Support for the Go implementation of CartoCSS (Magnacarto) for Kosmtik. This implementation is available as a native extension for Node.js. Currently the native extension is available for Linux and MacOS X systems only and is still considered experimental.
Magnacarto is much faster than Carto, but may not support the full range of features. However, the feature set is very close to the JavaScript reference implementation.
Due to the internal use of Go vs. JavaScript Magnacarto is much faster in parsing complex stylesheets. For openstreetmap-carto the difference is as large as 1.24s for Magnacarto vs. 10.08s for Carto on a machine with Intel Core i5-4300U, Linux x64 and 12 GB RAM (January 2016).
While in your Kosmtik root, run:
node index.js plugins --install kosmtik-magnacarto
Specify the alternate renderer with the --renderer command line option. E.g.:
node index.js serve --renderer magnacarto ...