Hybrid Columnar Compression

10.7.2 Hybrid Columnar Compression

Exadata Hybrid Columnar Compression offers higher compression levels for direct path loaded data. This new compression capability is recommended for data that is not updated frequently. You can specify Hybrid Columnar Compression at the partition, table, and tablespace level. You can also specify the desired level of compression, to achieve the proper trade-off between disk usage and CPU overhead. Included is a compression advisor that helps you determine the proper compression levels for your application.

This feature allows the database to reduce the number of I/Os to scan a table. For example, if you compress data 10 to 1, then the I/Os are reduced 10 to 1 as well. In addition, Hybrid Columnar Compression saves disk space by the same amount.

This feature also allows the database to offload Smart Scans for a column-compressed table to Oracle Exadata Storage Servers. When a scan is done on a compressed table, Oracle Exadata Storage Server reads the compressed blocks from the disks for the scan. Oracle Exadata System Software then decompresses the referenced columns, does predicate evaluation of the data, and applies the filter. The storage server then sends back qualifying data in an uncompressed format. Without this offload, data decompression would take place on the database server. Having Oracle Exadata Storage Server decompress the data results in significant CPU savings on the database server.