scan.rs

// Licensed to the Apache Software Foundation (ASF) under one
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// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// 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
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

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

use datafusion::arrow::array::RecordBatch;
use datafusion::arrow::datatypes::SchemaRef as ArrowSchemaRef;
use datafusion::error::Result as DFResult;
use datafusion::execution::{SendableRecordBatchStream, TaskContext};
use datafusion::physical_expr::EquivalenceProperties;
use datafusion::physical_plan::stream::RecordBatchStreamAdapter;
use datafusion::physical_plan::{
    DisplayAs, ExecutionMode, ExecutionPlan, Partitioning, PlanProperties,
};
use futures::{Stream, TryStreamExt};
use iceberg::table::Table;

use crate::to_datafusion_error;

/// Manages the scanning process of an Iceberg [`Table`], encapsulating the
/// necessary details and computed properties required for execution planning.
#[derive(Debug)]
pub(crate) struct IcebergTableScan {
    /// A table in the catalog.
    table: Table,
    /// A reference-counted arrow `Schema`.
    schema: ArrowSchemaRef,
    /// Stores certain, often expensive to compute,
    /// plan properties used in query optimization.
    plan_properties: PlanProperties,
}

impl IcebergTableScan {
    /// Creates a new [`IcebergTableScan`] object.
    pub(crate) fn new(table: Table, schema: ArrowSchemaRef) -> Self {
        let plan_properties = Self::compute_properties(schema.clone());

        Self {
            table,
            schema,
            plan_properties,
        }
    }

    /// Computes [`PlanProperties`] used in query optimization.
    fn compute_properties(schema: ArrowSchemaRef) -> PlanProperties {
        // TODO:
        // This is more or less a placeholder, to be replaced
        // once we support output-partitioning
        PlanProperties::new(
            EquivalenceProperties::new(schema),
            Partitioning::UnknownPartitioning(1),
            ExecutionMode::Bounded,
        )
    }
}

impl ExecutionPlan for IcebergTableScan {
    fn name(&self) -> &str {
        "IcebergTableScan"
    }

    fn as_any(&self) -> &dyn Any {
        self
    }

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

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

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

    fn execute(
        &self,
        _partition: usize,
        _context: Arc<TaskContext>,
    ) -> DFResult<SendableRecordBatchStream> {
        let fut = get_batch_stream(self.table.clone());
        let stream = futures::stream::once(fut).try_flatten();

        Ok(Box::pin(RecordBatchStreamAdapter::new(
            self.schema.clone(),
            stream,
        )))
    }
}

impl DisplayAs for IcebergTableScan {
    fn fmt_as(
        &self,
        _t: datafusion::physical_plan::DisplayFormatType,
        f: &mut std::fmt::Formatter,
    ) -> std::fmt::Result {
        write!(f, "IcebergTableScan")
    }
}

/// Asynchronously retrieves a stream of [`RecordBatch`] instances
/// from a given table.
///
/// This function initializes a [`TableScan`], builds it,
/// and then converts it into a stream of Arrow [`RecordBatch`]es.
async fn get_batch_stream(
    table: Table,
) -> DFResult<Pin<Box<dyn Stream<Item = DFResult<RecordBatch>> + Send>>> {
    let table_scan = table.scan().build().map_err(to_datafusion_error)?;

    let stream = table_scan
        .to_arrow()
        .await
        .map_err(to_datafusion_error)?
        .map_err(to_datafusion_error);

    Ok(Box::pin(stream))
}