What is Journaling on IBM i?

Learning Objective

By the end of this lesson, you will be able to explain what journaling is and what kind of record it keeps of changes to a table.

Simple Explanation

Every physical file or table covered earlier in this course simply holds its current data: whatever the last WRITE, UPDATE, or DELETE left behind, with no memory of what came before. Journaling adds a separate, ongoing record of every change made to a journaled object, capturing what changed, when, and by which job, independent of the table's own current contents.

STRJRNPF FILE(MYLIB/CUSTMAST) JRN(MYLIB/CUSTJRN)

Once a table like CUSTMAST is journaled this way, every insert, update, and delete against it is also recorded as a separate journal entry, in addition to the change itself being applied to the table as usual.

Why It Matters

Without journaling, once a change happens, such as a customer's credit limit being updated, the previous value is simply gone from the table itself. Journaling keeps a running history of changes alongside the table's current data, which is what makes recovery, auditing, and commitment control, all covered later in this batch, possible in the first place.

Practical Example

Recall CUSTMAST from earlier in this course. Without journaling, an accidental UPDATE that changed every customer's credit limit to zero would leave no record of what the correct values used to be, beyond whatever backup happens to exist. With CUSTMAST journaled, the journal entries recorded before that mistaken update contain the actual prior values, which is exactly the kind of information journaling exists to preserve.

This is a simplified, illustrative example rather than a specific real incident, but it reflects exactly why journaling matters.

Common Confusions

"Is journaling the same thing as making a backup?" No. A backup is a snapshot taken at one point in time. Journaling records every individual change continuously as it happens, which is a different, complementary kind of protection.

"Does journaling change what a normal READ or CHAIN operation returns?" No. Reading a journaled table still returns its current data exactly as before; journaling adds a separate record of changes alongside the table, without changing how normal file operations behave.

"Does every table need to be journaled?" Not necessarily. Journaling is most valuable for tables where the history of changes genuinely matters, for recovery, auditing, or commitment control, covered later in this batch, rather than being a requirement for every table on the system.

Quick Recap

• Journaling keeps an ongoing record of every change made to a journaled table, independent of the table's own current contents.
• STRJRNPF is the command that starts journaling a physical file against a journal.
• Journaling does not change how normal read or write operations work; it adds a separate record alongside them.
• Journaling is the foundation that makes recovery, auditing, and commitment control, all covered later in this batch, possible.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "Can you give me another realistic example of why having a record of past changes, not just current data, would matter?"
• "Why might a shop choose to journal some tables but not others?"