At 12:54 PM 2/10/2006, Mark Matthews wrote:
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Patrick Duda wrote:
> I guess I don't understand this locking stuff. I have a InnoDB table
> that has one thing in it, a counter. All I want to do is have multiple
> instances of the code read this counter and increment it. I want to
> make sure that each one is unique.
>
> Here is what I am doing in java:
>
> c.setAutoCommit(false);
> ...
> rs = statement.executeQuery("select request_id from requestid_innodb for
> update");
> ...
> String updateQuery = "update requestid_innodb set request_id=";
> updateQuery = updateQuery + nextRequestId;
> tempStatement = c.createStatement();
> tempStatement.executeUpdate(updateQuery);
> ...
> c.commit();
> c.setAutoCommit(true);
>
> If I have multiple instances of this code running I end up with
> duplicate keys. I thought this was suppose to lock the table so that
> would not happen.
>
> What am I not doing right? What am I not understanding about locking?
>
> Thanks
>
> Patrick
>
>
Patrick,
Are you sure the table is using the InnoDB storage engine? What does the
output of "SHOW CREATE TABLE " for the table in question say?
-Mark
ysql> show create table requestid_innodb;
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create
Table
|
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------+
| requestid_innodb | CREATE TABLE `requestid_innodb` (
`request_id` int(11) NOT NULL default '0',
PRIMARY KEY (`request_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
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