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DBMS_LOCK.ALLOCATE_UNIQUE - ALLOCATE_UNIQUE_AUTONOMOUS

dbms_lock.allocate_unique writes (insert) or updates (update) the/a corresponding entry in dbms_lock_allocated and then commits the session.
allocate_unique_autonomous is the same as allocate_unique except that it performs the modification in dbms_lock_allocated in an autonomous transaction.

See also

These procedures clean up dbms_lock_allocated at every 100th attempt to to create an entry into that table.
dbms_lock

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Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:51 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(51): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(66): id_of(Object(PDO), 'uri', '/notes/developm...') #2 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/developm...', 1788554728, '216.73.216.30', 'Mozilla/5.0 App...', NULL) #3 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/development/databases/Oracle/installed/packages/dbms/lock/api/allocate_unique(42): insert_webrequest() #4 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 51