ORACLE 12C : Advanced Index compression

Oracle 12c rel.1 (12.1.0.2) introduced a new method for index compression called “advanced index compression” which is more effective in index compression than available methods in Oracle 11g .
Creating an index using advanced index compression reduces the size of unique and non-unique indexes.
Advanced index compression improves the compression ratios significantly .
Advanced Index Compression is not supported for bitmap indexes and for indexes on unique single-column indexes.
For a partitioned index, you can specify the compression type on a partition .
You can also specify advanced index compression on index partitions even when the parent index is not compressed.
Executing a CREATE INDEX DDL statement a block is filled with rows.
When it is full, it is compressed if enough space is saved to insert the next row.
When DML statements or other types of DDL statements are executed, and a block becomes full and is about to be split, the block might be recompressed.
The following statement enables advanced index compression:
CREATE INDEX aet.index_1 ON aet.blog (cp1, cp2)
COMPRESS ADVANCED LOW;
You can also specify the COMPRESS ADVANCED LOW clause during an index
rebuild .
Information about the index compression can be found in the data dictionary
views :
 ALL_INDEXES
 ALL_IND_PARTITIONS
 ALL_IND_SUBPARTITIONS