presto-main/src/main/java/io/prestosql/operator/TopNRowNumberOperator.java/TopNRowNumberOperator/updateMemoryReservation
class TopNRowNumberOperator:    private boolean updateMemoryReservation()
    {
        // TODO: may need to use trySetMemoryReservation with a compaction to free memory (but that may cause GC pressure)
        localUserMemoryContext.setBytes(groupedTopNBuilder.getEstimatedSizeInBytes());
        return operatorContext.isWaitingForMemory().isDone();
    }