Looking at the go version[1] I am not sure if will work as expected. Maps in go are not thread safe.[2] So it could be the go version is out performing the others do to the lack of synchronisation. There are several ways to fix this in go, the easiest might just be to use a mutex around the accesses to the cache. But it would probably be better to use a readers writers lock.
edit: (that said I am not sure if the C version is thread safe either I haven't read the docs for the hash table he is using.)
edit 2: (looks like the C version is not thread safe either).
[1] https://github.com/grahamking/Key-Value-Polyglot/blob/master...