mp. In the described implementation, we
demonstrated one way of approaching this question by storing sets of
transactions per timestamp in <code>MapState&lt;Long, Set&lt;Transaction&gt;&gt;</code>. Such
a choice, however, might have a more significant effect on performance
than might be anticipated. The reason is that Flink does not currently
provide a native <code>Set</code> serializer and will enforce a fallback to the less
efficient <a href="//nightlies.apache.org/flink/flink-docs-release-1.11/dev/types_