 50), the OJB_SEQ table.  However, due to poor
> exception/error handling in SequenceManagerDefaultImpl.getNextId(),
> getNextId() returned the in-memory copy of lastId+1 and hence
> everything seemed to be ok and did not throw the exception back to the
> application.
> 
> Now, a few days later (lets say we were at seq# = 150 at this time),
> the web server was restarted to update to ojb-0.5.200 and then the bad
> value (50) was read from OJB_SEQ and was updated for a while. So, the
> entries starting at 50 started getting overwritten.
> 
> Thanks,
> Satish.
> 
> --
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