Starting with Oracle Database 12c Release 1 (12.1.0.2), advanced index compression improves on traditional prefix compression for supported indexes on heap-organized tables.
Benefits of Advanced Index Compression
Prefix compression has limitations for types of indexes supported, compression ratio, and ease of use. Unlike prefix compression, which uses fixed duplicate key elimination for every block, advanced index compression uses adaptive duplicate key elimination on a per-block basis. The main advantages of advanced index compression are:
- The database automatically chooses the best compression for each block, using a number of internal algorithms such as intra-column level prefixes, duplicate key elimination, and rowid compression. Unlike in prefix compression, advanced index compression does not require the user to know data characteristics.
it support - Advanced compression works on both non-unique and unique indexes. Prefix compression works well on some non-unique indexes, but the ratios are lower on indexes whose leading columns do not have many repeats.
- The compressed index is usable in the same way as an uncompressed index. The index supports the same access paths: unique key lookups, range scans, and fast full scans.
- Indexes can inherit advanced compression from a parent table or containing tablespace.
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