Auto Increment Primary ID inserting random values Today I was asked to look into this problem and I have never seen anything like this before. A table in our MySQL database, with a primary IDs column, which is set to autoincrement int, had some weird IDs. So the sequence goes as follows:



Some more random ids



You can see between 27243 and 27245, and 27324 and 27325 there are some different numbers inserted. This has caused a lot of problem for us since there are FK in another table which are now missing or messed up. Even today, there was one similar incidence.

In my many years of dealing with MySQL, this is the first time ever I am seeing something like this. What could have been the reason and how to correct it?

There are no triggers. Currently table create statement shows:

CREATE TABLE `txn` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`client_id` int(11) DEFAULT NULL,
`timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=27368 DEFAULT CHARSET=latin1;


Thanks.
I'm having a very difficult time thinking of any possible misbehaving mechanism inside MySQL or InnoDB that could cause this behavior as the result of a bug, without throwing errors or causing a crash.  It seems much more likely that the table is being updated by the application.  Instead of writing new rows, something is finding and updating old ones.

If that's not supposed to be happening, I would put a trigger on this table to block those updates.

mysql&gt; CREATE TRIGGER txn_bu BEFORE UPDATE ON txn FOR EACH ROW 
       SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'this table does not support updates';
Query OK, 0 rows affected (0.14 sec)

mysql&gt; UPDATE txn SET `timestamp` = NOW() WHERE id = 1;
ERROR 1644 (45000): this table does not support updates

mysql&gt;


This makes directly updating rows impossible.  Note that you don't need the usual DELIMITER change and BEGIN/END blocks because the trigger is comprised of a single simple statement.

If the table is never updated then the trigger would never fire, so there's no significant overhead associated with having it defined.  If it sees an update query then it's going to throw an exception back to the application which should generate exception reports or support tickets.  Arguably, if your application has a defect that's stomping data, you want it to fail hard, instead of soft.