row_hash.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// 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.

//! Hash aggregation

use std::sync::Arc;
use std::task::{Context, Poll};
use std::vec;

use crate::aggregates::group_values::{new_group_values, GroupValues};
use crate::aggregates::order::GroupOrderingFull;
use crate::aggregates::{
    evaluate_group_by, evaluate_many, evaluate_optional, group_schema, AggregateMode,
    PhysicalGroupBy,
};
use crate::common::IPCWriter;
use crate::metrics::{BaselineMetrics, RecordOutput};
use crate::sorts::sort::{read_spill_as_stream, sort_batch};
use crate::sorts::streaming_merge;
use crate::stream::RecordBatchStreamAdapter;
use crate::{aggregates, ExecutionPlan, PhysicalExpr};
use crate::{RecordBatchStream, SendableRecordBatchStream};

use arrow::array::*;
use arrow::{datatypes::SchemaRef, record_batch::RecordBatch};
use arrow_schema::SortOptions;
use datafusion_common::{DataFusionError, Result};
use datafusion_execution::disk_manager::RefCountedTempFile;
use datafusion_execution::memory_pool::proxy::VecAllocExt;
use datafusion_execution::memory_pool::{MemoryConsumer, MemoryReservation};
use datafusion_execution::runtime_env::RuntimeEnv;
use datafusion_execution::TaskContext;
use datafusion_expr::{EmitTo, GroupsAccumulator};
use datafusion_physical_expr::expressions::Column;
use datafusion_physical_expr::{
    AggregateExpr, GroupsAccumulatorAdapter, PhysicalSortExpr,
};

use futures::ready;
use futures::stream::{Stream, StreamExt};
use log::debug;

#[derive(Debug, Clone)]
/// This object tracks the aggregation phase (input/output)
pub(crate) enum ExecutionState {
    ReadingInput,
    /// When producing output, the remaining rows to output are stored
    /// here and are sliced off as needed in batch_size chunks
    ProducingOutput(RecordBatch),
    Done,
}

use super::order::GroupOrdering;
use super::AggregateExec;

/// This encapsulates the spilling state
struct SpillState {
    /// If data has previously been spilled, the locations of the
    /// spill files (in Arrow IPC format)
    spills: Vec<RefCountedTempFile>,

    /// Sorting expression for spilling batches
    spill_expr: Vec<PhysicalSortExpr>,

    /// Schema for spilling batches
    spill_schema: SchemaRef,

    /// true when streaming merge is in progress
    is_stream_merging: bool,

    /// aggregate_arguments for merging spilled data
    merging_aggregate_arguments: Vec<Vec<Arc<dyn PhysicalExpr>>>,

    /// GROUP BY expressions for merging spilled data
    merging_group_by: PhysicalGroupBy,
}

/// HashTable based Grouping Aggregator
///
/// # Design Goals
///
/// This structure is designed so that updating the aggregates can be
/// vectorized (done in a tight loop) without allocations. The
/// accumulator state is *not* managed by this operator (e.g in the
/// hash table) and instead is delegated to the individual
/// accumulators which have type specialized inner loops that perform
/// the aggregation.
///
/// # Architecture
///
/// ```text
///
///     Assigns a consecutive group           internally stores aggregate values
///     index for each unique set                     for all groups
///         of group values
///
///         ┌────────────┐              ┌──────────────┐       ┌──────────────┐
///         │ ┌────────┐ │              │┌────────────┐│       │┌────────────┐│
///         │ │  "A"   │ │              ││accumulator ││       ││accumulator ││
///         │ ├────────┤ │              ││     0      ││       ││     N      ││
///         │ │  "Z"   │ │              ││ ┌────────┐ ││       ││ ┌────────┐ ││
///         │ └────────┘ │              ││ │ state  │ ││       ││ │ state  │ ││
///         │            │              ││ │┌─────┐ │ ││  ...  ││ │┌─────┐ │ ││
///         │    ...     │              ││ │├─────┤ │ ││       ││ │├─────┤ │ ││
///         │            │              ││ │└─────┘ │ ││       ││ │└─────┘ │ ││
///         │            │              ││ │        │ ││       ││ │        │ ││
///         │ ┌────────┐ │              ││ │  ...   │ ││       ││ │  ...   │ ││
///         │ │  "Q"   │ │              ││ │        │ ││       ││ │        │ ││
///         │ └────────┘ │              ││ │┌─────┐ │ ││       ││ │┌─────┐ │ ││
///         │            │              ││ │└─────┘ │ ││       ││ │└─────┘ │ ││
///         └────────────┘              ││ └────────┘ ││       ││ └────────┘ ││
///                                     │└────────────┘│       │└────────────┘│
///                                     └──────────────┘       └──────────────┘
///
///         group_values                             accumulators
///
///  ```
///
/// For example, given a query like `COUNT(x), SUM(y) ... GROUP BY z`,
/// [`group_values`] will store the distinct values of `z`. There will
/// be one accumulator for `COUNT(x)`, specialized for the data type
/// of `x` and one accumulator for `SUM(y)`, specialized for the data
/// type of `y`.
///
/// # Description
///
/// [`group_values`] does not store any aggregate state inline. It only
/// assigns "group indices", one for each (distinct) group value. The
/// accumulators manage the in-progress aggregate state for each
/// group, with the group values themselves are stored in
/// [`group_values`] at the corresponding group index.
///
/// The accumulator state (e.g partial sums) is managed by and stored
/// by a [`GroupsAccumulator`] accumulator. There is one accumulator
/// per aggregate expression (COUNT, AVG, etc) in the
/// stream. Internally, each `GroupsAccumulator` manages the state for
/// multiple groups, and is passed `group_indexes` during update. Note
/// The accumulator state is not managed by this operator (e.g in the
/// hash table).
///
/// [`group_values`]: Self::group_values
///
/// # Spilling
///
/// The sizes of group values and accumulators can become large. Before that causes out of memory,
/// this hash aggregator outputs partial states early for partial aggregation or spills to local
/// disk using Arrow IPC format for final aggregation. For every input [`RecordBatch`], the memory
/// manager checks whether the new input size meets the memory configuration. If not, outputting or
/// spilling happens. For outputting, the final aggregation takes care of re-grouping. For spilling,
/// later stream-merge sort on reading back the spilled data does re-grouping. Note the rows cannot
/// be grouped once spilled onto disk, the read back data needs to be re-grouped again. In addition,
/// re-grouping may cause out of memory again. Thus, re-grouping has to be a sort based aggregation.
///
/// ```text
/// Partial Aggregation [batch_size = 2] (max memory = 3 rows)
///
///  INPUTS        PARTIALLY AGGREGATED (UPDATE BATCH)   OUTPUTS
/// ┌─────────┐    ┌─────────────────┐                  ┌─────────────────┐
/// │ a │ b   │    │ a │    AVG(b)   │                  │ a │    AVG(b)   │
/// │---│-----│    │   │[count]│[sum]│                  │   │[count]│[sum]│
/// │ 3 │ 3.0 │ ─▶ │---│-------│-----│                  │---│-------│-----│
/// │ 2 │ 2.0 │    │ 2 │ 1     │ 2.0 │ ─▶ early emit ─▶ │ 2 │ 1     │ 2.0 │
/// └─────────┘    │ 3 │ 2     │ 7.0 │               │  │ 3 │ 2     │ 7.0 │
/// ┌─────────┐ ─▶ │ 4 │ 1     │ 8.0 │               │  └─────────────────┘
/// │ 3 │ 4.0 │    └─────────────────┘               └▶ ┌─────────────────┐
/// │ 4 │ 8.0 │    ┌─────────────────┐                  │ 4 │ 1     │ 8.0 │
/// └─────────┘    │ a │    AVG(b)   │               ┌▶ │ 1 │ 1     │ 1.0 │
/// ┌─────────┐    │---│-------│-----│               │  └─────────────────┘
/// │ 1 │ 1.0 │ ─▶ │ 1 │ 1     │ 1.0 │ ─▶ early emit ─▶ ┌─────────────────┐
/// │ 3 │ 2.0 │    │ 3 │ 1     │ 2.0 │                  │ 3 │ 1     │ 2.0 │
/// └─────────┘    └─────────────────┘                  └─────────────────┘
///
///
/// Final Aggregation [batch_size = 2] (max memory = 3 rows)
///
/// PARTIALLY INPUTS       FINAL AGGREGATION (MERGE BATCH)       RE-GROUPED (SORTED)
/// ┌─────────────────┐    [keep using the partial schema]       [Real final aggregation
/// │ a │    AVG(b)   │    ┌─────────────────┐                    output]
/// │   │[count]│[sum]│    │ a │    AVG(b)   │                   ┌────────────┐
/// │---│-------│-----│ ─▶ │   │[count]│[sum]│                   │ a │ AVG(b) │
/// │ 3 │ 3     │ 3.0 │    │---│-------│-----│ ─▶ spill ─┐       │---│--------│
/// │ 2 │ 2     │ 1.0 │    │ 2 │ 2     │ 1.0 │           │       │ 1 │    4.0 │
/// └─────────────────┘    │ 3 │ 4     │ 8.0 │           ▼       │ 2 │    1.0 │
/// ┌─────────────────┐ ─▶ │ 4 │ 1     │ 7.0 │     Streaming  ─▶ └────────────┘
/// │ 3 │ 1     │ 5.0 │    └─────────────────┘     merge sort ─▶ ┌────────────┐
/// │ 4 │ 1     │ 7.0 │    ┌─────────────────┐            ▲      │ a │ AVG(b) │
/// └─────────────────┘    │ a │    AVG(b)   │            │      │---│--------│
/// ┌─────────────────┐    │---│-------│-----│ ─▶ memory ─┘      │ 3 │    2.0 │
/// │ 1 │ 2     │ 8.0 │ ─▶ │ 1 │ 2     │ 8.0 │                   │ 4 │    7.0 │
/// │ 2 │ 2     │ 3.0 │    │ 2 │ 2     │ 3.0 │                   └────────────┘
/// └─────────────────┘    └─────────────────┘
/// ```
pub(crate) struct GroupedHashAggregateStream {
    schema: SchemaRef,
    input: SendableRecordBatchStream,
    mode: AggregateMode,

    /// Accumulators, one for each `AggregateExpr` in the query
    ///
    /// For example, if the query has aggregates, `SUM(x)`,
    /// `COUNT(y)`, there will be two accumulators, each one
    /// specialized for that particular aggregate and its input types
    accumulators: Vec<Box<dyn GroupsAccumulator>>,

    /// Arguments to pass to each accumulator.
    ///
    /// The arguments in `accumulator[i]` is passed `aggregate_arguments[i]`
    ///
    /// The argument to each accumulator is itself a `Vec` because
    /// some aggregates such as `CORR` can accept more than one
    /// argument.
    aggregate_arguments: Vec<Vec<Arc<dyn PhysicalExpr>>>,

    /// Optional filter expression to evaluate, one for each for
    /// accumulator. If present, only those rows for which the filter
    /// evaluate to true should be included in the aggregate results.
    ///
    /// For example, for an aggregate like `SUM(x) FILTER (WHERE x >= 100)`,
    /// the filter expression is  `x > 100`.
    filter_expressions: Vec<Option<Arc<dyn PhysicalExpr>>>,

    /// GROUP BY expressions
    group_by: PhysicalGroupBy,

    /// The memory reservation for this grouping
    reservation: MemoryReservation,

    /// An interning store of group keys
    group_values: Box<dyn GroupValues>,

    /// scratch space for the current input [`RecordBatch`] being
    /// processed. Reused across batches here to avoid reallocations
    current_group_indices: Vec<usize>,

    /// Tracks if this stream is generating input or output
    exec_state: ExecutionState,

    /// Execution metrics
    baseline_metrics: BaselineMetrics,

    /// max rows in output RecordBatches
    batch_size: usize,

    /// Optional ordering information, that might allow groups to be
    /// emitted from the hash table prior to seeing the end of the
    /// input
    group_ordering: GroupOrdering,

    /// Have we seen the end of the input
    input_done: bool,

    /// The [`RuntimeEnv`] associated with the [`TaskContext`] argument
    runtime: Arc<RuntimeEnv>,

    /// The spill state object
    spill_state: SpillState,

    /// Optional soft limit on the number of `group_values` in a batch
    /// If the number of `group_values` in a single batch exceeds this value,
    /// the `GroupedHashAggregateStream` operation immediately switches to
    /// output mode and emits all groups.
    group_values_soft_limit: Option<usize>,
}

impl GroupedHashAggregateStream {
    /// Create a new GroupedHashAggregateStream
    pub fn new(
        agg: &AggregateExec,
        context: Arc<TaskContext>,
        partition: usize,
    ) -> Result<Self> {
        debug!("Creating GroupedHashAggregateStream");
        let agg_schema = Arc::clone(&agg.schema);
        let agg_group_by = agg.group_by.clone();
        let agg_filter_expr = agg.filter_expr.clone();

        let batch_size = context.session_config().batch_size();
        let input = agg.input.execute(partition, Arc::clone(&context))?;
        let baseline_metrics = BaselineMetrics::new(&agg.metrics, partition);

        let timer = baseline_metrics.elapsed_compute().timer();

        let aggregate_exprs = agg.aggr_expr.clone();

        // arguments for each aggregate, one vec of expressions per
        // aggregate
        let aggregate_arguments = aggregates::aggregate_expressions(
            &agg.aggr_expr,
            &agg.mode,
            agg_group_by.expr.len(),
        )?;
        // arguments for aggregating spilled data is the same as the one for final aggregation
        let merging_aggregate_arguments = aggregates::aggregate_expressions(
            &agg.aggr_expr,
            &AggregateMode::Final,
            agg_group_by.expr.len(),
        )?;

        let filter_expressions = match agg.mode {
            AggregateMode::Partial
            | AggregateMode::Single
            | AggregateMode::SinglePartitioned => agg_filter_expr,
            AggregateMode::Final | AggregateMode::FinalPartitioned => {
                vec![None; agg.aggr_expr.len()]
            }
        };

        // Instantiate the accumulators
        let accumulators: Vec<_> = aggregate_exprs
            .iter()
            .map(create_group_accumulator)
            .collect::<Result<_>>()?;

        let group_schema = group_schema(&agg_schema, agg_group_by.expr.len());
        let spill_expr = group_schema
            .fields
            .into_iter()
            .enumerate()
            .map(|(idx, field)| PhysicalSortExpr {
                expr: Arc::new(Column::new(field.name().as_str(), idx)) as _,
                options: SortOptions::default(),
            })
            .collect();

        let name = format!("GroupedHashAggregateStream[{partition}]");
        let reservation = MemoryConsumer::new(name)
            .with_can_spill(true)
            .register(context.memory_pool());
        let (ordering, _) = agg
            .properties()
            .equivalence_properties()
            .find_longest_permutation(&agg_group_by.output_exprs());
        let group_ordering = GroupOrdering::try_new(
            &group_schema,
            &agg.input_order_mode,
            ordering.as_slice(),
        )?;

        let group_values = new_group_values(group_schema)?;
        timer.done();

        let exec_state = ExecutionState::ReadingInput;

        let spill_state = SpillState {
            spills: vec![],
            spill_expr,
            spill_schema: agg_schema.clone(),
            is_stream_merging: false,
            merging_aggregate_arguments,
            merging_group_by: PhysicalGroupBy::new_single(agg_group_by.expr.clone()),
        };

        Ok(GroupedHashAggregateStream {
            schema: agg_schema,
            input,
            mode: agg.mode,
            accumulators,
            aggregate_arguments,
            filter_expressions,
            group_by: agg_group_by,
            reservation,
            group_values,
            current_group_indices: Default::default(),
            exec_state,
            baseline_metrics,
            batch_size,
            group_ordering,
            input_done: false,
            runtime: context.runtime_env(),
            spill_state,
            group_values_soft_limit: agg.limit,
        })
    }
}

/// Create an accumulator for `agg_expr` -- a [`GroupsAccumulator`] if
/// that is supported by the aggregate, or a
/// [`GroupsAccumulatorAdapter`] if not.
pub(crate) fn create_group_accumulator(
    agg_expr: &Arc<dyn AggregateExpr>,
) -> Result<Box<dyn GroupsAccumulator>> {
    if agg_expr.groups_accumulator_supported() {
        agg_expr.create_groups_accumulator()
    } else {
        // Note in the log when the slow path is used
        debug!(
            "Creating GroupsAccumulatorAdapter for {}: {agg_expr:?}",
            agg_expr.name()
        );
        let agg_expr_captured = agg_expr.clone();
        let factory = move || agg_expr_captured.create_accumulator();
        Ok(Box::new(GroupsAccumulatorAdapter::new(factory)))
    }
}

/// Extracts a successful Ok(_) or returns Poll::Ready(Some(Err(e))) with errors
macro_rules! extract_ok {
    ($RES: expr) => {{
        match $RES {
            Ok(v) => v,
            Err(e) => return Poll::Ready(Some(Err(e))),
        }
    }};
}

impl Stream for GroupedHashAggregateStream {
    type Item = Result<RecordBatch>;

    fn poll_next(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Self::Item>> {
        let elapsed_compute = self.baseline_metrics.elapsed_compute().clone();

        loop {
            match &self.exec_state {
                ExecutionState::ReadingInput => 'reading_input: {
                    match ready!(self.input.poll_next_unpin(cx)) {
                        // new batch to aggregate
                        Some(Ok(batch)) => {
                            let timer = elapsed_compute.timer();
                            // Make sure we have enough capacity for `batch`, otherwise spill
                            extract_ok!(self.spill_previous_if_necessary(&batch));

                            // Do the grouping
                            extract_ok!(self.group_aggregate_batch(batch));

                            // If we can begin emitting rows, do so,
                            // otherwise keep consuming input
                            assert!(!self.input_done);

                            // If the number of group values equals or exceeds the soft limit,
                            // emit all groups and switch to producing output
                            if self.hit_soft_group_limit() {
                                timer.done();
                                extract_ok!(self.set_input_done_and_produce_output());
                                // make sure the exec_state just set is not overwritten below
                                break 'reading_input;
                            }

                            if let Some(to_emit) = self.group_ordering.emit_to() {
                                let batch = extract_ok!(self.emit(to_emit, false));
                                self.exec_state = ExecutionState::ProducingOutput(batch);
                                timer.done();
                                // make sure the exec_state just set is not overwritten below
                                break 'reading_input;
                            }

                            extract_ok!(self.emit_early_if_necessary());

                            timer.done();
                        }
                        Some(Err(e)) => {
                            // inner had error, return to caller
                            return Poll::Ready(Some(Err(e)));
                        }
                        None => {
                            // inner is done, emit all rows and switch to producing output
                            extract_ok!(self.set_input_done_and_produce_output());
                        }
                    }
                }

                ExecutionState::ProducingOutput(batch) => {
                    // slice off a part of the batch, if needed
                    let output_batch;
                    let size = self.batch_size;
                    (self.exec_state, output_batch) = if batch.num_rows() <= size {
                        (
                            if self.input_done {
                                ExecutionState::Done
                            } else {
                                ExecutionState::ReadingInput
                            },
                            batch.clone(),
                        )
                    } else {
                        // output first batch_size rows
                        let size = self.batch_size;
                        let num_remaining = batch.num_rows() - size;
                        let remaining = batch.slice(size, num_remaining);
                        let output = batch.slice(0, size);
                        (ExecutionState::ProducingOutput(remaining), output)
                    };
                    return Poll::Ready(Some(Ok(
                        output_batch.record_output(&self.baseline_metrics)
                    )));
                }

                ExecutionState::Done => {
                    // release the memory reservation since sending back output batch itself needs
                    // some memory reservation, so make some room for it.
                    self.clear_all();
                    let _ = self.update_memory_reservation();
                    return Poll::Ready(None);
                }
            }
        }
    }
}

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

impl GroupedHashAggregateStream {
    /// Perform group-by aggregation for the given [`RecordBatch`].
    fn group_aggregate_batch(&mut self, batch: RecordBatch) -> Result<()> {
        // Evaluate the grouping expressions
        let group_by_values = if self.spill_state.is_stream_merging {
            evaluate_group_by(&self.spill_state.merging_group_by, &batch)?
        } else {
            evaluate_group_by(&self.group_by, &batch)?
        };

        // Evaluate the aggregation expressions.
        let input_values = if self.spill_state.is_stream_merging {
            evaluate_many(&self.spill_state.merging_aggregate_arguments, &batch)?
        } else {
            evaluate_many(&self.aggregate_arguments, &batch)?
        };

        // Evaluate the filter expressions, if any, against the inputs
        let filter_values = if self.spill_state.is_stream_merging {
            let filter_expressions = vec![None; self.accumulators.len()];
            evaluate_optional(&filter_expressions, &batch)?
        } else {
            evaluate_optional(&self.filter_expressions, &batch)?
        };

        for group_values in &group_by_values {
            // calculate the group indices for each input row
            let starting_num_groups = self.group_values.len();
            self.group_values
                .intern(group_values, &mut self.current_group_indices)?;
            let group_indices = &self.current_group_indices;

            // Update ordering information if necessary
            let total_num_groups = self.group_values.len();
            if total_num_groups > starting_num_groups {
                self.group_ordering.new_groups(
                    group_values,
                    group_indices,
                    total_num_groups,
                )?;
            }

            // Gather the inputs to call the actual accumulator
            let t = self
                .accumulators
                .iter_mut()
                .zip(input_values.iter())
                .zip(filter_values.iter());

            for ((acc, values), opt_filter) in t {
                let opt_filter = opt_filter.as_ref().map(|filter| filter.as_boolean());

                // Call the appropriate method on each aggregator with
                // the entire input row and the relevant group indexes
                match self.mode {
                    AggregateMode::Partial
                    | AggregateMode::Single
                    | AggregateMode::SinglePartitioned
                        if !self.spill_state.is_stream_merging =>
                    {
                        acc.update_batch(
                            values,
                            group_indices,
                            opt_filter,
                            total_num_groups,
                        )?;
                    }
                    _ => {
                        // if aggregation is over intermediate states,
                        // use merge
                        acc.merge_batch(
                            values,
                            group_indices,
                            opt_filter,
                            total_num_groups,
                        )?;
                    }
                }
            }
        }

        match self.update_memory_reservation() {
            // Here we can ignore `insufficient_capacity_err` because we will spill later,
            // but at least one batch should fit in the memory
            Err(DataFusionError::ResourcesExhausted(_))
                if self.group_values.len() >= self.batch_size =>
            {
                Ok(())
            }
            other => other,
        }
    }

    fn update_memory_reservation(&mut self) -> Result<()> {
        let acc = self.accumulators.iter().map(|x| x.size()).sum::<usize>();
        self.reservation.try_resize(
            acc + self.group_values.size()
                + self.group_ordering.size()
                + self.current_group_indices.allocated_size(),
        )
    }

    /// Create an output RecordBatch with the group keys and
    /// accumulator states/values specified in emit_to
    fn emit(&mut self, emit_to: EmitTo, spilling: bool) -> Result<RecordBatch> {
        let schema = if spilling {
            self.spill_state.spill_schema.clone()
        } else {
            self.schema()
        };
        if self.group_values.is_empty() {
            return Ok(RecordBatch::new_empty(schema));
        }

        let mut output = self.group_values.emit(emit_to)?;
        if let EmitTo::First(n) = emit_to {
            self.group_ordering.remove_groups(n);
        }

        // Next output each aggregate value
        for acc in self.accumulators.iter_mut() {
            match self.mode {
                AggregateMode::Partial => output.extend(acc.state(emit_to)?),
                _ if spilling => {
                    // If spilling, output partial state because the spilled data will be
                    // merged and re-evaluated later.
                    output.extend(acc.state(emit_to)?)
                }
                AggregateMode::Final
                | AggregateMode::FinalPartitioned
                | AggregateMode::Single
                | AggregateMode::SinglePartitioned => output.push(acc.evaluate(emit_to)?),
            }
        }

        // emit reduces the memory usage. Ignore Err from update_memory_reservation. Even if it is
        // over the target memory size after emission, we can emit again rather than returning Err.
        let _ = self.update_memory_reservation();
        let batch = RecordBatch::try_new(schema, output)?;
        Ok(batch)
    }

    /// Optimistically, [`Self::group_aggregate_batch`] allows to exceed the memory target slightly
    /// (~ 1 [`RecordBatch`]) for simplicity. In such cases, spill the data to disk and clear the
    /// memory. Currently only [`GroupOrdering::None`] is supported for spilling.
    fn spill_previous_if_necessary(&mut self, batch: &RecordBatch) -> Result<()> {
        // TODO: support group_ordering for spilling
        if self.group_values.len() > 0
            && batch.num_rows() > 0
            && matches!(self.group_ordering, GroupOrdering::None)
            && !matches!(self.mode, AggregateMode::Partial)
            && !self.spill_state.is_stream_merging
            && self.update_memory_reservation().is_err()
        {
            // Use input batch (Partial mode) schema for spilling because
            // the spilled data will be merged and re-evaluated later.
            self.spill_state.spill_schema = batch.schema();
            self.spill()?;
            self.clear_shrink(batch);
        }
        Ok(())
    }

    /// Emit all rows, sort them, and store them on disk.
    fn spill(&mut self) -> Result<()> {
        let emit = self.emit(EmitTo::All, true)?;
        let sorted = sort_batch(&emit, &self.spill_state.spill_expr, None)?;
        let spillfile = self.runtime.disk_manager.create_tmp_file("HashAggSpill")?;
        let mut writer = IPCWriter::new(spillfile.path(), &emit.schema())?;
        // TODO: slice large `sorted` and write to multiple files in parallel
        let mut offset = 0;
        let total_rows = sorted.num_rows();

        while offset < total_rows {
            let length = std::cmp::min(total_rows - offset, self.batch_size);
            let batch = sorted.slice(offset, length);
            offset += batch.num_rows();
            writer.write(&batch)?;
        }

        writer.finish()?;
        self.spill_state.spills.push(spillfile);
        Ok(())
    }

    /// Clear memory and shirk capacities to the size of the batch.
    fn clear_shrink(&mut self, batch: &RecordBatch) {
        self.group_values.clear_shrink(batch);
        self.current_group_indices.clear();
        self.current_group_indices.shrink_to(batch.num_rows());
    }

    /// Clear memory and shirk capacities to zero.
    fn clear_all(&mut self) {
        let s = self.schema();
        self.clear_shrink(&RecordBatch::new_empty(s));
    }

    /// Emit if the used memory exceeds the target for partial aggregation.
    /// Currently only [`GroupOrdering::None`] is supported for early emitting.
    /// TODO: support group_ordering for early emitting
    fn emit_early_if_necessary(&mut self) -> Result<()> {
        if self.group_values.len() >= self.batch_size
            && matches!(self.group_ordering, GroupOrdering::None)
            && matches!(self.mode, AggregateMode::Partial)
            && self.update_memory_reservation().is_err()
        {
            let n = self.group_values.len() / self.batch_size * self.batch_size;
            let batch = self.emit(EmitTo::First(n), false)?;
            self.exec_state = ExecutionState::ProducingOutput(batch);
        }
        Ok(())
    }

    /// At this point, all the inputs are read and there are some spills.
    /// Emit the remaining rows and create a batch.
    /// Conduct a streaming merge sort between the batch and spilled data. Since the stream is fully
    /// sorted, set `self.group_ordering` to Full, then later we can read with [`EmitTo::First`].
    fn update_merged_stream(&mut self) -> Result<()> {
        let batch = self.emit(EmitTo::All, true)?;
        // clear up memory for streaming_merge
        self.clear_all();
        self.update_memory_reservation()?;
        let mut streams: Vec<SendableRecordBatchStream> = vec![];
        let expr = self.spill_state.spill_expr.clone();
        let schema = batch.schema();
        streams.push(Box::pin(RecordBatchStreamAdapter::new(
            schema.clone(),
            futures::stream::once(futures::future::lazy(move |_| {
                sort_batch(&batch, &expr, None)
            })),
        )));
        for spill in self.spill_state.spills.drain(..) {
            let stream = read_spill_as_stream(spill, schema.clone())?;
            streams.push(stream);
        }
        self.spill_state.is_stream_merging = true;
        self.input = streaming_merge(
            streams,
            schema,
            &self.spill_state.spill_expr,
            self.baseline_metrics.clone(),
            self.batch_size,
            None,
            self.reservation.new_empty(),
        )?;
        self.input_done = false;
        self.group_ordering = GroupOrdering::Full(GroupOrderingFull::new());
        Ok(())
    }

    /// returns true if there is a soft groups limit and the number of distinct
    /// groups we have seen is over that limit
    fn hit_soft_group_limit(&self) -> bool {
        let Some(group_values_soft_limit) = self.group_values_soft_limit else {
            return false;
        };
        group_values_soft_limit <= self.group_values.len()
    }

    /// common function for signalling end of processing of the input stream
    fn set_input_done_and_produce_output(&mut self) -> Result<()> {
        self.input_done = true;
        self.group_ordering.input_done();
        let elapsed_compute = self.baseline_metrics.elapsed_compute().clone();
        let timer = elapsed_compute.timer();
        self.exec_state = if self.spill_state.spills.is_empty() {
            let batch = self.emit(EmitTo::All, false)?;
            ExecutionState::ProducingOutput(batch)
        } else {
            // If spill files exist, stream-merge them.
            self.update_merged_stream()?;
            ExecutionState::ReadingInput
        };
        timer.done();
        Ok(())
    }
}