The Source Integrity Professional Edition User Guide - MKS

Understanding Source Integrity
Storing Deltas
When Source Integrity performs a check-in operation, it calculates
and stores the delta between the new revision and the previous one in
the archive.
For instance, in the situation described earlier, revision 1.1 (that is, the
first revision checked in) now contains a complete description of the
changes that must be made to revision 1.2 to rebuild revision 1.1. This
list of changes, the delta, is the key to understanding how archives
store revisions and rebuild working files on demand.
To check out revision 1.1, Source Integrity
reads the list of differences (that is, the delta) it contains
applies the changes to revision 1.2., rebuilding a duplicate of the
original revision 1.1
copies the revision to a working file
Using this technique, Source Integrity can recreate any revision
without having to store complete copies. Usually, if you save only the
changed portion of each revision, the archive will be much smaller
than if the entire file were saved each time. There are situations when
this may not be the case; if you are storing binary files in an archive, a
complete copy of each revision is stored by default (see “Storing
Entire File” next).
When Source Integrity compares the file being checked in to the
preceding revision in the archive, it compares the two files line by
line. While this is a logical—and efficient—way to handle text files, it
is not always effective with binary files, since a relatively small
change at the beginning of a binary file can displace all subsequent
characters in the file, cascading changes through all remaining lines.
As a consequence, the record of changes (that is, the delta) for some
binary files may be as large as, or larger than, the file itself. For this
reason, Source Integrity provides a number of configurable
techniques for checking in files.
Storing Changes Only
With this method, Source Integrity calculates and stores a delta for
each revision of a file when it is checked in. This is the default and
recommended method for checking in text files. You can use this
method for storing binary files, but MKS does not recommend it.
16 Source Integrity Professional Edition