assign partition_ranges

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>

src/mito2/src/error.rs

@@ -710,8 +710,8 @@ pub enum Error {
         error: std::io::Error,
     },
 
-    #[snafu(display("Failed to filter record batch"))]
+    #[snafu(display("Record batch error"))]
-    FilterRecordBatch {
+    RecordBatch {
         source: common_recordbatch::error::Error,
         #[snafu(implicit)]
         location: Location,
@@ -1021,6 +1021,20 @@ pub enum Error {
         #[snafu(implicit)]
         location: Location,
     },
+
+    #[snafu(display("Failed to scan series"))]
+    ScanSeries {
+        #[snafu(implicit)]
+        location: Location,
+        source: Arc<Error>,
+    },
+
+    #[snafu(display("Partition {} scan multiple times", partition))]
+    ScanMultiTimes {
+        partition: usize,
+        #[snafu(implicit)]
+        location: Location,
+    },
 }
 
 pub type Result<T, E = Error> = std::result::Result<T, E>;
@@ -1143,7 +1157,7 @@ impl ErrorExt for Error {
 
             External { source, .. } => source.status_code(),
 
-            FilterRecordBatch { source, .. } => source.status_code(),
+            RecordBatch { source, .. } => source.status_code(),
 
             Download { .. } | Upload { .. } => StatusCode::StorageUnavailable,
             ChecksumMismatch { .. } => StatusCode::Unexpected,
@@ -1172,6 +1186,10 @@ impl ErrorExt for Error {
             ManualCompactionOverride {} => StatusCode::Cancelled,
 
             IncompatibleWalProviderChange { .. } => StatusCode::InvalidArguments,
+
+            ScanSeries { source, .. } => source.status_code(),
+
+            ScanMultiTimes { .. } => StatusCode::InvalidArguments,
         }
     }
 

src/mito2/src/read.rs

@@ -24,6 +24,7 @@ pub(crate) mod range;
 pub(crate) mod scan_region;
 pub(crate) mod scan_util;
 pub(crate) mod seq_scan;
+pub(crate) mod series_scan;
 pub(crate) mod unordered_scan;
 
 use std::collections::{HashMap, HashSet};

src/mito2/src/read/prune.rs

@@ -21,7 +21,7 @@ use datatypes::arrow::array::BooleanArray;
 use datatypes::arrow::buffer::BooleanBuffer;
 use snafu::ResultExt;
 
-use crate::error::{FilterRecordBatchSnafu, Result};
+use crate::error::{RecordBatchSnafu, Result};
 use crate::memtable::BoxedBatchIterator;
 use crate::read::last_row::RowGroupLastRowCachedReader;
 use crate::read::{Batch, BatchReader};
@@ -201,7 +201,7 @@ impl PruneTimeIterator {
             for filter in filters.iter() {
                 let result = filter
                     .evaluate_vector(batch.timestamps())
-                    .context(FilterRecordBatchSnafu)?;
+                    .context(RecordBatchSnafu)?;
                 mask = mask.bitand(&result);
             }
 

src/mito2/src/read/scan_region.rs

@@ -46,6 +46,7 @@ use crate::read::compat::{self, CompatBatch};
 use crate::read::projection::ProjectionMapper;
 use crate::read::range::{FileRangeBuilder, MemRangeBuilder, RangeMeta, RowGroupIndex};
 use crate::read::seq_scan::SeqScan;
+use crate::read::series_scan::SeriesScan;
 use crate::read::unordered_scan::UnorderedScan;
 use crate::read::{Batch, Source};
 use crate::region::options::MergeMode;
@@ -66,6 +67,8 @@ pub(crate) enum Scanner {
     Seq(SeqScan),
     /// Unordered scan.
     Unordered(UnorderedScan),
+    /// Per-series scan.
+    Series(SeriesScan),
 }
 
 impl Scanner {
@@ -75,6 +78,7 @@ impl Scanner {
         match self {
             Scanner::Seq(seq_scan) => seq_scan.build_stream(),
             Scanner::Unordered(unordered_scan) => unordered_scan.build_stream().await,
+            Scanner::Series(series_scan) => series_scan.build_stream().await,
         }
     }
 }
@@ -86,6 +90,7 @@ impl Scanner {
         match self {
             Scanner::Seq(seq_scan) => seq_scan.input().num_files(),
             Scanner::Unordered(unordered_scan) => unordered_scan.input().num_files(),
+            Scanner::Series(series_scan) => series_scan.input().num_files(),
         }
     }
 
@@ -94,6 +99,7 @@ impl Scanner {
         match self {
             Scanner::Seq(seq_scan) => seq_scan.input().num_memtables(),
             Scanner::Unordered(unordered_scan) => unordered_scan.input().num_memtables(),
+            Scanner::Series(series_scan) => series_scan.input().num_memtables(),
         }
     }
 
@@ -102,6 +108,7 @@ impl Scanner {
         match self {
             Scanner::Seq(seq_scan) => seq_scan.input().file_ids(),
             Scanner::Unordered(unordered_scan) => unordered_scan.input().file_ids(),
+            Scanner::Series(series_scan) => series_scan.input().file_ids(),
         }
     }
 
@@ -113,6 +120,7 @@ impl Scanner {
         match self {
             Scanner::Seq(seq_scan) => seq_scan.prepare(request).unwrap(),
             Scanner::Unordered(unordered_scan) => unordered_scan.prepare(request).unwrap(),
+            Scanner::Series(series_scan) => series_scan.prepare(request).unwrap(),
         }
     }
 }
@@ -248,7 +256,9 @@ impl ScanRegion {
 
     /// Returns a [Scanner] to scan the region.
     pub(crate) fn scanner(self) -> Result<Scanner> {
-        if self.use_unordered_scan() {
+        if self.use_series_scan() {
+            self.series_scan().map(Scanner::Series)
+        } else if self.use_unordered_scan() {
             // If table is append only and there is no series row selector, we use unordered scan in query.
             // We still use seq scan in compaction.
             self.unordered_scan().map(Scanner::Unordered)
@@ -260,7 +270,9 @@ impl ScanRegion {
     /// Returns a [RegionScanner] to scan the region.
     #[tracing::instrument(level = tracing::Level::DEBUG, skip_all)]
     pub(crate) fn region_scanner(self) -> Result<RegionScannerRef> {
-        if self.use_unordered_scan() {
+        if self.use_series_scan() {
+            self.series_scan().map(|scanner| Box::new(scanner) as _)
+        } else if self.use_unordered_scan() {
             self.unordered_scan().map(|scanner| Box::new(scanner) as _)
         } else {
             self.seq_scan().map(|scanner| Box::new(scanner) as _)
@@ -279,6 +291,12 @@ impl ScanRegion {
         Ok(UnorderedScan::new(input))
     }
 
+    /// Scans by series.
+    pub(crate) fn series_scan(self) -> Result<SeriesScan> {
+        let input = self.scan_input(true)?;
+        Ok(SeriesScan::new(input))
+    }
+
     #[cfg(test)]
     pub(crate) fn scan_without_filter_deleted(self) -> Result<SeqScan> {
         let input = self.scan_input(false)?;
@@ -299,6 +317,11 @@ impl ScanRegion {
                 || self.request.distribution == Some(TimeSeriesDistribution::TimeWindowed))
     }
 
+    /// Returns true if the region can use series scan for current request.
+    fn use_series_scan(&self) -> bool {
+        self.request.distribution == Some(TimeSeriesDistribution::PerSeries)
+    }
+
     /// Creates a scan input.
     fn scan_input(mut self, filter_deleted: bool) -> Result<ScanInput> {
         let time_range = self.build_time_range_predicate();

src/mito2/src/read/seq_scan.rs

@@ -30,7 +30,7 @@ use datatypes::schema::SchemaRef;
 use snafu::ResultExt;
 use store_api::metadata::RegionMetadataRef;
 use store_api::region_engine::{PartitionRange, PrepareRequest, RegionScanner, ScannerProperties};
-use store_api::storage::{TimeSeriesDistribution, TimeSeriesRowSelector};
+use store_api::storage::TimeSeriesRowSelector;
 use tokio::sync::Semaphore;
 
 use crate::error::{PartitionOutOfRangeSnafu, Result};
@@ -149,7 +149,7 @@ impl SeqScan {
     /// Builds a reader to read sources. If `semaphore` is provided, reads sources in parallel
     /// if possible.
     #[tracing::instrument(level = tracing::Level::DEBUG, skip_all)]
-    async fn build_reader_from_sources(
+    pub(crate) async fn build_reader_from_sources(
         stream_ctx: &StreamContext,
         mut sources: Vec<Source>,
         semaphore: Option<Arc<Semaphore>>,
@@ -207,10 +207,6 @@ impl SeqScan {
             ));
         }
 
-        if self.stream_ctx.input.distribution == Some(TimeSeriesDistribution::PerSeries) {
-            return self.scan_partition_by_series(metrics_set, partition);
-        }
-
         let stream_ctx = self.stream_ctx.clone();
         let semaphore = self.new_semaphore();
         let partition_ranges = self.properties.partitions[partition].clone();
@@ -237,14 +233,14 @@ impl SeqScan {
                     &mut sources,
                 );
 
+                let mut metrics = ScannerMetrics::default();
+                let mut fetch_start = Instant::now();
                 let mut reader =
                     Self::build_reader_from_sources(&stream_ctx, sources, semaphore.clone())
                         .await
                         .map_err(BoxedError::new)
                         .context(ExternalSnafu)?;
                 let cache = &stream_ctx.input.cache_strategy;
-                let mut metrics = ScannerMetrics::default();
-                let mut fetch_start = Instant::now();
                 #[cfg(debug_assertions)]
                 let mut checker = crate::read::BatchChecker::default()
                     .with_start(Some(part_range.start))
@@ -307,97 +303,6 @@ impl SeqScan {
         Ok(stream)
     }
 
-    /// Scans all ranges in the given partition and merge by time series.
-    /// Otherwise the returned stream might not contains any data.
-    fn scan_partition_by_series(
-        &self,
-        metrics_set: &ExecutionPlanMetricsSet,
-        partition: usize,
-    ) -> Result<SendableRecordBatchStream, BoxedError> {
-        let stream_ctx = self.stream_ctx.clone();
-        let semaphore = self.new_semaphore();
-        let partition_ranges = self.properties.partitions[partition].clone();
-        let distinguish_range = self.properties.distinguish_partition_range;
-        let part_metrics = self.new_partition_metrics(metrics_set, partition);
-        debug_assert!(!self.compaction);
-
-        let stream = try_stream! {
-            part_metrics.on_first_poll();
-
-            let range_builder_list = Arc::new(RangeBuilderList::new(
-                stream_ctx.input.num_memtables(),
-                stream_ctx.input.num_files(),
-            ));
-            // Scans all parts.
-            let mut sources = Vec::with_capacity(partition_ranges.len());
-            for part_range in partition_ranges {
-                build_sources(
-                    &stream_ctx,
-                    &part_range,
-                    false,
-                    &part_metrics,
-                    range_builder_list.clone(),
-                    &mut sources,
-                );
-            }
-
-            // Builds a reader that merge sources from all parts.
-            let mut reader =
-                Self::build_reader_from_sources(&stream_ctx, sources, semaphore.clone())
-                    .await
-                    .map_err(BoxedError::new)
-                    .context(ExternalSnafu)?;
-            let cache = &stream_ctx.input.cache_strategy;
-            let mut metrics = ScannerMetrics::default();
-            let mut fetch_start = Instant::now();
-
-            while let Some(batch) = reader
-                .next_batch()
-                .await
-                .map_err(BoxedError::new)
-                .context(ExternalSnafu)?
-            {
-                metrics.scan_cost += fetch_start.elapsed();
-                metrics.num_batches += 1;
-                metrics.num_rows += batch.num_rows();
-
-                debug_assert!(!batch.is_empty());
-                if batch.is_empty() {
-                    continue;
-                }
-
-                let convert_start = Instant::now();
-                let record_batch = stream_ctx.input.mapper.convert(&batch, cache)?;
-                metrics.convert_cost += convert_start.elapsed();
-                let yield_start = Instant::now();
-                yield record_batch;
-                metrics.yield_cost += yield_start.elapsed();
-
-                fetch_start = Instant::now();
-            }
-
-            // Yields an empty part to indicate this range is terminated.
-            // The query engine can use this to optimize some queries.
-            if distinguish_range {
-                let yield_start = Instant::now();
-                yield stream_ctx.input.mapper.empty_record_batch();
-                metrics.yield_cost += yield_start.elapsed();
-            }
-
-            metrics.scan_cost += fetch_start.elapsed();
-            part_metrics.merge_metrics(&metrics);
-
-            part_metrics.on_finish();
-        };
-
-        let stream = Box::pin(RecordBatchStreamWrapper::new(
-            self.stream_ctx.input.mapper.output_schema(),
-            Box::pin(stream),
-        ));
-
-        Ok(stream)
-    }
-
     fn new_semaphore(&self) -> Option<Arc<Semaphore>> {
         if self.properties.target_partitions() > self.properties.num_partitions() {
             // We can use additional tasks to read the data if we have more target partitions than actual partitions.
@@ -498,7 +403,7 @@ impl fmt::Debug for SeqScan {
 }
 
 /// Builds sources for the partition range and push them to the `sources` vector.
-fn build_sources(
+pub(crate) fn build_sources(
     stream_ctx: &Arc<StreamContext>,
     part_range: &PartitionRange,
     compaction: bool,
@@ -509,8 +414,8 @@ fn build_sources(
     // Gets range meta.
     let range_meta = &stream_ctx.ranges[part_range.identifier];
     #[cfg(debug_assertions)]
-    if compaction || stream_ctx.input.distribution == Some(TimeSeriesDistribution::PerSeries) {
+    if compaction {
-        // Compaction or per series distribution expects input sources are not been split.
+        // Compaction expects input sources are not been split.
         debug_assert_eq!(range_meta.indices.len(), range_meta.row_group_indices.len());
         for (i, row_group_idx) in range_meta.row_group_indices.iter().enumerate() {
             // It should scan all row groups.

src/mito2/src/read/series_scan.rs

@@ -0,0 +1,496 @@
+// 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.
+
+//! Per-series scan implementation.
+
+use std::fmt;
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+use async_stream::{stream, try_stream};
+use common_error::ext::BoxedError;
+use common_recordbatch::error::ExternalSnafu;
+use common_recordbatch::{RecordBatch, RecordBatchStreamWrapper, SendableRecordBatchStream};
+use datafusion::physical_plan::metrics::ExecutionPlanMetricsSet;
+use datafusion::physical_plan::{DisplayAs, DisplayFormatType};
+use datatypes::compute::concat_batches;
+use datatypes::schema::SchemaRef;
+use futures::StreamExt;
+use smallvec::{smallvec, SmallVec};
+use snafu::{ensure, OptionExt, ResultExt};
+use store_api::metadata::RegionMetadataRef;
+use store_api::region_engine::{PartitionRange, PrepareRequest, RegionScanner, ScannerProperties};
+use tokio::sync::mpsc::error::SendTimeoutError;
+use tokio::sync::mpsc::{self, Receiver, Sender};
+use tokio::sync::Semaphore;
+
+use crate::error::{
+    ComputeArrowSnafu, Error, InvalidSenderSnafu, PartitionOutOfRangeSnafu, Result,
+    ScanMultiTimesSnafu, ScanSeriesSnafu,
+};
+use crate::read::range::RangeBuilderList;
+use crate::read::scan_region::{ScanInput, StreamContext};
+use crate::read::scan_util::PartitionMetrics;
+use crate::read::seq_scan::{build_sources, SeqScan};
+use crate::read::{Batch, ScannerMetrics};
+
+/// Timeout to send a batch to a sender.
+const SEND_TIMEOUT: Duration = Duration::from_millis(100);
+
+/// List of receivers.
+type ReceiverList = Vec<Option<Receiver<Result<SeriesBatch>>>>;
+
+/// Scans a region and returns sorted rows of a series in the same partition.
+///
+/// The output order is always order by `(primary key, time index)` inside every
+/// partition.
+/// Always returns the same series (primary key) to the same partition.
+pub struct SeriesScan {
+    /// Properties of the scanner.
+    properties: ScannerProperties,
+    /// Context of streams.
+    stream_ctx: Arc<StreamContext>,
+    /// Receivers of each partition.
+    receivers: Mutex<ReceiverList>,
+}
+
+impl SeriesScan {
+    /// Creates a new [SeriesScan].
+    pub(crate) fn new(input: ScanInput) -> Self {
+        let mut properties = ScannerProperties::default()
+            .with_append_mode(input.append_mode)
+            .with_total_rows(input.total_rows());
+        let stream_ctx = Arc::new(StreamContext::seq_scan_ctx(input, false));
+        properties.partitions = vec![stream_ctx.partition_ranges()];
+
+        Self {
+            properties,
+            stream_ctx,
+            receivers: Mutex::new(Vec::new()),
+        }
+    }
+
+    fn scan_partition_impl(
+        &self,
+        metrics_set: &ExecutionPlanMetricsSet,
+        partition: usize,
+    ) -> Result<SendableRecordBatchStream, BoxedError> {
+        if partition >= self.properties.num_partitions() {
+            return Err(BoxedError::new(
+                PartitionOutOfRangeSnafu {
+                    given: partition,
+                    all: self.properties.num_partitions(),
+                }
+                .build(),
+            ));
+        }
+
+        self.maybe_start_distributor(metrics_set);
+
+        let part_metrics = new_partition_metrics(&self.stream_ctx, metrics_set, partition);
+        let mut receiver = self.take_receiver(partition).map_err(BoxedError::new)?;
+        let stream_ctx = self.stream_ctx.clone();
+
+        let stream = try_stream! {
+            part_metrics.on_first_poll();
+
+            let cache = &stream_ctx.input.cache_strategy;
+            let mut df_record_batches = Vec::new();
+            let mut metrics = ScannerMetrics::default();
+            let mut fetch_start = Instant::now();
+            while let Some(result) = receiver.recv().await {
+                let series = result.map_err(BoxedError::new).context(ExternalSnafu)?;
+
+                let convert_start = Instant::now();
+                df_record_batches.reserve(series.batches.len());
+                for batch in series.batches {
+                    metrics.scan_cost += fetch_start.elapsed();
+                    metrics.num_batches += 1;
+                    metrics.num_rows += batch.num_rows();
+
+                    let record_batch = stream_ctx.input.mapper.convert(&batch, cache)?;
+                    df_record_batches.push(record_batch.into_df_record_batch());
+                }
+
+                let output_schema = stream_ctx.input.mapper.output_schema();
+                let df_record_batch =
+                    concat_batches(output_schema.arrow_schema(), &df_record_batches)
+                        .context(ComputeArrowSnafu)
+                        .map_err(BoxedError::new)
+                        .context(ExternalSnafu)?;
+                df_record_batches.clear();
+                let record_batch =
+                    RecordBatch::try_from_df_record_batch(output_schema, df_record_batch)?;
+                metrics.convert_cost += convert_start.elapsed();
+
+                let yield_start = Instant::now();
+                yield record_batch;
+                metrics.yield_cost += yield_start.elapsed();
+
+                metrics.scan_cost += fetch_start.elapsed();
+                part_metrics.merge_metrics(&metrics);
+                fetch_start = Instant::now();
+            }
+        };
+
+        let stream = Box::pin(RecordBatchStreamWrapper::new(
+            self.stream_ctx.input.mapper.output_schema(),
+            Box::pin(stream),
+        ));
+
+        Ok(stream)
+    }
+
+    /// Takes the receiver for the partition.
+    fn take_receiver(&self, partition: usize) -> Result<Receiver<Result<SeriesBatch>>> {
+        let mut rx_list = self.receivers.lock().unwrap();
+        rx_list[partition]
+            .take()
+            .context(ScanMultiTimesSnafu { partition })
+    }
+
+    /// Starts the distributor if the receiver list is empty.
+    fn maybe_start_distributor(&self, metrics_set: &ExecutionPlanMetricsSet) {
+        let mut rx_list = self.receivers.lock().unwrap();
+        if !rx_list.is_empty() {
+            return;
+        }
+
+        let (senders, receivers) = new_channel_list(self.properties.num_partitions());
+        let mut distributor = SeriesDistributor {
+            stream_ctx: self.stream_ctx.clone(),
+            semaphore: Some(Arc::new(Semaphore::new(self.properties.num_partitions()))),
+            partitions: self.properties.partitions.clone(),
+            senders,
+            metrics_set: metrics_set.clone(),
+        };
+        common_runtime::spawn_global(async move {
+            distributor.execute().await;
+        });
+
+        *rx_list = receivers;
+    }
+
+    // TODO(yingwen): Reuse codes.
+    /// Scans the region and returns a stream.
+    pub(crate) async fn build_stream(&self) -> Result<SendableRecordBatchStream, BoxedError> {
+        let part_num = self.properties.num_partitions();
+        let metrics_set = ExecutionPlanMetricsSet::default();
+        let streams = (0..part_num)
+            .map(|i| self.scan_partition(&metrics_set, i))
+            .collect::<Result<Vec<_>, BoxedError>>()?;
+        let stream = stream! {
+            for mut stream in streams {
+                while let Some(rb) = stream.next().await {
+                    yield rb;
+                }
+            }
+        };
+        let stream = Box::pin(RecordBatchStreamWrapper::new(
+            self.schema(),
+            Box::pin(stream),
+        ));
+        Ok(stream)
+    }
+}
+
+fn new_channel_list(num_partitions: usize) -> (SenderList, ReceiverList) {
+    let (senders, receivers): (Vec<_>, Vec<_>) = (0..num_partitions)
+        .map(|_| {
+            let (sender, receiver) = mpsc::channel(1);
+            (Some(sender), Some(receiver))
+        })
+        .unzip();
+    (SenderList::new(senders), receivers)
+}
+
+impl RegionScanner for SeriesScan {
+    fn properties(&self) -> &ScannerProperties {
+        &self.properties
+    }
+
+    fn schema(&self) -> SchemaRef {
+        self.stream_ctx.input.mapper.output_schema()
+    }
+
+    fn metadata(&self) -> RegionMetadataRef {
+        self.stream_ctx.input.mapper.metadata().clone()
+    }
+
+    fn scan_partition(
+        &self,
+        metrics_set: &ExecutionPlanMetricsSet,
+        partition: usize,
+    ) -> Result<SendableRecordBatchStream, BoxedError> {
+        self.scan_partition_impl(metrics_set, partition)
+    }
+
+    fn prepare(&mut self, request: PrepareRequest) -> Result<(), BoxedError> {
+        self.properties.prepare(request);
+        Ok(())
+    }
+
+    fn has_predicate(&self) -> bool {
+        let predicate = self.stream_ctx.input.predicate();
+        predicate.map(|p| !p.exprs().is_empty()).unwrap_or(false)
+    }
+
+    fn set_logical_region(&mut self, logical_region: bool) {
+        self.properties.set_logical_region(logical_region);
+    }
+}
+
+impl DisplayAs for SeriesScan {
+    fn fmt_as(&self, t: DisplayFormatType, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "SeriesScan: region={}, ",
+            self.stream_ctx.input.mapper.metadata().region_id
+        )?;
+        match t {
+            DisplayFormatType::Default => self.stream_ctx.format_for_explain(false, f),
+            DisplayFormatType::Verbose => self.stream_ctx.format_for_explain(true, f),
+        }
+    }
+}
+
+impl fmt::Debug for SeriesScan {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SeriesScan")
+            .field("num_ranges", &self.stream_ctx.ranges.len())
+            .finish()
+    }
+}
+
+#[cfg(test)]
+impl SeriesScan {
+    /// Returns the input.
+    pub(crate) fn input(&self) -> &ScanInput {
+        &self.stream_ctx.input
+    }
+}
+
+/// The distributor scans series and distributes them to different partitions.
+struct SeriesDistributor {
+    /// Context for the scan stream.
+    stream_ctx: Arc<StreamContext>,
+    /// Optional semaphore for limiting the number of concurrent scans.
+    semaphore: Option<Arc<Semaphore>>,
+    /// Partition ranges to scan.
+    partitions: Vec<Vec<PartitionRange>>,
+    /// Senders of all partitions.
+    senders: SenderList,
+    /// Metrics set to report.
+    /// The distributor report the metrics as an addtional partition.
+    /// This may double the scan cost of the [SeriesScan] metrics. We can
+    /// get per-partition metrics in verbose mode to see the metrics of the
+    /// distributor.
+    metrics_set: ExecutionPlanMetricsSet,
+}
+
+impl SeriesDistributor {
+    /// Executes the distributor.
+    async fn execute(&mut self) {
+        if let Err(e) = self.scan_partitions().await {
+            self.senders.send_error(e).await;
+        }
+    }
+
+    /// Scans all parts.
+    async fn scan_partitions(&mut self) -> Result<()> {
+        let part_metrics =
+            new_partition_metrics(&self.stream_ctx, &self.metrics_set, self.partitions.len());
+        part_metrics.on_first_poll();
+
+        let range_builder_list = Arc::new(RangeBuilderList::new(
+            self.stream_ctx.input.num_memtables(),
+            self.stream_ctx.input.num_files(),
+        ));
+        // Scans all parts.
+        let mut sources = Vec::with_capacity(self.partitions.len());
+        for partition in &self.partitions {
+            sources.reserve(partition.len());
+            for part_range in partition {
+                build_sources(
+                    &self.stream_ctx,
+                    &part_range,
+                    false,
+                    &part_metrics,
+                    range_builder_list.clone(),
+                    &mut sources,
+                );
+            }
+        }
+
+        // Builds a reader that merge sources from all parts.
+        let mut reader =
+            SeqScan::build_reader_from_sources(&self.stream_ctx, sources, self.semaphore.clone())
+                .await?;
+        let mut metrics = ScannerMetrics::default();
+        let mut fetch_start = Instant::now();
+
+        let mut current_series = SeriesBatch::default();
+        while let Some(batch) = reader.next_batch().await? {
+            metrics.scan_cost += fetch_start.elapsed();
+            metrics.num_batches += 1;
+            metrics.num_rows += batch.num_rows();
+
+            debug_assert!(!batch.is_empty());
+            if batch.is_empty() {
+                continue;
+            }
+
+            let Some(last_key) = current_series.current_key() else {
+                current_series.push(batch);
+                continue;
+            };
+
+            if last_key == batch.primary_key() {
+                current_series.push(batch);
+                continue;
+            }
+
+            // We find a new series, send the current one.
+            let to_send = std::mem::replace(&mut current_series, SeriesBatch::single(batch));
+            let yield_start = Instant::now();
+            self.senders.send_batch(to_send).await?;
+            metrics.yield_cost += yield_start.elapsed();
+
+            fetch_start = Instant::now();
+        }
+
+        // todo: if not empty
+        if !current_series.is_empty() {
+            let yield_start = Instant::now();
+            self.senders.send_batch(current_series).await?;
+            metrics.yield_cost += yield_start.elapsed();
+        }
+
+        metrics.scan_cost += fetch_start.elapsed();
+        part_metrics.merge_metrics(&metrics);
+
+        part_metrics.on_finish();
+
+        Ok(())
+    }
+}
+
+/// Batches of the same series.
+#[derive(Default)]
+struct SeriesBatch {
+    batches: SmallVec<[Batch; 4]>,
+}
+
+impl SeriesBatch {
+    /// Creates a new [SeriesBatch] from a single [Batch].
+    fn single(batch: Batch) -> Self {
+        Self {
+            batches: smallvec![batch],
+        }
+    }
+
+    fn current_key(&self) -> Option<&[u8]> {
+        self.batches.first().map(|batch| batch.primary_key())
+    }
+
+    fn push(&mut self, batch: Batch) {
+        self.batches.push(batch);
+    }
+
+    /// Returns true if there is no batch.
+    fn is_empty(&self) -> bool {
+        self.batches.is_empty()
+    }
+}
+
+/// List of senders.
+struct SenderList {
+    senders: Vec<Option<Sender<Result<SeriesBatch>>>>,
+    /// Number of None senders.
+    num_nones: usize,
+    /// Index of the current partition to send.
+    sender_idx: usize,
+}
+
+impl SenderList {
+    fn new(senders: Vec<Option<Sender<Result<SeriesBatch>>>>) -> Self {
+        let num_nones = senders.iter().filter(|sender| sender.is_none()).count();
+        Self {
+            senders,
+            num_nones,
+            sender_idx: 0,
+        }
+    }
+
+    /// Finds a partition and sends the batch to the partition.
+    async fn send_batch(&mut self, mut batch: SeriesBatch) -> Result<()> {
+        loop {
+            ensure!(self.num_nones < self.senders.len(), InvalidSenderSnafu);
+
+            let sender_idx = self.fetch_add_sender_idx();
+            let Some(sender) = &self.senders[sender_idx] else {
+                continue;
+            };
+            // Adds a timeout to avoid blocking indefinitely and sending
+            // the batch in a round-robin fashion when some partitions
+            // don't poll their inputs. This may happen if we have a
+            // node like sort merging. But it is rare when we are using SeriesScan.
+            match sender.send_timeout(Ok(batch), SEND_TIMEOUT).await {
+                Ok(()) => break,
+                Err(SendTimeoutError::Timeout(res)) => {
+                    // Safety: we send Ok.
+                    batch = res.unwrap();
+                }
+                Err(SendTimeoutError::Closed(res)) => {
+                    self.senders[sender_idx] = None;
+                    self.num_nones += 1;
+                    // Safety: we send Ok.
+                    batch = res.unwrap();
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    async fn send_error(&self, error: Error) {
+        let error = Arc::new(error);
+        for sender in &self.senders {
+            if let Some(sender) = sender {
+                let result = Err(error.clone()).context(ScanSeriesSnafu);
+                let _ = sender.send(result).await;
+            }
+        }
+    }
+
+    fn fetch_add_sender_idx(&mut self) -> usize {
+        let sender_idx = self.sender_idx;
+        self.sender_idx = (self.sender_idx + 1) % self.senders.len();
+        sender_idx
+    }
+}
+
+fn new_partition_metrics(
+    stream_ctx: &StreamContext,
+    metrics_set: &ExecutionPlanMetricsSet,
+    partition: usize,
+) -> PartitionMetrics {
+    PartitionMetrics::new(
+        stream_ctx.input.mapper.metadata().region_id,
+        partition,
+        "SeriesScan",
+        stream_ctx.query_start,
+        metrics_set,
+    )
+}

src/mito2/src/sst/parquet/file_range.rs

@@ -27,7 +27,7 @@ use snafu::{OptionExt, ResultExt};
 use store_api::storage::TimeSeriesRowSelector;
 
 use crate::error::{
-    DecodeStatsSnafu, FieldTypeMismatchSnafu, FilterRecordBatchSnafu, Result, StatsNotPresentSnafu,
+    DecodeStatsSnafu, FieldTypeMismatchSnafu, RecordBatchSnafu, Result, StatsNotPresentSnafu,
 };
 use crate::read::compat::CompatBatch;
 use crate::read::last_row::RowGroupLastRowCachedReader;
@@ -286,7 +286,7 @@ impl RangeBase {
                     if filter
                         .filter()
                         .evaluate_scalar(&pk_value)
-                        .context(FilterRecordBatchSnafu)?
+                        .context(RecordBatchSnafu)?
                     {
                         continue;
                     } else {
@@ -303,12 +303,12 @@ impl RangeBase {
                     filter
                         .filter()
                         .evaluate_vector(field_col)
-                        .context(FilterRecordBatchSnafu)?
+                        .context(RecordBatchSnafu)?
                 }
                 SemanticType::Timestamp => filter
                     .filter()
                     .evaluate_vector(input.timestamps())
-                    .context(FilterRecordBatchSnafu)?,
+                    .context(RecordBatchSnafu)?,
             };
 
             mask = mask.bitand(&result);

src/query/src/optimizer/parallelize_scan.rs

@@ -62,6 +62,7 @@ impl ParallelizeScan {
                 } else if let Some(region_scan_exec) =
                     plan.as_any().downcast_ref::<RegionScanExec>()
                 {
+                    let expected_partition_num = config.execution.target_partitions;
                     if region_scan_exec.is_partition_set() {
                         return Ok(Transformed::no(plan));
                     }
@@ -71,12 +72,17 @@ impl ParallelizeScan {
                         region_scan_exec.distribution(),
                         Some(TimeSeriesDistribution::PerSeries)
                     ) {
-                        return Ok(Transformed::no(plan));
+                        let partition_range = region_scan_exec.get_partition_ranges();
+                        let mut new_partitions = vec![vec![]; expected_partition_num];
+                        new_partitions[0] = partition_range;
+                        let new_plan = region_scan_exec
+                            .with_new_partitions(new_partitions, expected_partition_num)
+                            .map_err(|e| DataFusionError::External(e.into_inner()))?;
+                        return Ok(Transformed::yes(Arc::new(new_plan)));
                     }
 
                     let ranges = region_scan_exec.get_partition_ranges();
                     let total_range_num = ranges.len();
-                    let expected_partition_num = config.execution.target_partitions;
 
                     // assign ranges to each partition
                     let mut partition_ranges =