datafusion_physical_plan/

empty.rs

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//
//   http://www.apache.org/licenses/LICENSE-2.0
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//! EmptyRelation with produce_one_row=false execution plan

use std::any::Any;
use std::sync::Arc;

use super::{
    common, DisplayAs, ExecutionMode, PlanProperties, SendableRecordBatchStream,
    Statistics,
};
use crate::{memory::MemoryStream, DisplayFormatType, ExecutionPlan, Partitioning};

use arrow::datatypes::SchemaRef;
use arrow::record_batch::RecordBatch;
use datafusion_common::{internal_err, Result};
use datafusion_execution::TaskContext;
use datafusion_physical_expr::EquivalenceProperties;

use log::trace;

/// Execution plan for empty relation with produce_one_row=false
#[derive(Debug, Clone)]
pub struct EmptyExec {
    /// The schema for the produced row
    schema: SchemaRef,
    /// Number of partitions
    partitions: usize,
    cache: PlanProperties,
}

impl EmptyExec {
    /// Create a new EmptyExec
    pub fn new(schema: SchemaRef) -> Self {
        let cache = Self::compute_properties(Arc::clone(&schema), 1);
        EmptyExec {
            schema,
            partitions: 1,
            cache,
        }
    }

    /// Create a new EmptyExec with specified partition number
    pub fn with_partitions(mut self, partitions: usize) -> Self {
        self.partitions = partitions;
        // Changing partitions may invalidate output partitioning, so update it:
        let output_partitioning = Self::output_partitioning_helper(self.partitions);
        self.cache = self.cache.with_partitioning(output_partitioning);
        self
    }

    fn data(&self) -> Result<Vec<RecordBatch>> {
        Ok(vec![])
    }

    fn output_partitioning_helper(n_partitions: usize) -> Partitioning {
        Partitioning::UnknownPartitioning(n_partitions)
    }

    /// This function creates the cache object that stores the plan properties such as schema, equivalence properties, ordering, partitioning, etc.
    fn compute_properties(schema: SchemaRef, n_partitions: usize) -> PlanProperties {
        let eq_properties = EquivalenceProperties::new(schema);
        let output_partitioning = Self::output_partitioning_helper(n_partitions);
        PlanProperties::new(
            eq_properties,
            // Output Partitioning
            output_partitioning,
            // Execution Mode
            ExecutionMode::Bounded,
        )
    }
}

impl DisplayAs for EmptyExec {
    fn fmt_as(
        &self,
        t: DisplayFormatType,
        f: &mut std::fmt::Formatter,
    ) -> std::fmt::Result {
        match t {
            DisplayFormatType::Default | DisplayFormatType::Verbose => {
                write!(f, "EmptyExec")
            }
        }
    }
}

impl ExecutionPlan for EmptyExec {
    fn name(&self) -> &'static str {
        "EmptyExec"
    }

    /// Return a reference to Any that can be used for downcasting
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn properties(&self) -> &PlanProperties {
        &self.cache
    }

    fn children(&self) -> Vec<&Arc<dyn ExecutionPlan>> {
        vec![]
    }

    fn with_new_children(
        self: Arc<Self>,
        _: Vec<Arc<dyn ExecutionPlan>>,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        Ok(self)
    }

    fn execute(
        &self,
        partition: usize,
        context: Arc<TaskContext>,
    ) -> Result<SendableRecordBatchStream> {
        trace!("Start EmptyExec::execute for partition {} of context session_id {} and task_id {:?}", partition, context.session_id(), context.task_id());

        if partition >= self.partitions {
            return internal_err!(
                "EmptyExec invalid partition {} (expected less than {})",
                partition,
                self.partitions
            );
        }

        Ok(Box::pin(MemoryStream::try_new(
            self.data()?,
            Arc::clone(&self.schema),
            None,
        )?))
    }

    fn statistics(&self) -> Result<Statistics> {
        let batch = self
            .data()
            .expect("Create empty RecordBatch should not fail");
        Ok(common::compute_record_batch_statistics(
            &[batch],
            &self.schema,
            None,
        ))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test;
    use crate::with_new_children_if_necessary;

    #[tokio::test]
    async fn empty() -> Result<()> {
        let task_ctx = Arc::new(TaskContext::default());
        let schema = test::aggr_test_schema();

        let empty = EmptyExec::new(Arc::clone(&schema));
        assert_eq!(empty.schema(), schema);

        // We should have no results
        let iter = empty.execute(0, task_ctx)?;
        let batches = common::collect(iter).await?;
        assert!(batches.is_empty());

        Ok(())
    }

    #[test]
    fn with_new_children() -> Result<()> {
        let schema = test::aggr_test_schema();
        let empty = Arc::new(EmptyExec::new(Arc::clone(&schema)));

        let empty2 = with_new_children_if_necessary(
            Arc::clone(&empty) as Arc<dyn ExecutionPlan>,
            vec![],
        )?;
        assert_eq!(empty.schema(), empty2.schema());

        let too_many_kids = vec![empty2];
        assert!(
            with_new_children_if_necessary(empty, too_many_kids).is_err(),
            "expected error when providing list of kids"
        );
        Ok(())
    }

    #[tokio::test]
    async fn invalid_execute() -> Result<()> {
        let task_ctx = Arc::new(TaskContext::default());
        let schema = test::aggr_test_schema();
        let empty = EmptyExec::new(schema);

        // ask for the wrong partition
        assert!(empty.execute(1, Arc::clone(&task_ctx)).is_err());
        assert!(empty.execute(20, task_ctx).is_err());
        Ok(())
    }
}