During initialization, we currently lookup a handle to get the initialCoder:

try {
    MethodHandle initCoder = JLA.stringConcatHelper("initialCoder", methodType(long.class));
    INITIAL_CODER = (long) initCoder.invoke();
} catch (Throwable e) {
    throw new AssertionError(e);
}

Supplying a shared secret method in JLA instead reduces initialization overhead by a few million instructions (~0.5ms).