The Exadata Storage Server provides a unique compression capability called Hybrid Columnar Compression (HCC) that enables dramatic reductions in storage for large databases. Hybrid Columnar Compression technology is an innovative method of organizing data within a database table that uses a combination of both row and columnar methods for storing data. This hybrid approach achieves the compression benefits of columnar storage, while avoiding the performance shortfalls of a pure columnar format.
With Hybrid Columnar Compression, Exadata enables the highest levels of data compression possible with Oracle databases, and provides substantial cost-savings and performance improvements due to reduced I/O, especially for analytic workloads. Storage savings is data-dependent and often ranges from 5x to 20x. Average storage savings is an industry-leading 10x. On conventional systems, enabling high data compression has the drawback of reducing performance as it adds the load of decompression to the CPU. Because the Exadata Database Machine is able to offload decompression to processors in Exadata storage, and in addition there is reduced I/O need because of the high compression achieved, most analytic workloads run faster using Hybrid Columnar Compression than without it.
Two modes of Hybrid Columnar Compression are available. Warehouse compression mode is suitable for read-intensive workloads and provides large storage savings and enhanced analytic performance. Archive compression mode provides the highest degree of compression and is targeted at data that is seldom accessed but still must be kept online. In addition, this data can now be seamlessly stored on the XT storage server for further cost reduction.
On OLTP systems, Hybrid Columnar Compression can be used to compress older, less active data while newer, more active and update-intensive data can be compressed using Advanced Row Compression. Oracle Database Release 18c and above provides the ability to change the type of compression used by individual table partitions online (even if there are global indexes on the table), to ensure seamless tiering across different compression types as data ages and becomes less active.
For data analytics, Exadata Smart flash Cache implements a unique algorithm to accelerate reporting and analytical queries, called Exadata Columnar Flash Cache. Columnar flash Caching implements a dual format architecture in Exadata flash by automatically transforming frequently scanned Hybrid Columnar Compressed data into a pure columnar format as it is loaded into the flash cache. Smart scans on pure columnar data in flash run faster because they read only the selected columns, reducing flash I/Os and storage server CPU consumption. This accelerates reporting and analytic queries while maintaining excellent performance for OLTP-style single row lookups.