This is a bit surprise when we encountered a case where InnoDB is not releasing its row lock when there is an error condition within the transaction. And I verified with Falcon, Oracle, SQL Server and Sybase; all seemed to work as expected.

For example; just open a transaction in a session and execute a error statement (lets say duplicate key) and on the other new session try to get a row lock on the same record (use where clause with FOR UPDATE) and you will notice that InnoDB blocks on this statement until you issue a explicit rollback or commit. But remember there is nothing happened on the first session other than duplicate error on that row. So, InnoDB should implicitly unlock the row when there is an error; and looks like it is not doing that.

Here is the scenario:

First create a single column table and populate some rows (lets say 20 rows in this case) on any version of MySQL/InnoDB.

mysql> create table …