Disk based cache.
It's good that there is an in memory cache to not have to download the same artefacts unnecessarily, but it doesn't need to be in memory, it could be on disk. That would also allow it to be much larger.
➤ David Brandt commented:
FYI online discussion regarding disk caching and cleanup in Asana/bazels3cache or similar proxies vs in bazel itself: https://github.com/bazelbuild/bazel/issues/5139 . The TL;DR is that there are mixed opinions regarding delegating the responsibility to an external cache, but nobody has yet taken the time to implement the cleanup capability in bazel. The theory being that Googlers, being the primary contributors, mostly use remote execution, thus don't really care that much.