The purpose of this article is to explain the limits in String length when using PDX serialization - this article applies to GemFire versions 7 and later.
But note that PDX serialization poses another limit that can in theory have impact. Each object that is serialized with PDX has a 2GB limit to its total serialized size that includes nested objects. This is because the PDX header records the serialized length of the object bytes as a signed 32bit int
GemFire 7 and later