rust/datafusion/src/physical_plan/explain.rs

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// distributed with this work for additional information
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// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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//! Defines the EXPLAIN operator

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

use crate::error::{DataFusionError, Result};
use crate::{
    logical_plan::StringifiedPlan,
    physical_plan::{common::SizedRecordBatchStream, ExecutionPlan},
};
use arrow::{array::StringBuilder, datatypes::SchemaRef, record_batch::RecordBatch};

use crate::physical_plan::Partitioning;

use super::SendableRecordBatchStream;
use async_trait::async_trait;

/// Explain execution plan operator. This operator contains the string
/// values of the various plans it has when it is created, and passes
/// them to its output.
#[derive(Debug, Clone)]
pub struct ExplainExec {
    /// The schema that this exec plan node outputs
    schema: SchemaRef,
    /// The strings to be printed
    stringified_plans: Vec<StringifiedPlan>,
}

impl ExplainExec {
    /// Create a new ExplainExec
    pub fn new(schema: SchemaRef, stringified_plans: Vec<StringifiedPlan>) -> Self {
        ExplainExec {
            schema,
            stringified_plans,
        }
    }

    /// The strings to be printed
    pub fn stringified_plans(&self) -> &[StringifiedPlan] {
        &self.stringified_plans
    }
}

#[async_trait]
impl ExecutionPlan for ExplainExec {
    /// Return a reference to Any that can be used for downcasting
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn schema(&self) -> SchemaRef {
        self.schema.clone()
    }

    fn children(&self) -> Vec<Arc<dyn ExecutionPlan>> {
        // this is a leaf node and has no children
        vec![]
    }

    /// Get the output partitioning of this plan
    fn output_partitioning(&self) -> Partitioning {
        Partitioning::UnknownPartitioning(1)
    }

    fn with_new_children(
        &self,
        children: Vec<Arc<dyn ExecutionPlan>>,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        if children.is_empty() {
            Ok(Arc::new(self.clone()))
        } else {
            Err(DataFusionError::Internal(format!(
                "Children cannot be replaced in {:?}",
                self
            )))
        }
    }

    async fn execute(&self, partition: usize) -> Result<SendableRecordBatchStream> {
        if 0 != partition {
            return Err(DataFusionError::Internal(format!(
                "ExplainExec invalid partition {}",
                partition
            )));
        }

        let mut type_builder = StringBuilder::new(self.stringified_plans.len());
        let mut plan_builder = StringBuilder::new(self.stringified_plans.len());

        for p in &self.stringified_plans {
            type_builder.append_value(&String::from(&p.plan_type))?;
            plan_builder.append_value(&*p.plan)?;
        }

        let record_batch = RecordBatch::try_new(
            self.schema.clone(),
            vec![
                Arc::new(type_builder.finish()),
                Arc::new(plan_builder.finish()),
            ],
        )?;

        Ok(Box::pin(SizedRecordBatchStream::new(
            self.schema.clone(),
            vec![Arc::new(record_batch)],
        )))
    }
}