Row Versioning

Abstract

When data is stored in HBase, a version, also called a timestamp) is required for each value stored in a cell. The timestamp is created automatically by the RegionServer or may be supplied explicitly. By default, the timestamp is the time at the RegionServer when the data was written. Alternatively, the timestamp may be set explicitly. Timestamps are stored in descending order in an HFile, which implies the most recent timestamp is stored first. The timestamp identifies a version and must be unique for each cell. A {row, column, version} tuple specifies a cell in a table. A KeyValue consists of the key and a value with the key being comprised of the row key + column Family + column qualifier + timestamp, as shown in Figure 5-4. The value is the data identified by the key. The timestamp represents a particular version.