23.8.1.3 Types of Log File

Projects that use a revision control system can have two types of log for changes. One is the per-file log maintained by the revision control system: each time you check in a change, you must fill out a log entry for the change (see section Features of the Log Entry Buffer). This kind of log is called the version control log, also the revision control log, RCS log, or CVS log.

The other kind of log is the file ‘ChangeLog’ (see section Change Logs). It provides a chronological record of all changes to a large portion of a program—typically one directory and its subdirectories. A small program would use one ‘ChangeLog’ file; a large program may well merit a ‘ChangeLog’ file in each major directory. See section Change Logs.

A project maintained with version control can use just the per-file log, or it can use both kinds of logs. It can handle some files one way and some files the other way. Each project has its policy, which you should follow.

When the policy is to use both, you typically want to write an entry for each change just once, then put it into both logs. You can write the entry in ‘ChangeLog’, then copy it to the log buffer when you check in the change. Or you can write the entry in the log buffer while checking in the change, and later use the C-x v a command to copy it to ‘ChangeLog’ (see section Change Logs and VC).