public int getOldValSize() {
    int oldSize = 0;
    if (hasOldValue()) {
      try {
        oldSize = CachedDeserializableFactory.calcMemSize(basicGetOldValue());
      } catch (IllegalArgumentException iae) {
        logger.warn("DataStore failed to calculate size of old value",
            iae);
        oldSize = 0;
      }
    }
    return oldSize;
  }
Compute an estimate of the size of the old value

@return the size of serialized bytes for the old value
geode-core/src/main/java/org/apache/geode/internal/cache/EntryEventImpl.java