promql/extension_plan/

absent.rs

// Copyright 2023 Greptime Team
//
// Licensed 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::cmp::Ordering;
use std::collections::HashMap;
use std::pin::Pin;
use std::sync::Arc;
use std::task::{Context, Poll};

use datafusion::arrow::array::Array;
use datafusion::common::{DFSchemaRef, Result as DataFusionResult};
use datafusion::execution::context::TaskContext;
use datafusion::logical_expr::{Expr, LogicalPlan, UserDefinedLogicalNodeCore};
use datafusion::physical_expr::{
    EquivalenceProperties, LexRequirement, OrderingRequirements, PhysicalSortRequirement,
};
use datafusion::physical_plan::execution_plan::{Boundedness, EmissionType};
use datafusion::physical_plan::expressions::Column as ColumnExpr;
use datafusion::physical_plan::metrics::{BaselineMetrics, ExecutionPlanMetricsSet, MetricsSet};
use datafusion::physical_plan::{
    DisplayAs, DisplayFormatType, Distribution, ExecutionPlan, Partitioning, PlanProperties,
    RecordBatchStream, SendableRecordBatchStream,
};
use datafusion_common::DFSchema;
use datafusion_expr::{EmptyRelation, col};
use datatypes::arrow;
use datatypes::arrow::array::{ArrayRef, Float64Array, TimestampMillisecondArray};
use datatypes::arrow::datatypes::{DataType, Field, SchemaRef, TimeUnit};
use datatypes::arrow::record_batch::RecordBatch;
use datatypes::arrow_array::StringArray;
use datatypes::compute::SortOptions;
use futures::{Stream, StreamExt, ready};
use greptime_proto::substrait_extension as pb;
use prost::Message;
use snafu::ResultExt;

use crate::error::DeserializeSnafu;
use crate::extension_plan::{Millisecond, resolve_column_name, serialize_column_index};

#[derive(Debug, PartialEq, Eq, Hash)]
pub struct Absent {
    start: Millisecond,
    end: Millisecond,
    step: Millisecond,
    time_index_column: String,
    value_column: String,
    fake_labels: Vec<(String, String)>,
    input: LogicalPlan,
    output_schema: DFSchemaRef,
    unfix: Option<UnfixIndices>,
}

#[derive(Debug, PartialEq, Eq, Hash, PartialOrd)]
struct UnfixIndices {
    pub time_index_column_idx: u64,
    pub value_column_idx: u64,
}

impl PartialOrd for Absent {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        // compare on fields except schema and input
        (
            self.start,
            self.end,
            self.step,
            &self.time_index_column,
            &self.value_column,
            &self.fake_labels,
        )
            .partial_cmp(&(
                other.start,
                other.end,
                other.step,
                &other.time_index_column,
                &other.value_column,
                &other.fake_labels,
            ))
    }
}

impl UserDefinedLogicalNodeCore for Absent {
    fn name(&self) -> &str {
        Self::name()
    }

    fn inputs(&self) -> Vec<&LogicalPlan> {
        vec![&self.input]
    }

    fn schema(&self) -> &DFSchemaRef {
        &self.output_schema
    }

    fn expressions(&self) -> Vec<Expr> {
        if self.unfix.is_some() {
            return vec![];
        }

        vec![col(&self.time_index_column)]
    }

    fn necessary_children_exprs(&self, _output_columns: &[usize]) -> Option<Vec<Vec<usize>>> {
        if self.unfix.is_some() {
            return None;
        }

        let input_schema = self.input.schema();
        let time_index_idx = input_schema.index_of_column_by_name(None, &self.time_index_column)?;
        Some(vec![vec![time_index_idx]])
    }

    fn fmt_for_explain(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(
            f,
            "PromAbsent: start={}, end={}, step={}",
            self.start, self.end, self.step
        )
    }

    fn with_exprs_and_inputs(
        &self,
        _exprs: Vec<Expr>,
        inputs: Vec<LogicalPlan>,
    ) -> DataFusionResult<Self> {
        if inputs.is_empty() {
            return Err(datafusion::error::DataFusionError::Internal(
                "Absent must have at least one input".to_string(),
            ));
        }

        let input: LogicalPlan = inputs[0].clone();
        let input_schema = input.schema();

        if let Some(unfix) = &self.unfix {
            // transform indices to names
            let time_index_column = resolve_column_name(
                unfix.time_index_column_idx,
                input_schema,
                "Absent",
                "time index",
            )?;

            let value_column =
                resolve_column_name(unfix.value_column_idx, input_schema, "Absent", "value")?;

            // Recreate output schema with actual field names
            Self::try_new(
                self.start,
                self.end,
                self.step,
                time_index_column,
                value_column,
                self.fake_labels.clone(),
                input,
            )
        } else {
            Ok(Self {
                start: self.start,
                end: self.end,
                step: self.step,
                time_index_column: self.time_index_column.clone(),
                value_column: self.value_column.clone(),
                fake_labels: self.fake_labels.clone(),
                input,
                output_schema: self.output_schema.clone(),
                unfix: None,
            })
        }
    }
}

impl Absent {
    pub fn try_new(
        start: Millisecond,
        end: Millisecond,
        step: Millisecond,
        time_index_column: String,
        value_column: String,
        fake_labels: Vec<(String, String)>,
        input: LogicalPlan,
    ) -> DataFusionResult<Self> {
        let mut fields = vec![
            Field::new(
                &time_index_column,
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new(&value_column, DataType::Float64, true),
        ];

        // remove duplicate fake labels
        let mut fake_labels = fake_labels
            .into_iter()
            .collect::<HashMap<String, String>>()
            .into_iter()
            .collect::<Vec<_>>();
        fake_labels.sort_unstable_by(|a, b| a.0.cmp(&b.0));
        for (name, _) in fake_labels.iter() {
            fields.push(Field::new(name, DataType::Utf8, true));
        }

        let output_schema = Arc::new(DFSchema::from_unqualified_fields(
            fields.into(),
            HashMap::new(),
        )?);

        Ok(Self {
            start,
            end,
            step,
            time_index_column,
            value_column,
            fake_labels,
            input,
            output_schema,
            unfix: None,
        })
    }

    pub const fn name() -> &'static str {
        "prom_absent"
    }

    pub fn to_execution_plan(&self, exec_input: Arc<dyn ExecutionPlan>) -> Arc<dyn ExecutionPlan> {
        let output_schema = Arc::new(self.output_schema.as_arrow().clone());
        let properties = Arc::new(PlanProperties::new(
            EquivalenceProperties::new(output_schema.clone()),
            Partitioning::UnknownPartitioning(1),
            EmissionType::Incremental,
            Boundedness::Bounded,
        ));
        Arc::new(AbsentExec {
            start: self.start,
            end: self.end,
            step: self.step,
            time_index_column: self.time_index_column.clone(),
            value_column: self.value_column.clone(),
            fake_labels: self.fake_labels.clone(),
            output_schema: output_schema.clone(),
            input: exec_input,
            properties,
            metric: ExecutionPlanMetricsSet::new(),
        })
    }

    pub fn serialize(&self) -> Vec<u8> {
        let time_index_column_idx =
            serialize_column_index(self.input.schema(), &self.time_index_column);

        let value_column_idx = serialize_column_index(self.input.schema(), &self.value_column);

        pb::Absent {
            start: self.start,
            end: self.end,
            step: self.step,
            time_index_column_idx,
            value_column_idx,
            fake_labels: self
                .fake_labels
                .iter()
                .map(|(name, value)| pb::LabelPair {
                    key: name.clone(),
                    value: value.clone(),
                })
                .collect(),
            ..Default::default()
        }
        .encode_to_vec()
    }

    pub fn deserialize(bytes: &[u8]) -> DataFusionResult<Self> {
        let pb_absent = pb::Absent::decode(bytes).context(DeserializeSnafu)?;
        let placeholder_plan = LogicalPlan::EmptyRelation(EmptyRelation {
            produce_one_row: false,
            schema: Arc::new(DFSchema::empty()),
        });

        let unfix = UnfixIndices {
            time_index_column_idx: pb_absent.time_index_column_idx,
            value_column_idx: pb_absent.value_column_idx,
        };

        Ok(Self {
            start: pb_absent.start,
            end: pb_absent.end,
            step: pb_absent.step,
            time_index_column: String::new(),
            value_column: String::new(),
            fake_labels: pb_absent
                .fake_labels
                .iter()
                .map(|label| (label.key.clone(), label.value.clone()))
                .collect(),
            input: placeholder_plan,
            output_schema: Arc::new(DFSchema::empty()),
            unfix: Some(unfix),
        })
    }
}

#[derive(Debug)]
pub struct AbsentExec {
    start: Millisecond,
    end: Millisecond,
    step: Millisecond,
    time_index_column: String,
    value_column: String,
    fake_labels: Vec<(String, String)>,
    output_schema: SchemaRef,
    input: Arc<dyn ExecutionPlan>,
    properties: Arc<PlanProperties>,
    metric: ExecutionPlanMetricsSet,
}

impl ExecutionPlan for AbsentExec {
    fn as_any(&self) -> &dyn Any {
        self
    }

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

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

    fn required_input_distribution(&self) -> Vec<Distribution> {
        vec![Distribution::SinglePartition]
    }

    fn required_input_ordering(&self) -> Vec<Option<OrderingRequirements>> {
        let requirement = LexRequirement::from([PhysicalSortRequirement {
            expr: Arc::new(
                ColumnExpr::new_with_schema(&self.time_index_column, &self.input.schema()).unwrap(),
            ),
            options: Some(SortOptions {
                descending: false,
                nulls_first: false,
            }),
        }]);
        vec![Some(OrderingRequirements::new(requirement))]
    }

    fn maintains_input_order(&self) -> Vec<bool> {
        vec![false]
    }

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

    fn with_new_children(
        self: Arc<Self>,
        children: Vec<Arc<dyn ExecutionPlan>>,
    ) -> DataFusionResult<Arc<dyn ExecutionPlan>> {
        assert!(!children.is_empty());
        Ok(Arc::new(Self {
            start: self.start,
            end: self.end,
            step: self.step,
            time_index_column: self.time_index_column.clone(),
            value_column: self.value_column.clone(),
            fake_labels: self.fake_labels.clone(),
            output_schema: self.output_schema.clone(),
            input: children[0].clone(),
            properties: self.properties.clone(),
            metric: self.metric.clone(),
        }))
    }

    fn execute(
        &self,
        partition: usize,
        context: Arc<TaskContext>,
    ) -> DataFusionResult<SendableRecordBatchStream> {
        let baseline_metric = BaselineMetrics::new(&self.metric, partition);
        let batch_size = context.session_config().batch_size();
        let input = self.input.execute(partition, context)?;

        Ok(Box::pin(AbsentStream {
            end: self.end,
            step: self.step,
            batch_size,
            time_index_column_index: self
                .input
                .schema()
                .column_with_name(&self.time_index_column)
                .unwrap() // Safety: we have checked the column name in `try_new`
                .0,
            output_schema: self.output_schema.clone(),
            fake_labels: self.fake_labels.clone(),
            input,
            metric: baseline_metric,
            // Buffer for streaming output timestamps
            output_timestamps: Vec::new(),
            input_timestamps: Vec::new(),
            input_timestamp_offset: 0,
            // Current timestamp in the output range
            output_ts_cursor: self.start,
            input_finished: false,
        }))
    }

    fn metrics(&self) -> Option<MetricsSet> {
        Some(self.metric.clone_inner())
    }

    fn name(&self) -> &str {
        "AbsentExec"
    }
}

impl DisplayAs for AbsentExec {
    fn fmt_as(&self, t: DisplayFormatType, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match t {
            DisplayFormatType::Default
            | DisplayFormatType::Verbose
            | DisplayFormatType::TreeRender => {
                write!(
                    f,
                    "PromAbsentExec: start={}, end={}, step={}",
                    self.start, self.end, self.step
                )
            }
        }
    }
}

pub struct AbsentStream {
    end: Millisecond,
    step: Millisecond,
    batch_size: usize,
    time_index_column_index: usize,
    output_schema: SchemaRef,
    fake_labels: Vec<(String, String)>,
    input: SendableRecordBatchStream,
    metric: BaselineMetrics,
    // Buffer for streaming output timestamps
    output_timestamps: Vec<Millisecond>,
    // Current input timestamps being processed incrementally.
    input_timestamps: Vec<Millisecond>,
    input_timestamp_offset: usize,
    // Current timestamp in the output range
    output_ts_cursor: Millisecond,
    input_finished: bool,
}

impl RecordBatchStream for AbsentStream {
    fn schema(&self) -> SchemaRef {
        self.output_schema.clone()
    }
}

impl Stream for AbsentStream {
    type Item = DataFusionResult<RecordBatch>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        loop {
            if self.has_pending_input_timestamps() {
                let timer = std::time::Instant::now();
                if let Err(e) = self.process_input_batch() {
                    return Poll::Ready(Some(Err(e)));
                }
                self.metric.elapsed_compute().add_elapsed(timer);

                match self.flush_output_batch() {
                    Ok(Some(batch)) => return Poll::Ready(Some(Ok(batch))),
                    Ok(None) => continue,
                    Err(e) => return Poll::Ready(Some(Err(e))),
                }
            }

            if self.input_finished {
                let timer = std::time::Instant::now();
                if let Err(e) = self.process_remaining_absent_timestamps() {
                    return Poll::Ready(Some(Err(e)));
                }
                self.metric.elapsed_compute().add_elapsed(timer);

                match self.flush_output_batch() {
                    Ok(Some(batch)) => return Poll::Ready(Some(Ok(batch))),
                    Ok(None) => return Poll::Ready(None),
                    Err(e) => return Poll::Ready(Some(Err(e))),
                }
            }

            match ready!(self.input.poll_next_unpin(cx)) {
                Some(Ok(batch)) => {
                    let timer = std::time::Instant::now();
                    if let Err(e) = self.buffer_input_timestamps(&batch) {
                        return Poll::Ready(Some(Err(e)));
                    }
                    self.metric.elapsed_compute().add_elapsed(timer);
                }
                Some(Err(e)) => return Poll::Ready(Some(Err(e))),
                None => {
                    self.input_finished = true;
                }
            }
        }
    }
}

impl AbsentStream {
    fn buffer_input_timestamps(&mut self, batch: &RecordBatch) -> DataFusionResult<()> {
        let timestamp_array = batch.column(self.time_index_column_index);
        let milli_ts_array = arrow::compute::cast(
            timestamp_array,
            &DataType::Timestamp(TimeUnit::Millisecond, None),
        )?;
        let timestamp_array = milli_ts_array
            .as_any()
            .downcast_ref::<TimestampMillisecondArray>()
            .unwrap();
        self.input_timestamps.clear();
        self.input_timestamps
            .extend_from_slice(timestamp_array.values());
        self.input_timestamp_offset = 0;
        Ok(())
    }

    fn has_pending_input_timestamps(&self) -> bool {
        self.input_timestamp_offset < self.input_timestamps.len()
    }

    fn process_input_batch(&mut self) -> DataFusionResult<()> {
        while self.input_timestamp_offset < self.input_timestamps.len() {
            let input_ts = self.input_timestamps[self.input_timestamp_offset];

            // Generate absent timestamps up to this input timestamp
            while self.output_ts_cursor < input_ts && self.output_ts_cursor <= self.end {
                self.output_timestamps.push(self.output_ts_cursor);
                self.output_ts_cursor += self.step;

                if self.output_timestamps.len() >= self.batch_size {
                    return Ok(());
                }
            }

            // Skip the input timestamp if it matches our cursor
            if self.output_ts_cursor == input_ts {
                self.output_ts_cursor += self.step;
            }

            self.input_timestamp_offset += 1;
        }

        self.input_timestamps.clear();
        self.input_timestamp_offset = 0;
        Ok(())
    }

    fn process_remaining_absent_timestamps(&mut self) -> DataFusionResult<()> {
        while self.output_ts_cursor <= self.end {
            self.output_timestamps.push(self.output_ts_cursor);
            self.output_ts_cursor += self.step;

            if self.output_timestamps.len() >= self.batch_size {
                return Ok(());
            }
        }
        Ok(())
    }

    fn flush_output_batch(&mut self) -> DataFusionResult<Option<RecordBatch>> {
        if self.output_timestamps.is_empty() {
            return Ok(None);
        }

        let timestamps = if self.output_timestamps.len() <= self.batch_size {
            std::mem::take(&mut self.output_timestamps)
        } else {
            let remaining = self.output_timestamps.split_off(self.batch_size);
            std::mem::replace(&mut self.output_timestamps, remaining)
        };

        let mut columns: Vec<ArrayRef> = Vec::with_capacity(self.output_schema.fields().len());
        let num_rows = timestamps.len();
        columns.push(Arc::new(TimestampMillisecondArray::from(timestamps)) as _);
        columns.push(Arc::new(Float64Array::from(vec![1.0; num_rows])) as _);

        for (_, value) in self.fake_labels.iter() {
            columns.push(Arc::new(StringArray::from_iter(std::iter::repeat_n(
                Some(value.clone()),
                num_rows,
            ))) as _);
        }

        let batch = RecordBatch::try_new(self.output_schema.clone(), columns)?;

        Ok(Some(batch))
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use datafusion::arrow::datatypes::{DataType, Field, Schema, TimeUnit};
    use datafusion::arrow::record_batch::RecordBatch;
    use datafusion::catalog::memory::DataSourceExec;
    use datafusion::datasource::memory::MemorySourceConfig;
    use datafusion::prelude::{SessionConfig, SessionContext};
    use datatypes::arrow::array::{Float64Array, TimestampMillisecondArray};

    use super::*;

    #[tokio::test]
    async fn test_absent_basic() {
        let schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        // Input has timestamps: 0, 2000, 4000
        let timestamp_array = Arc::new(TimestampMillisecondArray::from(vec![0, 2000, 4000]));
        let value_array = Arc::new(Float64Array::from(vec![1.0, 2.0, 3.0]));
        let batch =
            RecordBatch::try_new(schema.clone(), vec![timestamp_array, value_array]).unwrap();

        let memory_exec = DataSourceExec::new(Arc::new(
            MemorySourceConfig::try_new(&[vec![batch]], schema, None).unwrap(),
        ));

        let output_schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        let absent_exec = AbsentExec {
            start: 0,
            end: 5000,
            step: 1000,
            time_index_column: "timestamp".to_string(),
            value_column: "value".to_string(),
            fake_labels: vec![],
            output_schema: output_schema.clone(),
            input: Arc::new(memory_exec),
            properties: Arc::new(PlanProperties::new(
                EquivalenceProperties::new(output_schema.clone()),
                Partitioning::UnknownPartitioning(1),
                EmissionType::Incremental,
                Boundedness::Bounded,
            )),
            metric: ExecutionPlanMetricsSet::new(),
        };

        let session_ctx = SessionContext::new();
        let task_ctx = session_ctx.task_ctx();
        let mut stream = absent_exec.execute(0, task_ctx).unwrap();

        // Collect all output batches
        let mut output_timestamps = Vec::new();
        while let Some(batch_result) = stream.next().await {
            let batch = batch_result.unwrap();
            let ts_array = batch
                .column(0)
                .as_any()
                .downcast_ref::<TimestampMillisecondArray>()
                .unwrap();
            for i in 0..ts_array.len() {
                if !ts_array.is_null(i) {
                    let ts = ts_array.value(i);
                    output_timestamps.push(ts);
                }
            }
        }

        // Should output absent timestamps: 1000, 3000, 5000
        // (0, 2000, 4000 exist in input, so 1000, 3000, 5000 are absent)
        assert_eq!(output_timestamps, vec![1000, 3000, 5000]);
    }

    #[tokio::test]
    async fn test_absent_empty_input() {
        let schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        // Empty input
        let memory_exec = DataSourceExec::new(Arc::new(
            MemorySourceConfig::try_new(&[vec![]], schema, None).unwrap(),
        ));

        let output_schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));
        let absent_exec = AbsentExec {
            start: 0,
            end: 2000,
            step: 1000,
            time_index_column: "timestamp".to_string(),
            value_column: "value".to_string(),
            fake_labels: vec![],
            output_schema: output_schema.clone(),
            input: Arc::new(memory_exec),
            properties: Arc::new(PlanProperties::new(
                EquivalenceProperties::new(output_schema.clone()),
                Partitioning::UnknownPartitioning(1),
                EmissionType::Incremental,
                Boundedness::Bounded,
            )),
            metric: ExecutionPlanMetricsSet::new(),
        };

        let session_ctx = SessionContext::new();
        let task_ctx = session_ctx.task_ctx();
        let mut stream = absent_exec.execute(0, task_ctx).unwrap();

        // Collect all output timestamps
        let mut output_timestamps = Vec::new();
        while let Some(batch_result) = stream.next().await {
            let batch = batch_result.unwrap();
            let ts_array = batch
                .column(0)
                .as_any()
                .downcast_ref::<TimestampMillisecondArray>()
                .unwrap();
            for i in 0..ts_array.len() {
                if !ts_array.is_null(i) {
                    let ts = ts_array.value(i);
                    output_timestamps.push(ts);
                }
            }
        }

        // Should output all timestamps in range: 0, 1000, 2000
        assert_eq!(output_timestamps, vec![0, 1000, 2000]);
    }

    #[tokio::test]
    async fn test_absent_respects_session_batch_size_for_large_gap() {
        let schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        let timestamp_array = Arc::new(TimestampMillisecondArray::from(vec![9]));
        let value_array = Arc::new(Float64Array::from(vec![1.0]));
        let batch =
            RecordBatch::try_new(schema.clone(), vec![timestamp_array, value_array]).unwrap();

        let memory_exec = DataSourceExec::new(Arc::new(
            MemorySourceConfig::try_new(&[vec![batch]], schema, None).unwrap(),
        ));

        let output_schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        let absent_exec = AbsentExec {
            start: 0,
            end: 10,
            step: 1,
            time_index_column: "timestamp".to_string(),
            value_column: "value".to_string(),
            fake_labels: vec![],
            output_schema: output_schema.clone(),
            input: Arc::new(memory_exec),
            properties: Arc::new(PlanProperties::new(
                EquivalenceProperties::new(output_schema.clone()),
                Partitioning::UnknownPartitioning(1),
                EmissionType::Incremental,
                Boundedness::Bounded,
            )),
            metric: ExecutionPlanMetricsSet::new(),
        };

        let session_ctx = SessionContext::new_with_config(SessionConfig::new().with_batch_size(3));
        let task_ctx = session_ctx.task_ctx();
        let mut stream = absent_exec.execute(0, task_ctx).unwrap();

        let mut batch_sizes = Vec::new();
        let mut output_timestamps = Vec::new();
        while let Some(batch_result) = stream.next().await {
            let batch = batch_result.unwrap();
            batch_sizes.push(batch.num_rows());

            let ts_array = batch
                .column(0)
                .as_any()
                .downcast_ref::<TimestampMillisecondArray>()
                .unwrap();
            for i in 0..ts_array.len() {
                if !ts_array.is_null(i) {
                    output_timestamps.push(ts_array.value(i));
                }
            }
        }

        assert_eq!(batch_sizes, vec![3, 3, 3, 1]);
        assert_eq!(output_timestamps, vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 10]);
    }

    #[tokio::test]
    async fn test_absent_resumes_same_input_timestamp_after_batch_flush() {
        let schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        let timestamp_array = Arc::new(TimestampMillisecondArray::from(vec![9]));
        let value_array = Arc::new(Float64Array::from(vec![1.0]));
        let batch =
            RecordBatch::try_new(schema.clone(), vec![timestamp_array, value_array]).unwrap();

        let memory_exec = DataSourceExec::new(Arc::new(
            MemorySourceConfig::try_new(&[vec![batch]], schema, None).unwrap(),
        ));

        let output_schema = Arc::new(Schema::new(vec![
            Field::new(
                "timestamp",
                DataType::Timestamp(TimeUnit::Millisecond, None),
                true,
            ),
            Field::new("value", DataType::Float64, true),
        ]));

        let absent_exec = AbsentExec {
            start: 0,
            end: 9,
            step: 1,
            time_index_column: "timestamp".to_string(),
            value_column: "value".to_string(),
            fake_labels: vec![],
            output_schema: output_schema.clone(),
            input: Arc::new(memory_exec),
            properties: Arc::new(PlanProperties::new(
                EquivalenceProperties::new(output_schema.clone()),
                Partitioning::UnknownPartitioning(1),
                EmissionType::Incremental,
                Boundedness::Bounded,
            )),
            metric: ExecutionPlanMetricsSet::new(),
        };

        let session_ctx = SessionContext::new_with_config(SessionConfig::new().with_batch_size(3));
        let task_ctx = session_ctx.task_ctx();
        let mut stream = absent_exec.execute(0, task_ctx).unwrap();

        let mut output_timestamps = Vec::new();
        while let Some(batch_result) = stream.next().await {
            let batch = batch_result.unwrap();
            let ts_array = batch
                .column(0)
                .as_any()
                .downcast_ref::<TimestampMillisecondArray>()
                .unwrap();
            for i in 0..ts_array.len() {
                if !ts_array.is_null(i) {
                    output_timestamps.push(ts_array.value(i));
                }
            }
        }

        assert_eq!(output_timestamps, vec![0, 1, 2, 3, 4, 5, 6, 7, 8]);
    }
}