23.7.1.3 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 Log 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 Change Log). 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 Change Log.
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 Change Logs and VC).