public boolean entryRequiresOldValue(Object key) {
    if (hasCQs()) {
      if (!CqServiceProvider.MAINTAIN_KEYS) {
        return true;
      }
      for (final ServerCQ cq : cqs.values()) {
        if (cq.isOldValueRequiredForQueryProcessing(key)) {
          return true;
        }
      }
    }
    return false;
  }
Returns if old value is required for CQ processing or not. In order to reduce the query
processing time CQ caches the event keys its already seen, if the key is cached than the old
value is not required.
geode-core/src/main/java/org/apache/geode/internal/cache/FilterProfile.java