Which two statements are true about space-saving features in an Oracle Database? (Choose two.)
A. Private Temporary Tables (PTTS) store metadata in memory only
B. An index created with the UNUSABLE attribute has no segment
C. If they exist for a session, Private Temporary Tables (PTTs) are always dropped at the next COMMIT OR ROLLBACK statement
D. An index that is altered to be UNUSABLE will retain its segment
E. A table that is truncated will always have its segment removed
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AB
Answer: AB
Discussion: Refer 19c Database administrator I for detail under temporary tables
A is correct: A global temporary table definition is visible to all sessions. However, the content in the table is specific to a session. Global temporary table definitions are stored on disk. A private temporary table definition is visible only to the session that created it. The table definition is stored only in memory.
B is correct: When an unusable index is created, no segment is created
C is incorrect: There are two types of durations for private temporary tables: Transaction: The private temporary table is automatically dropped when the transaction in which it was created ends with either a ROLLBACK or COMMIT. This is the default behaviour if no ON COMMIT clause is defined at private temporary table creation. Session: The private temporary table is automatically dropped when the session that created it ends. This is the behaviour if the ON COMMIT PRESERVE DEFINITION clause is defined at the private temporary table creation.
D is incorrect: see B
E is incorrect: TRUNCATE TABLE statement: Deallocates all space used by the removed rows except that specified by the MINEXTENTS storage parameter