SCU3 transaction is used to see the IMG change logs for modified objects.

If your table change log is not active, it will gives you a message that :-
...table logging is switched off... 

This particular setting can be changed in the following path :-
IMG--> Basis Components --> System Administration --> Tables changes recording

You can log changes made to the following tables:

- Control tables (system logic control) 
- Customizing tables 
What is recorded is always in the form of complete "before" images, that is, all entries as they appear before the changes.
The recorded data is compressed without buffering, and this is not an appropriate method for recording and managing large amounts of data. Activating logging impacts on performance as it entails twice as many database updates as would otherwise be the case, and the database storage load is also increased substantially.

It is recommend that you use logging for your production clients and Customizing clients so that you can see exactly where Customizing tables have been changed. Other than the reasons above, it is not recommended that you use this tool for application tables.

Two conditions have to be met for a table to be logged:

1. The table has to be selected for logging in the Dictionary (see Dictionary -> Table maintenance -> Technical configuration).

2. Logging also has to be set in the system profile
Set the rec/client (note the use of lowercase characters) profile parameter to one of the following values :-
- OFF: no logging at all (effectively a central system switch) 
- nnn: logs client-specific tables in client nnn only 
- mmm,nnn,ppp,...: logs client-specific tables in the named clients 
- ALL: logs all client-specific tables in all clients. 

Caution: Only in exceptional circumstances is it appropriate to use the 'ALL' setting. If, for example, the profile parameter is set to 'ALL' when you upgrade all test clients (including 000, the SAP client), these changes are recorded in the system log file. This reduces performance and requires a lot of database space.

The default setting is OFF (no changes are logged).

If logging is set in the ABAP Dictionary, changes to client-indepedent tables are always logged unless rec/client is set to 'OFF'

Use the ABAP programs RSTBHIST or RSVTPROT to analyze table changes. RSVTPROT allows you to analyze change logs both at table level and with reference to Customizing objects. To access the program, select an executable Customizing activity in IMG and choose Goto -> Change log. 

Questions
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