Skip to content

Explain brotli choice and compression agility #501

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
extiop merged 1 commit into from
Mar 17, 2026
Merged

Explain brotli choice and compression agility #501

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 6 additions & 0 deletions doc/src/FORMAT.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,12 @@ The inner layer, is split in `4 * 1024 * 1024`-bytes chunks, except for the last

The compression layer footer information can be retrieved by first reading the value of `sizes_info.tail_length` at the end of the layer, then reading the preceding `sizes_info.tail_length`-bytes.

#### Why Brotli?

Brotli is used for the compression layer as it offers a very good trade-off between compression ratio and CPU cost, is widely adopted, and has mature open-source implementations. Choosing a single, well-known algorithm reduces interoperability and maintenance costs.

If another compression algorithm is desired, data can be compressed by third-party means and put in MLA entries with Brotli compression layer disabled (e.g. compress files then use `mlar create --uncompressed` or use a compressor implementing `Read` with `ArchiveWriter` API). If another compression algorithm was to be integrated at the format level in the future, a new version of the format would be needed.

### MLA entries stream

The layer `entries_layer_magic` ASCII magic is "MLAENAAA".
Expand Down
Loading