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From Christian Mittendorf <christian.mittend...@freenet.de>
Subject Re: Duplicate Key Problem
Date Thu, 13 Jul 2006 16:50:20 GMT

Am 13.07.2006 um 15:17 schrieb Gentry, Michael ((Contractor)):

> I was just looking at the MySQL docs for "LOCK TABLES" and it  
> appears to
> work differently with InnoDB.

http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html

Yes, it seems to behave differently and I think that our DB is
running with AUTOCOMMIT=1, which is the default setting:

"The correct way to use LOCK TABLES with transactional tables,
such as InnoDB tables, is to set AUTOCOMMIT = 0 and not to call
UNLOCK TABLES until you commit the transaction explicitly."


> Which DB storage type are you using?

We are using InnoDB...


> 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.

The db has collected 3893813 connection attempts and 534 aborted clients
since we restarted the db two days ago. However, there are also other
databases that are hosted on that mysql server that are accessed with  
perl
or php clients.


> Any chance you can use PostgreSQL?  It uses sequences which are atomic
> operations.

Well.. migrating to PostgreSQL is no solution right now because  
knowledge
is primarily focussed on MySQL yet. However, there are some colleages
where PostgreSQL is in use.

Christian


>
> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>


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