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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Duplicate Key Problem
Date Thu, 13 Jul 2006 20:54:13 GMT
Hi,

This might be a really random suggestion, but couldn't you use the  
following strategy, even with autocommit=true?

public long getNextKey() {
  boolean conflict = true;
  while (conflict) {
   key = SELECT current_key_value from auto_pk_table
   next_key = key + increment;
   UPDATE auto_pk_table SET current_key_value = next_key_value WHERE  
current_key_value = key
   conflict = 0 rows updated
}
  return next_key;
}

All you worry about here is making sure that your increment is large  
enough to avoid frequent conflicts.

Craig

On Jul 13, 2006, at 6:17 AM, Gentry, Michael (Contractor) wrote:

> The basic strategy to refresh the primary key cache in MySQL is:
>
> * lock table
> * select next key values from auto_pk_support
> * update auto_pk_support with a new next key (20 keys by default)
> * unlock table
>
> I was just looking at the MySQL docs for "LOCK TABLES" and it  
> appears to
> work differently with InnoDB.  Which DB storage type are you using?
> Also, Andrus' suggestion that there could've been a failure with the
> connection going down could be correct.  It would've happened between
> select and update above.  An application got 20 PKs, but the  
> connection
> was broken before it could update the PK table.  Another application
> comes along and gets the same 20 PKs.
>
> Any chance you can use PostgreSQL?  It uses sequences which are atomic
> operations.
>
> Thanks,
>
> /dev/mrg
>
> PS. Andrus: If a connection is broken and then Cayenne auto- 
> reconnects,
> does it discard the PK cache?  (I'm guessing not, which could explain
> this.)
>
>
> -----Original Message-----
> From: Christian Mittendorf [mailto:christian.mittendorf@freenet.de]
> Sent: Thursday, July 13, 2006 6:23 AM
> To: cayenne-user@incubator.apache.org
> Subject: Re: Duplicate Key Problem
>
>
> I haven't found any hint to something abnormal in my log files yet.
> However, we experienced the duplicate key problem some minutes ago
> and I was able to track down the problem a bit.
>
> Affected is only one single WebApp and these "Duplicat entry" errors
> occured since yesterday, about 15:30. If I search for this exception
> I can find this ID list:
>
> $ cat x.log.2006-07-12 x.log | grep 'message from server'|uniq
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048820' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048821' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048822' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048823' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048824' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048825' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048826' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048827' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048828' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048829' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048830' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048831' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048832' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048833' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048834' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048835' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048836' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048837' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048836' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048838' for key 1"
> Caused by: java.sql.SQLException: null,  message from server:
> "Duplicate entry '17048839' for key 1"
>
> It seems as if one package of PKs (17048820 - 17048839 ) was double
> used.
> How does the PK magic of Cayenne work? Does each DataContext get its
> own set of IDs?
>
>
> Christian
>
>
>
> Am 12.07.2006 um 23:40 schrieb Andrus Adamchik:
>
>> Hmm.. MySQLPkGenerator runs "UNLOCK" in the finally block. Of
>> course if the connection goes down or something else equally bad
>> happens during unlock, then you can end up locking the table. I'll
>> be curious to know what exactly happened, as we may improve the
>> unlock reliability as a result.
>>
>> Andrus
>>
>>
>> On Jul 12, 2006, at 5:29 PM, Christian Mittendorf wrote:
>>
>>> Yes, all of our applications on this database are cayenne based.
>>> I will have a look at the logs tomorrow and see if I can find some
>>> other exceptions...
>>>
>>> Thanks,
>>> Christian
>>>
>>> Am 12.07.2006 um 19:56 schrieb Gentry, Michael ((Contractor)):
>>>
>>>> These could be related, then.  I know the MySQL adapter has to
>>>> lock the
>>>> auto_pk_support table to generate keys and perhaps something
>>>> happened to
>>>> leave the table locked.  Did you see any other exceptions?
>>>>
>>>> Also, you said you have multiple applications hitting the same
>>>> database.
>>>> Are all of these applications Cayenne-based?
>>>>
>>>> Thanks,
>>>>
>>>> /dev/mrg
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: Christian Mittendorf [mailto:christian.mittendorf@freenet.de]
>>>> Sent: Wednesday, July 12, 2006 1:50 PM
>>>> To: cayenne-user@incubator.apache.org
>>>> Subject: Re: Duplicate Key Problem
>>>>
>>>>
>>>> We don't use the autoincrement from MySQL.
>>>>
>>>> Am 12.07.2006 um 16:35 schrieb Gentry, Michael ((Contractor)):
>>>>
>>>>> Are you using MySQL's autoincrement feature for the PKs or the
>>>>> auto_pk_support table from Cayenne?
>>>>>
>>>>> -----Original Message-----
>>>>> From: Christian Mittendorf  
>>>>> [mailto:christian.mittendorf@freenet.de]
>>>>> Sent: Wednesday, July 12, 2006 4:29 AM
>>>>> To: cayenne-user@incubator.apache.org
>>>>> Subject: Duplicate Key Problem
>>>>>
>>>>>
>>>>> Hello!
>>>>>
>>>>> We are running a MySQL 5.0 server using InnoDB tables for our
>>>>> applications. We have multiple web applications accessing this  
>>>>> same
>>>>> database and the system is running smooth and without problems
>>>>> (almost).
>>>>>
>>>>> But yesterday we were experiencing some strange errors. During the
>>>>> afternoon some CayenneRuntimeExceptions appeared in the log file,
>>>>> which were caused by:
>>>>>
>>>>> Caused by: java.sql.SQLException: null,  message from server:
>>>>> "Duplicate entry '4353880' for key 1"
>>>>>
>>>>> A bit later other CayenneRuntimeException appeared. For those
>>>>> exceptions the cause was:
>>>>>
>>>>> Caused by: java.sql.SQLException: Deadlock found when trying to  
>>>>> get
>>>>> lock; Try restarting transaction,  message from server: "Lock wait
>>>>> timeout exceeded; try restarting transaction"
>>>>>
>>>>> I'm now wondering, are both errors related to each other?
>>>>>
>>>>> There are, from my point of view, two possible causes for the
>>>>> "Duplicate entry..." message:
>>>>>
>>>>> - two Insert statements on the same object, which might be  
>>>>> possible
>>>>> if the application is clustered, which our applications are  
>>>>> not, or
>>>>> - dual use of the same key in different objects
>>>>>
>>>>> Has anybody else experienced something like that? Are there any
>>>>> hints
>>>>> what I might do to avoid such situations?
>>>>>
>>>>> Christian
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>

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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