The following two system properties are relevant for memory usage of the engine and should be further documented:

• "kie.repository.project.cache.size" (default 100)
• "kie.repository.project.versions.cache.size" (default 10)

[From Mario Fusco]

that number is not a size in memory but the number of releases (kjars stored in the in memory repo)
e.g. 10 = stores the last 10 releases in memory and throw away the 11th

[From Tibor Z.]

kie.repository.project.cache.size is the maximum number of KieModules that are cached
kie.repository.project.versions.cache.size means how many versions of a specific artifact are cached
so the first one is a global number of how many artifacts can be cached
the second one is how many versions of a specific artifact can be cached

it is about loading KieModules from cache
In short - this is used when getting a KieContainer based on a KieModule (KJar)
(you get a session then from a KieContainer)