Glossary

Coherence - Oracle Coherence is a distributed memory cache for applications. Coherence replicates data from one to another ensuring availablity of data.

Column - an attribute of a table. A column is also frequently referred to as a field.

Columnar Database - See Columnar Storage.

Columnar Storage - Columnar storage in a database refers to a database that stores data in columns instead of rows. In some columnar storage engines, it also means that data is compressed in columns allowing much greater compression that data stored across rows (as columnar data is more likely to have duplicate values). Columnar storage is available in Sybase IQ, Vertica, Paraccel, and LucidDB amongst others. More and more are coming on the scene daily.

Some columnar storage engines are set up through indexing schemes such as B-Tree and Bitmaps. Other storage engines actually place data on disk in matching, row based locations allowing one to skip the issues that come with multiple indexes. Some columnar database also store duplicate versions of the data, pre-sorted in various orders to allow faster retrieval.