---
title: "How DB2 Keeps Logs for Changes to Tables"
description: "When changes are made to the data in tables, subsequently changing the table space and index spaces, DB2 writes one or more records to its log so that a blackout of the changes can be performed if the..."
url: https://srinimf.com/2015/09/17/how-logging-happens-in-db2-when-createinsert-and-delete/
date: 2015-09-17
modified: 2026-10-10
author: "Srini"
image: https://i0.wp.com/srinimf.com/wp-content/uploads/2015/09/pexels-photo-3756168.jpeg?fit=1880%2C1253&ssl=1
categories: ["DB2"]
tags: ["DB2 Logging tips"]
type: post
lang: en
---

# How DB2 Keeps Logs for Changes to Tables

When changes are made to the data in tables, subsequently changing the table space and index spaces, [DB2 writes](http://www.indeed.com/jobs?q=Mainframe&indpubnum=6634974704162507)one or more records to its log so that a blackout of the changes can be performed if the unit of work fails. DB2 can also use this information to reapply changes that may have been lost when recovering to a previous point in time.

Related[Logging in IMS DB: A Complete Guide to Audit Trail Records](https://srinimf.com/2016/09/30/3-strong-reasons-why-logging-in-ims-db-needed/)

## The primary purpose of the active log is to record all changes—inserts, updates, and deletes—made to DB2 objects.

- **The DML statements are recorded in the log as follows:**
  - INSERT: Entire after-image of the record is logged; called a redo record
  - DELETE: The before-image is recorded; called an undo record
  - UPDATE: Both the before and after images—undo and redo record—are recorded

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## Log Entries

**Each log record has its own unique identifier.** In a parallel sysplex DB2 data sharing environment, it is known as the LRSN (log record sequence number). When you are operating in a non-data sharing environment, this number is known as the log RBA, or the offset of the record in the log from the beginning of the log. In a data sharing environment, the **LRSN helps** to track the sequence of events that happen over multiple members in the data sharing group.

Each member has its own log; if multiple members are making updates to the same data, the logs must be merged during a recovery. Because the LRSN is unique across the sysplex, this type of merging is possible.

*Related:* [Data warehousing and Teradata basics](http://click.linksynergy.com/link?id=yYOcxCqEbGo&offerid=323058.250310&type=2&murl=https%3A%2F%2Fwww.udemy.com%2Fintroduction-to-data-warehouse-and-teradata-basics%2F)

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