Data Guard compresses data:

Data Guard compresses data:

A.
Always

B.
When using logical standby

C.
When using physical standby

D.
When catching up after a network failure

Explanation:
A Physical standby database replicates the exact contents of its primary database
across the Oracle Net network layer. While the physical storage locations can be different, the
data in the database will be exactly the same as the primary database.
Incorrect answer:
A, B: Logical standby databases convert the redo generated at the Primary database into data and
SQL and then re-apply those SQL transactions on the Logical standby, thus physical structures
and organization will be different from the Primary database. Users can read from logical standby
databases while the changes are being applied and, if the GUARD is set to STANDBY (ALTER
DATABASE GUARD STANDBY;), write to tables in the Logical standby database that are not
being maintained by SQL Apply.
Unfortunately there are a number of unsupported objects (ie: tables or sequences owned by
SYS, tables that use table compression, tables that underlie a materialized view or Global
temporary tables (GTTs)) and unsupported data types (ie: Datatypes BFILE, ROWID, and
UROWID, user-defined TYPEs, Multimedia data types like Oracle Spatial, ORDDICOM, and
Oracle Text Collections (e.g. nested tables, VARRAYs), SecureFile LOBs, OBJECT RELATIONAL
XMLTypes and BINARY XML).[2] Physical standby may be appropriate in such a case.