However in step 6, when session C tries to get hold of another 700 (tickets), we finally run into a limitation: a Check Constraint violation. Still no row lock preventing session C from making the update. This update is accepted – again while both sessions A and B have made their own claims on that ticket capacity. Step 5 in session C reduces the capacity by another 500 – although a query for the current capacity in that session would also return the original 2000. Step 4 in session B selects the current capacity and finds that the value in column capacity is still at the original 2000 despite the update in session B just prior to this query that took 800 from that capacity. When I introduce a third session and perform two more updates, you will see that the these transactions are not isolated from each other. However, this example shows that in release 23c it can lock even less than a single record. Some databases lock a table or a page (set of records) but from its incarnation, Oracle Database has always been very fine grained by only locking the row in question. The traditional behavior of the Oracle Database is to lock a row as soon as it is updated. It can perform the update, almost as if session 1 does not exist. and is able to! It does not run into a lock. ![]() Session 2 tries to update that same record …. Session 1 performs an update on this record. ![]() Session 1 inserts a record and commits it. Subsequent calls to ALLOCATE_UNIQUE_AUTONOMOUS may delete expired locks to recover space.This should surprise if not baffle you. You should not delete locks from this table. Number of seconds to wait after the last ALLOCATE_UNIQUE_AUTONOMOUS has been performed on a specified lock, before permitting that lock to be deleted from the ALLOCATE_UNIQUE_AUTONOMOUS table. Therefore, do not pass lock handles from one session to another. Returns the handle to the lock ID generated by ALLOCATE_UNIQUE_AUTONOMOUS.Īll sessions using a lock handle returned by ALLOCATE_UNIQUE_AUTONOMOUS with the same lock name are referring to the same lock. Table 94-5 ALLOCATE_UNIQUE_AUTONOMOUS Procedure Parameters Parameter Subsequent calls to ALLOCATE_UNIQUE may delete expired locks to recover space. Number of seconds to wait after the last ALLOCATE_UNIQUE has been performed on a specified lock, before permitting that lock to be deleted from the DBMS_LOCK_ALLOCATED table. ![]() This provides better isolation between different applications that are using this package.Īll sessions using a lock handle returned by ALLOCATE_UNIQUE with the same lock name are referring to the same lock. You can use this handle in subsequent calls to REQUEST, CONVERT, and RELEASE.Ī handle is returned instead of the actual lock ID to reduce the chance that a programming error accidentally creates an incorrect, but valid, lock ID. Returns the handle to the lock ID generated by ALLOCATE_UNIQUE. Name of the lock for which you want to generate a unique ID.ĭo not use lock names beginning with ORA$ these are reserved for products supplied by Oracle. Table 94-4 ALLOCATE_UNIQUE Procedure Parameters Parameter
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