Fossil

The bulk of the repository database (typically 75 to 85%) consists
of the artifacts that comprise the
[./fileformat.wiki | enduring, global, shared state] of the project.
The artifacts are stored as BLOBs, compressed using
[http://www.zlib.net/ | zlib compression] and, where applicable,
using [./delta_encoder_algorithm.wiki | delta compression].
The combination of zlib and delta compression results in a considerable
space savings.  For the SQLite project (when this paragraph was last
updated on 2020-02-08)
the total size of all artifacts is over 7.1 GB but thanks to the
combined zlib and delta compression, that content only takes less than
97 MB of space in the repository database, for a compression ratio
of about 74:1.  The median size of all content BLOBs after delta
and zlib compression have been applied is 156 bytes.
The median size of BLOBs without compression is 45,312 bytes.

Note that the zlib and delta compression is not an inherent part of the
Fossil file format; it is just an optimization.
The enduring file format for Fossil is the unordered
set of artifacts. The compression techniques are just a detail of
how the current implementation of Fossil happens to store these artifacts
efficiently on disk.

All of the original uncompressed and un-delta'd artifacts can be extracted
from a Fossil repository database using
the [/help/deconstruct | fossil deconstruct]
command. Individual artifacts can be extracted using the
[/help/artifact | fossil artifact] command.
When accessing the repository database using raw SQL and the
[/help/sqlite3 | fossil sql] command, the extension function
"<tt>content()</tt>" with a single argument which is the SHA1 or
SHA3-256 hash
of an artifact will return the complete uncompressed
content of that artifact.

Going the other way, the [/help/reconstruct | fossil reconstruct]
command will scan a directory hierarchy and add all files found to
a new repository database.  The [/help/import | fossil import] command
works by reading the input git-fast-export stream and using it to construct
corresponding artifacts which are then written into the repository database.