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 tableI was just looking at the MySQL docs for "LOCK TABLES" and it appears towork 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 betweenselect and update above. An application got 20 PKs, but the connectionwas 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/mrgPS. 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:[EMAIL PROTECTED] Sent: Thursday, July 13, 2006 6:23 AM To: [email protected] 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:[EMAIL PROTECTED] Sent: Wednesday, July 12, 2006 1:50 PM To: [email protected] 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:[EMAIL PROTECTED]Sent: Wednesday, July 12, 2006 4:29 AM To: [email protected] Subject: Duplicate Key Problem Hello! We are running a MySQL 5.0 server using InnoDB tables for ourapplications. We have multiple web applications accessing this samedatabase 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 getlock; 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:[EMAIL PROTECTED] P.S. A good JDO? O, Gasp!
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