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.mittendor..reenet.de]
Sent: Thursday, July 13, 2006 6:23 AM
To: cayenne-use..ncubator.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.mittendor..reenet.de]
>>> Sent: Wednesday, July 12, 2006 1:50 PM
>>> To: cayenne-use..ncubator.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.mittendor..reenet.de]
>>>> Sent: Wednesday, July 12, 2006 4:29 AM
>>>> To: cayenne-use..ncubator.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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