Understand the Cassandra data model
The Cassandra data model defines
- Column family as a way to store and organize data
- Table as a two-dimensional view of a multi-dimensional column family
- Operations on tables using the Cassandra Query Language (CQL)
Cassandra1.2+reliesonCQLschema,concepts,andterminology, though the older Thrift API remains available
| Table (CQL API terms) | Column Family (Thrift API terms) |
|---|---|
| Table is a set of partitions | Column family is a set of rows |
| Partition may be single or multiple row | Row may be skinny or wide |
| Partition key uniquely identifies a partition, and may be simple or composite | Row key uniquely identifies a row, and may be simple or composite |
| Column uniquely identifies a cell in a partition, and may be regular or clustering | Column key uniquely identies a cell in a row, and may be simple or composite |
| Primary key is comprised of a partition key plus clustering columns, if any, and uniquely identifies a row in both its partition and table |
Row (Partition)
Row is the smallest unit that stores related data in Cassandra
- Rows: individual rows constitute a column family
- Row key: uniquely identifies a row in a column family
- Row: stores pairs of column keys and column values
- Column key: uniquely identifies a column value in a row
- Column value: stores one value or a collection of values
Rows may be described as skinny or wide
- Skinny row: has a fixed, relatively small number of column keys
- Wide row: has a relatively large number of column keys (hundreds or thousands); this number may increase as new data values are inserted
Key (Partition Key)
Composite row key
multiple components separated by colon
Composite column key
multiple components separated by colon
Column family (Table)
set of rows with a similar structure
Table with single-row partitions
Table with multi-row partitions
