Autonomous transactions are important because
they can commit work without destroying the context of the larger
transaction.
78 | Chapter 3: Installing and Running Oracle
Commit or rollback
Once a user enters the data for his transaction, he can either commit the transaction
to make the changes permanent or roll back the transaction to undo the
changes.
System Change Number (SCN)
A key factor in preserving database integrity is an awareness of which transaction
came first. For example, if Oracle is to prevent a later transaction from
unwittingly overwriting an earlier transaction??™s changes, it must know which
transaction began first. The mechanism Oracle uses is the System Change Number,
a logical timestamp used to track the order in which events occurred. Oracle
also uses the SCN to implement multiversion read consistency, which is
described in detail in Chapter 8.
Rollback segments
Rollback segments are structures in the Oracle database used to store ???undo???
information for transactions, in case of rollback. This undo information restores
database blocks to the state they were in before the transaction in question
started.
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