presto-main/src/main/java/io/prestosql/sql/planner/planprinter/WindowOperatorStats.java/WindowOperatorStats/isMeaningful
class WindowOperatorStats:    private static boolean isMeaningful(DriverWindowInfo windowInfo)
    {
        // We are filtering out windowInfos without rows.
        //
        // The idea was to distinguish two types of problems:
        //
        // Data skew (should be visible in ExchangeOperator stats), e.g. when one partition is significantly larger than others.
        // In such case, WindowOperator will be inefficient because parallelism will go down.
        // Problems in WindowOperator execution itself.
        // If you included empty indexes in WO stats, the active WO stats would be overwhelmed by data skew problems.
        // Imagine situation when all data is in one partition (processed by 8 local WOs) but you have 1024 WOs total in plan
        // (128 nodes are idling till 1 node finishes processing WO).
        //
        // In such case you care how efficiently the only occupied 8 local operators were working (how many times index was rebuilt, how big it was etc,
        // did everyone get the same index or maybe there was some skew which could be prevent on the operator level etc.).
        // If you included all 127 remaining idling nodes in the average, the problems with running operators would be not visible
        // (in most cases you'd see the average values very low, no matter how well active operators are doing).
        //
        // So, in other words, it's to make stats more granular:
        // if you're looking for data distribution skew, keep an eye on ExchangeOperator stats.
        // If you're debugging execution of WO, focus on relevant stats for WOs.
        //
        // Keep in mind, though, that WO stats are very low level and tightly coupled to implementation.
        // They don't make sense to DBA, if he doesn't know execution engine and implementation of WOs.
        // It's mostly to help driving window function improvements by better understanding why some queries are slower than others.

        return windowInfo.getTotalRowsCount() > 0;
    }