Cache Invalidation Concept in Hybris
The core of a Hybris Cluster is a network communication system that makes sure the cache of each individual cluster member only holds valid data. The nodes in the Hybris Cluster communicate using TCP (JGroups) or UDP, by sending signals to other nodes that mark some cache entries as invalid because a database item has been changed. The following is the overview of the cache invalidation process:
(1) A description of a product has changed. Therefore, all cache entries referring to the product are invalid.
(2) A cluster node where the modification has been done sends a notification to all cluster nodes that all cache entries holding the product are invalid.
(3) Nodes that hold the product in their cache discard the cached data of the product and re-retrieve the product from the database the next time the product is used.
node之間用于通知cache invalidation的協定有UDP Multicast, UDP Unicast, or JGroups.各有優缺點：
(1) JGroups provides the fastest communication and can be used both in the cloud for testing purposes and in a LAN or WAN network.
(2) UDP Multicast has some limitations in that some routers do not allow multicast network traffic by default. Amazon Elastic Compute Cloud (Amazon EC2) does not work using UDP, either.
Cache Invalidation Concept in Netweaver
SAP help上分了13個步驟詳細講解：