Table Clusters

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Last updated: Aug 02, 2023
2 min read

A table cluster (also known as a clustered table) is a data storage mechanism that physically organizes related tables together on the disk. A table cluster is a feature found in some database management systems (DBMS) that allows multiple tables with similar structures and common columns to be stored in the same data blocks on disk. The primary objective of using a table cluster is to improve data retrieval efficiency by reducing I/O operations when accessing related data.

 

Here are the key characteristics and concepts related to table clusters:

  1. Common Columns: Tables in a cluster share common columns that are used as the cluster key. These columns have the same data type and often serve as the primary key or another important attribute used for joining related data.

  2. Single Data Block: Tables within a cluster are stored in a single data block on disk. This means that the data for multiple related tables is physically located close to each other, reducing the need for multiple disk reads during certain queries.

  3. Reduced I/O Operations: When a query involves data from multiple tables in a cluster, the DBMS can read the entire block containing the cluster's data, reducing the number of I/O operations compared to accessing each table separately.

  4. Indexing: Table clusters are usually supported by a cluster index, which is a type of index that organizes the data in a way that matches the physical layout of the clustered tables. The cluster index helps to locate the cluster block efficiently.

  5. Join Performance: Table clusters are especially beneficial for queries involving joins on the common columns of related tables. Joining clustered tables can be more efficient due to their physical proximity on disk.

It's important to note that not all database systems support table clusters, and their use may vary based on the specific workload and access patterns of the application. Table clustering can be helpful for scenarios where related data is frequently accessed together, but it might not be the best approach for all situations. Modern database systems often provide various indexing and data organization options, and database administrators must carefully consider the trade-offs and choose the most suitable data storage and indexing strategies based on the application's requirements and query patterns.