private void hashInto(ByteBuffer key, byte[] buffer) throws DigestException {
        key.mark();
        digest.update(key);
        key.reset();
        digest.digest(buffer, 0, hashSize);
    }
The offset at which we have stored the given key
@param key The key to hash
@param buffer The buffer to store the hash into
storage/src/main/java/org/apache/kafka/storage/internals/log/SkimpyOffsetMap.java