Locks are typically held by a transaction until it completes. This behavior prevents other transactions from making changes that would make it impossible to roll back the original transaction. At isolation level three, all locks must be held until a transaction ends to guarantee transaction serializability.
The only locks that are not held until the end of a transaction are cursor stability locks. These row locks are held for as long as the row in question is the current row of a cursor. In most cases, this amount of time is shorter than the lifetime of the transaction, but for WITH HOLD cursors, cursor stability locks can be held for the lifetime of the connection.
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