I need to count daily orders per user. The data may arrive late for quite a long time. So i think i can use a MapState[String,Long] for key is date and value is the order num according to the date to store the count.But as time goes by, the key-value will be one more per key per day and the state size could be too big someday. Since the data won't be late for longer than a day ,i just need to store two days of data. In this situation, i need to remove the earliest date when the size of MapState[String,Int] reaches 3. But i find out that there isn't a size method for fink MapState.
I know i can use iterator to achieve this and this is exactly what i did. But since the java.util.Map has size method, why isn't there a size method for flink MapState?
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