A Scala TrieMap is a trie-based concurrent scalable map implementation. Unlike normal trie maps, a Scala TrieMap has an efficient, non-blocking, O(1) time snapshot operation (and a slightly optimized readOnlySnapshot) operation.
Absolute performance of a TrieMap is slightly below the JDK8 ConcurrentHashMap, but the advantage is that it provides consistent iterators, something that concurrent data structures typically do not have. This means that you can capture all the elements in the trie at one point in time (performance numbers and analysis here). You should use the TrieMap if you need to capture all the elements at once (e.g. to list all its elements in the UI, or to consistently analyze them).