public static int registerDeserializer(CacheableDeserializer<Cacheable> cd) {
    int idx = identifier.incrementAndGet();
    // No synchronization here because keys will be unique
    registeredDeserializers.put(idx, cd);
    return idx;
  }
Register the given {@link Cacheable} -- usually an hfileblock instance, these implement the
Cacheable Interface -- deserializer and generate a unique identifier id for it and return this
as our result.
@return the identifier of given cacheable deserializer
@see #getDeserializer(int)
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CacheableDeserializerIdManager.java