vector-clock

We have a large high-performance software system which consists of multiple interacting Java processes (not EJBs). Each process can be on the same machine or on a different machine. Certain events are generated in one process, and are then propagated in different ways to other processes for further processing and so on. For benchmarking purposes, we need to create a log of when each event passed through a "checkpoint", eventually combine these logs to obtain a timeline of how each event propagated through the system and with what latency (of course, process switching and IPC adds latency,

I understand the need for vector clocks in terms of scalar logical clocks failing to provide enough information to tell whether there is an update conflict in a key value store update for example. But I am not sure what problem is still unsolved by vector clocks and then solved by the more bulky matrix clocks? In an eventual consistency environment all messages ever created by a system need to be kept until every peer has received the message (== eventual consistency). But you don't want to keep messages for ever, so you need to have a way to tell which messages were received by all nodes and