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Oracle has introduced a hybrid column-oriented storage option for Exadata with the release of Oracle Database 11g Release 2.
Ever since Mike Stonebraker and fellow researchers at MIT, Brandeis University, the University of Massachusetts and Brown University presented (PDF) C-Store, a column-oriented database at the 31st VLDB Conference, in 2005, the database industry has debated the relative merits of row- and column-store databases.
While row-based databases dominated the operational database market, column-based database have made in-roads in the analytic database space, with Vertica (based on C-Store) as well as Sybase, Calpont, Infobright, Kickfire, Paraccel and SenSage pushing column-based data warehousing products based on the argument that column-based storage favors the write performance required for query processing.
The debate took a fresh twist recently as former SAP chief executive, Hasso Plattner, recently presented a paper (PDF) calling for the use of in-memory column-based storage databases for both analytical and transaction processing.
As interesting as that is in theory, of more immediate interest is the fact that Oracle – so often the target of column-based database vendors – has introduced a hybrid column-oriented storage option with the release of Oracle Database 11g Release 2.
As Curt Monash recently noted there are a couple of approaches emerging to hybrid row/column stores.
Oracle’s approach, as revealed in a white paper (PDF) has been to add new hybrid columnar compression capabilities in its Exadata Storage servers.
This approach maintains row-based storage in the Oracle Database itself while enabling the use of column-storage to improve compression rates in Exadata, claiming a compression ratio of up to 10 without any loss of query performance and up to 40 for historical data.
As Oracle’s Kevin Closson explains in a blog post: “The technology, available only with Exadata storage, is called Hybrid Columnar Compression. The word hybrid is important. Rows are still used. They are stored in an object called a Compression Unit. Compression Units can span multiple blocks. Like values are stored in the compression unit with metadata that maps back to the rows.”
Vertica took a different hybrid approach with the release of Vertica Database, 3.5, which introduced FlexStore, a new version of the column-store engine, including the ability to group a small number of columns or rows together to reduce input/output bottlenecks. Grouping can be done automatically based on data size (grouped rows can use up to 1MB) to improve query performance of whole rows or specified based on the nature of the column data (for example, bid, ask and date columns for a financial application) to improve query performance.
Likewise, the Ingres VectorWise project (previously mentioned here) will create a new storage engine for the Ingres Database positioned as a platform for data-warehouse and analytic workloads, make use of vectorized execution, which sees multiple instructions processed simultaneously. The Vectorwise architecture makes use of Partition Attributes Across (PAX), which similarly groups multiple rows into blocks to improve processing, while storing the data in columns.
Update – Daniel Abadi has provided an overview at the different approaches to hybrid row-column architectures and suggests something I had suspected, that Oracle is also using the PAX approach, except outside the core database, while Vertica is using what he calls a fine-grained hybrid approach. He also speculates that Microsoft may end up going the third route, fractured mirrors – Update
Perhaps the future of the database may not be row- or column-based, but plaid.