Does that answer your question? Because I’m not sure what you mean by the key being attached to the Tx.

The difference is say you have a tx1 on thread 1 then on the same
thread you ask for the group, if it is in the transaction controls
whether or not that pending update is seen.

Example:

  tx1 starts
  // Note key1 is in group 1
  cache.put(key1, someValue);

  Set<K> keys = cache.getGroup("group1");
  // The keys would contain key1 if taking part of transaction.