Fetching of data from database while updating data
Therefore, control of data concurrency and data consistency is vital in a multiuser database. The serializable mode of transaction behavior tries to ensure that transactions run in such a way that they appear to be executed one at a time, or serially, rather than concurrently.
While this degree of isolation between transactions is generally desirable, running many applications in this mode can seriously compromise application throughput.
As a query enters the execution stage, the current system change number (SCN) is determined.
RAC does this using high speed, low latency interconnects to satisfy remote requests for data blocks. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began.For example, a function could access a table whose data is changed and committed by another user.For each execution of the When a transaction runs in serializable mode, all data accesses reflect the state of the database as of the time the transaction began.Oracle offers two isolation levels, providing application developers with operational modes that preserve consistency and provide high performance.The ANSI/ISO SQL standard (SQL92) defines four levels of transaction isolation with differing degrees of impact on transaction processing throughput.