presto-main/src/main/java/io/prestosql/execution/SqlTaskExecution.java/SqlTaskExecution/createDriverRunner
class SqlTaskExecution:        public DriverSplitRunner createDriverRunner(@Nullable ScheduledSplit partitionedSplit, Lifespan lifespan)
        {
            checkLifespan(driverFactory.getPipelineExecutionStrategy(), lifespan);
            status.incrementPendingCreation(pipelineContext.getPipelineId(), lifespan);
            // create driver context immediately so the driver existence is recorded in the stats
            // the number of drivers is used to balance work across nodes
            DriverContext driverContext = pipelineContext.addDriverContext(lifespan);
            return new DriverSplitRunner(this, driverContext, partitionedSplit, lifespan);
        }