500: Lock request timeout 

Explanation:

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                            a.      The lock request or an implicit lock conflicts with the locks of another user. The maximum waiting time for being granted the lock has elapsed (special database parameter REQUEST_TIMEOUT).

                            b.      The database instance could not be stopped in a certain time interval, because transactions with SQL statements for data modification are still open.

User Response:

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                            a.      In some cases, the error message contains a more detailed description of the error. The lock request can be reissued. To avoid possible deadlock situations, it is advisable to roll back the transaction using a ROLLBACK statement.

                            b.      These prevent you having to stop the database instance.