It is critical to be aware of the impact of HTTP session size on performance. Performance has an inverse relationship with the size of the session data that needs to be persisted. Session data is stored in HADB in a serialized manner. There is an overhead in serializing the data and inserting it as a BLOB and also deserializing it for retrieval.
Tests have shown that for a session size up to 24KB, performance remains unchanged. When the session size exceeds 100KB, and the same back-end store is used for the same number of connections, throughput drops by 90%.
It is important to pay attention while determining the HTTP session size. If you are creating large HTTP session objects, calculate the HADB nodes as discussed in Tuning HADB.