Using gzip, cache could be stored more efficiently space wise. For reference, my PHPStan cache folder is 16MB, my Psalm folder is 385MB on a project, they run in about the same time.

Symfony uses gzinflate / gzdeflate to decorate the cache marshaler, Psalm could do the same. It provides quite an improvement over nothing or igbinary, gzip features are also bundles in PHP while igbinary might require additional extensions.

cc @bendavies @orklah