Understanding SYSTEM-VERSIONED and APPLICATION-VERSIONED Temporal Tables in MySQL: Exploring the Power of Historical Data Tracking

Introduction

Temporal tables in MySQL offer a powerful solution for tracking historical changes to data. They provide valuable insights into how records have evolved over time. With the introduction of SYSTEM-VERSIONED and APPLICATION-VERSIONED temporal tables, MySQL has enhanced its capabilities to manage temporal data effectively.

In this blog, we will dive into the internals of these temporal tables, exploring their implementation, use cases, and advantages. Understanding these features will empower database administrators and developers to make informed decisions when dealing with historical data. It also helps ensure data integrity and historical accuracy: SYSTEM-VERSIONED and APPLICATION-VERSIONED temporal tables.

1. SYSTEM-VERSIONED Temporal Tables:

   • SYSTEM-VERSIONED temporal tables are managed entirely by the MySQL server. They automatically maintain historical versions of data in a separate history table.
     
     
   • When you create a SYSTEM-VERSIONED temporal table, you define two tables. The first table stores the current data, and the second table keeps the historical versions.
     
     
   • The current data table contains the most recent version of the data. The history table stores all previous versions, along with timestamps indicating when each change occurred. 
     
     
   • When you update a row in the current data table, MySQL automatically inserts the old version of the row into the history table. It also records the timestamp of the change.  
     
     
   • Similarly, when you delete a row from the current data table, MySQL marks the row as deleted. At the same time, it inserts a copy of the row into the history table, preserving the deleted version. When you delete a row, MySQL marks it as deleted in the current table. It then moves a copy of the deleted row to the history table, preserving the record.
     
     
   • To retrieve historical data, you query both the current data table and the history table. Using the appropriate timestamp criteria helps you fetch the desired data version.

2. APPLICATION-VERSIONED Temporal Tables:

   • APPLICATION-VERSIONED temporal tables allow you to manage historical versions of data manually. Unlike SYSTEM-VERSIONED tables, there is no separate history table managed by the MySQL server.
     
     
   • When creating an APPLICATION-VERSIONED temporal table, you define two timestamp columns. One column records the valid time, and the other stores the transaction time.
     
     
   • The valid time represents the period when the data remains valid. The transaction time logs when the system inserts or updates the data.
     
     
   • Unlike SYSTEM-VERSIONED tables, the management of historical data in APPLICATION-VERSIONED tables is done explicitly by the application. When a row is updated, it is up to the application to decide how to handle the previous version of the data, whether to store it in a separate table or archive it in some other way.
     
     
   • Similarly, when querying historical data from an APPLICATION-VERSIONED table, the application needs to consider both the valid time and transaction time columns to retrieve the appropriate version of the data.

In summary, SYSTEM-VERSIONED temporal tables in MySQL automatically maintain historical records in a separate history table. In contrast, APPLICATION-VERSIONED temporal tables require the application to handle historical data manually. Both types help track changes over time and maintain historical records. They prove useful for auditing, compliance, and historical analysis.

Conclusion

Temporal tables in MySQL, including SYSTEM-VERSIONED and APPLICATION-VERSIONED variants, open up a new realm of possibilities for managing historical data. The ability to automatically track and manage changes over time allows organizations to gain deeper insights, audit data modifications, and meet compliance requirements effectively. By harnessing the power of these temporal tables, database administrators and developers can design more robust applications, safeguard data integrity, and ensure historical accuracy. Embracing temporal tables as part of a comprehensive data management strategy will undoubtedly pave the way for more data-driven and reliable systems, driving growth and success for businesses in today’s data-driven world.