mito2/compaction/

compactor.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::num::NonZeroU64;
use std::sync::Arc;
use std::time::Duration;

use common_base::Plugins;
use common_base::cancellation::{CancellableFuture, CancellationHandle};
use common_meta::key::SchemaMetadataManagerRef;
use common_telemetry::{debug, info, warn};
use common_time::TimeToLive;
use either::Either;
use itertools::Itertools;
use object_store::manager::ObjectStoreManagerRef;
use partition::expr::PartitionExpr;
use serde::{Deserialize, Serialize};
use snafu::{OptionExt, ResultExt};
use store_api::ManifestVersion;
use store_api::metadata::RegionMetadataRef;
use store_api::region_request::PathType;
use store_api::storage::{RegionId, SequenceNumber};

use crate::access_layer::{
    AccessLayer, AccessLayerRef, Metrics, OperationType, SstWriteRequest, WriteType,
};
use crate::cache::{CacheManager, CacheManagerRef};
use crate::compaction::picker::PickerOutput;
use crate::compaction::reader::CompactionSstReaderBuilder;
use crate::compaction::unit::CompactionUnit;
use crate::compaction::{CompactionOutput, find_dynamic_options};
use crate::config::MitoConfig;
use crate::engine::region_hook::{RegionHookRef, SstFileInfo};
use crate::error;
use crate::error::{
    EmptyRegionDirSnafu, InvalidPartitionExprSnafu, ObjectStoreNotFoundSnafu, Result,
};
use crate::manifest::action::{RegionEdit, RegionMetaAction, RegionMetaActionList};
use crate::manifest::manager::{RegionManifestManager, RegionManifestOptions};
use crate::region::options::{MergeMode, RegionOptions};
use crate::region::version::VersionRef;
use crate::region::{ManifestContext, RegionLeaderState, RegionRoleState};
use crate::schedule::scheduler::LocalScheduler;
use crate::sst::FormatType;
use crate::sst::file::{FileHandle, FileMeta, UncommittedSsts};
use crate::sst::file_purger::LocalFilePurger;
use crate::sst::index::intermediate::IntermediateManager;
use crate::sst::index::puffin_manager::PuffinManagerFactory;
use crate::sst::location::region_dir_from_table_dir;
use crate::sst::parquet::metadata::extract_primary_key_range;
use crate::sst::parquet::{SstInfo, WriteOptions};
use crate::sst::version::{SstVersion, SstVersionRef};

/// Region version for compaction that does not hold memtables.
#[derive(Clone)]
pub struct CompactionVersion {
    /// Metadata of the region.
    ///
    /// Altering metadata isn't frequent, storing metadata in Arc to allow sharing
    /// metadata and reuse metadata when creating a new `Version`.
    pub(crate) metadata: RegionMetadataRef,
    /// Options of the region.
    pub(crate) options: RegionOptions,
    /// SSTs of the region.
    pub(crate) ssts: SstVersionRef,
    /// Lower bound of pending memtable sequences from the same Version as `ssts`.
    /// None means no barrier; Some(0) conservatively represents an unknown bound.
    /// Keep only the value so background compaction cannot pin flushed memtables.
    pub(crate) memtable_min_sequence: Option<SequenceNumber>,
    /// Inferred compaction time window.
    pub(crate) compaction_time_window: Option<Duration>,
}

impl From<VersionRef> for CompactionVersion {
    fn from(value: VersionRef) -> Self {
        Self {
            metadata: value.metadata.clone(),
            options: value.options.clone(),
            ssts: value.ssts.clone(),
            memtable_min_sequence: if value.options.merge_mode() == MergeMode::LastNonNull {
                value.memtables.min_sequence()
            } else {
                None
            },
            compaction_time_window: value.compaction_time_window,
        }
    }
}

/// CompactionRegion represents a region that needs to be compacted.
/// It's the subset of MitoRegion.
#[derive(Clone)]
pub struct CompactionRegion {
    pub region_id: RegionId,
    pub region_options: RegionOptions,

    pub(crate) engine_config: Arc<MitoConfig>,
    pub(crate) region_metadata: RegionMetadataRef,
    pub(crate) cache_manager: CacheManagerRef,
    /// Access layer to get the table path and path type.
    pub access_layer: AccessLayerRef,
    pub(crate) manifest_ctx: Arc<ManifestContext>,
    pub(crate) current_version: CompactionVersion,
    pub(crate) file_purger: Option<Arc<LocalFilePurger>>,
    pub(crate) ttl: Option<TimeToLive>,

    /// Controls the parallelism of this compaction task. Default is 1.
    ///
    /// The parallel is inside this compaction task, not across different compaction tasks.
    /// It can be different windows of the same compaction task or something like this.
    pub max_parallelism: usize,

    pub(crate) plugins: Plugins,
}

/// Execution resources for compaction, without a region-wide SST snapshot.
///
/// Inputs are owned by each output or unit so a slow sibling cannot retain
/// files that another unit has already replaced.
#[derive(Clone)]
pub struct CompactionContext {
    /// Region whose files are being compacted.
    pub region_id: RegionId,
    /// Region options including resolved dynamic compaction options.
    pub region_options: RegionOptions,
    /// Options from the version used to plan the merge.
    version_options: RegionOptions,
    pub(crate) engine_config: Arc<MitoConfig>,
    region_metadata: RegionMetadataRef,
    pub(crate) cache_manager: CacheManagerRef,
    pub(crate) access_layer: AccessLayerRef,
    manifest_ctx: Arc<ManifestContext>,
    plugins: Plugins,
}

impl From<&CompactionRegion> for CompactionContext {
    fn from(region: &CompactionRegion) -> Self {
        Self {
            region_id: region.region_id,
            region_options: region.region_options.clone(),
            version_options: region.current_version.options.clone(),
            engine_config: region.engine_config.clone(),
            region_metadata: region.region_metadata.clone(),
            cache_manager: region.cache_manager.clone(),
            access_layer: region.access_layer.clone(),
            manifest_ctx: region.manifest_ctx.clone(),
            plugins: region.plugins.clone(),
        }
    }
}

/// Builds a minimal [`CompactionRegion`] for tests that do not touch the access layer.
#[cfg(test)]
pub(crate) async fn new_test_compaction_region() -> CompactionRegion {
    let env = crate::test_util::scheduler_util::SchedulerEnv::new().await;
    let metadata = crate::test_util::memtable_util::metadata_for_test();
    let manifest_ctx = env.mock_manifest_context(metadata.clone()).await;
    CompactionRegion {
        region_id: RegionId::new(1, 1),
        region_options: RegionOptions::default(),
        engine_config: Arc::new(MitoConfig::default()),
        region_metadata: metadata.clone(),
        cache_manager: Arc::new(CacheManager::default()),
        access_layer: env.access_layer.clone(),
        manifest_ctx,
        current_version: CompactionVersion {
            metadata: metadata.clone(),
            options: RegionOptions::default(),
            ssts: Arc::new(SstVersion::new(metadata)),
            memtable_min_sequence: None,
            compaction_time_window: None,
        },
        file_purger: None,
        ttl: None,
        max_parallelism: 1,
        plugins: Plugins::new(),
    }
}

/// OpenCompactionRegionRequest represents the request to open a compaction region.
#[derive(Clone)]
pub struct OpenCompactionRegionRequest {
    pub region_id: RegionId,
    pub table_dir: String,
    pub path_type: PathType,
    pub region_options: RegionOptions,
    pub max_parallelism: usize,
    /// Plugins for the compaction region, used to look up the [`RegionHook`](crate::engine::region_hook::RegionHook).
    pub plugins: Plugins,
}

/// Open a compaction region from a compaction request.
/// It's simple version of RegionOpener::open().
pub async fn open_compaction_region(
    req: &OpenCompactionRegionRequest,
    mito_config: &MitoConfig,
    object_store_manager: ObjectStoreManagerRef,
    ttl_provider: Either<TimeToLive, SchemaMetadataManagerRef>,
) -> Result<CompactionRegion> {
    let object_store = {
        let name = &req.region_options.storage;
        if let Some(name) = name {
            object_store_manager
                .find(name)
                .with_context(|| ObjectStoreNotFoundSnafu {
                    object_store: name.clone(),
                })?
        } else {
            object_store_manager.default_object_store()
        }
    };

    let access_layer = {
        let puffin_manager_factory = PuffinManagerFactory::new(
            &mito_config.index.aux_path,
            mito_config.index.staging_size.as_bytes(),
            Some(mito_config.index.write_buffer_size.as_bytes() as _),
            mito_config.index.staging_ttl,
        )
        .await?;
        let intermediate_manager =
            IntermediateManager::init_fs(mito_config.index.aux_path.clone()).await?;

        Arc::new(AccessLayer::new(
            &req.table_dir,
            req.path_type,
            object_store.clone(),
            puffin_manager_factory,
            intermediate_manager,
        ))
    };

    let manifest_manager = {
        let region_dir = region_dir_from_table_dir(&req.table_dir, req.region_id, req.path_type);
        let region_manifest_options =
            RegionManifestOptions::new(mito_config, &region_dir, object_store);

        RegionManifestManager::open(region_manifest_options, &Default::default())
            .await?
            .with_context(|| EmptyRegionDirSnafu {
                region_id: req.region_id,
                region_dir: region_dir_from_table_dir(&req.table_dir, req.region_id, req.path_type),
            })?
    };

    let manifest = manifest_manager.manifest();
    let region_metadata = manifest.metadata.clone();
    let hook: Option<RegionHookRef> = req.plugins.get();
    let manifest_ctx = Arc::new(ManifestContext::new(
        manifest_manager,
        RegionRoleState::Leader(RegionLeaderState::Writable),
        hook,
    ));

    let file_purger = {
        let purge_scheduler = Arc::new(LocalScheduler::new(mito_config.max_background_purges));
        Arc::new(LocalFilePurger::new(
            purge_scheduler.clone(),
            access_layer.clone(),
            None,
        ))
    };

    let current_version = {
        let mut ssts = SstVersion::new(region_metadata.clone());
        ssts.add_files(file_purger.clone(), manifest.files.values().cloned());
        CompactionVersion {
            metadata: region_metadata.clone(),
            options: req.region_options.clone(),
            ssts: Arc::new(ssts),
            // Remote execution uses an already picked output. A manifest-only
            // opener cannot prove that a new LastNonNull pick is memtable-safe.
            memtable_min_sequence: Some(0),
            compaction_time_window: manifest.compaction_time_window,
        }
    };

    let ttl = match ttl_provider {
        // Use the specified ttl.
        Either::Left(ttl) => ttl,
        // Get the ttl from the schema metadata manager.
        Either::Right(schema_metadata_manager) => {
            let (_, ttl) =
                find_dynamic_options(req.region_id, &req.region_options, &schema_metadata_manager)
                    .await
                    .unwrap_or_else(|e| {
                        warn!(e; "Failed to get ttl for region: {}", region_metadata.region_id);
                        (
                            crate::region::options::CompactionOptions::default(),
                            TimeToLive::default(),
                        )
                    });
            ttl
        }
    };

    Ok(CompactionRegion {
        region_id: req.region_id,
        region_options: req.region_options.clone(),
        engine_config: Arc::new(mito_config.clone()),
        region_metadata: region_metadata.clone(),
        cache_manager: Arc::new(CacheManager::default()),
        access_layer,
        manifest_ctx,
        current_version,
        file_purger: Some(file_purger),
        ttl: Some(ttl),
        max_parallelism: req.max_parallelism,
        plugins: req.plugins.clone(),
    })
}

impl CompactionRegion {
    /// Get the file purger of the compaction region.
    pub fn file_purger(&self) -> Option<Arc<LocalFilePurger>> {
        self.file_purger.clone()
    }

    /// Stop the file purger scheduler of the compaction region.
    pub async fn stop_purger_scheduler(&self) -> Result<()> {
        if let Some(file_purger) = &self.file_purger {
            file_purger.stop_scheduler().await
        } else {
            Ok(())
        }
    }

    /// Fires [`RegionHook::on_sst_files_written`] for the freshly-merged SST
    /// files in `merge_output`. Shared by both compaction paths, it must run
    /// before this unit's [`Compactor::update_manifest`] so its committed edit
    /// can be associated with the SST metadata reported here.
    pub async fn invoke_sst_hook(&self, merge_output: &MergeOutput) {
        CompactionContext::from(self)
            .invoke_sst_hook(merge_output)
            .await;
    }
}

impl CompactionContext {
    /// Reports this unit's output metadata before publishing its manifest edit.
    pub(crate) async fn invoke_sst_hook(&self, merge_output: &MergeOutput) {
        let Some(hook) = self.plugins.get::<RegionHookRef>() else {
            return;
        };

        // Remote compaction deserializes `MergeOutput` over gRPC, where
        // `sst_infos` is `#[serde(skip)]`. Rebuild each `SstInfo` from the
        // matching `FileMeta` so the hook observes real ids/rows/sizes rather
        // than zeros — see [`sst_info_from_file_meta`] for what stays default.
        let synthesized: Vec<SstInfo>;
        let infos: &[SstInfo] = if merge_output.sst_infos.is_empty() {
            synthesized = merge_output
                .files_to_add
                .iter()
                .map(sst_info_from_file_meta)
                .collect();
            &synthesized
        } else {
            // `sst_infos` and `files_to_add` are documented as 1:1. If they
            // ever diverge, `zip` below would silently truncate; warn so the
            // mismatch is observable rather than dropping files from the hook.
            if merge_output.sst_infos.len() != merge_output.files_to_add.len() {
                warn!(
                    "sst_infos length ({}) does not match files_to_add length ({}) for region {}",
                    merge_output.sst_infos.len(),
                    merge_output.files_to_add.len(),
                    self.region_id
                );
            }
            &merge_output.sst_infos
        };

        let files: Vec<SstFileInfo<'_>> = merge_output
            .files_to_add
            .iter()
            .zip(infos)
            .map(|(meta, info)| SstFileInfo {
                sst_info_ref: info,
                file_meta: meta,
            })
            .collect();
        hook.on_sst_files_written(self.region_id, &self.region_metadata, &files)
            .await;
    }

    /// Publishes outputs through the existing manifest validation and hook path.
    pub(crate) async fn update_manifest(
        &self,
        merge_output: MergeOutput,
    ) -> Result<(RegionEdit, ManifestVersion)> {
        let edit = RegionEdit {
            files_to_add: merge_output.files_to_add,
            files_to_remove: merge_output.files_to_remove,
            timestamp_ms: Some(chrono::Utc::now().timestamp_millis()),
            compaction_time_window: merge_output
                .compaction_time_window
                .map(|seconds| Duration::from_secs(seconds as u64)),
            flushed_entry_id: None,
            flushed_sequence: None,
            committed_sequence: None,
        };

        let action_list = RegionMetaActionList::with_action(RegionMetaAction::Edit(edit.clone()));
        let manifest_version = self
            .manifest_ctx
            .update_manifest_for_compaction(action_list)
            .await?;

        Ok((edit, manifest_version))
    }
}

/// Builds an [`SstInfo`] for the remote-compaction path by copying the scalar
/// fields that [`FileMeta`] also carries.
///
/// Remote compaction runs off-process and ships `MergeOutput` over the wire;
/// [`MergeOutput::sst_infos`] is `#[serde(skip)]` because the parquet footer
/// (`ParquetMetaData`) is not serde-serializable. To avoid feeding the hook
/// default (zero) values for real SSTs, this rebuilds the seven fields `FileMeta`
/// and `SstInfo` share: `file_id`, `time_range`, `file_size`,
/// `max_row_group_uncompressed_size`, `num_rows`, `num_row_groups`, `num_series`.
///
/// Two fields stay default and **cannot be recovered on the datanode**:
/// - `file_metadata` — the parquet footer, whose column min/max/null-count
///   statistics are required by hooks building richer artifacts (e.g. an Iceberg
///   manifest). That data is produced by the compactor's writer and exists only
///   in the freshly-written SST on object storage.
/// - `index_metadata` — `FileMeta` tracks indexes via `available_indexes` /
///   `indexes`, not as an [`IndexOutput`].
///
/// A hook that needs column stats must fetch the footer from object storage
/// (the [`CompactionRegion`]'s `access_layer` reaches the store), or the footer
/// must be shipped over the wire (revisit the `#[serde(skip)]` on `sst_infos`).
/// `num_rows` may read `0` for legacy `FileMeta`s where the count is unknown.
fn sst_info_from_file_meta(meta: &FileMeta) -> SstInfo {
    SstInfo {
        file_id: meta.file_id,
        time_range: meta.time_range,
        file_size: meta.file_size,
        max_row_group_uncompressed_size: meta.max_row_group_uncompressed_size,
        num_rows: meta.num_rows as usize,
        num_row_groups: meta.num_row_groups,
        num_series: meta.num_series,
        ..Default::default()
    }
}

/// `[MergeOutput]` represents the output of merging SST files.
#[derive(Default, Debug, Serialize, Deserialize)]
pub struct MergeOutput {
    pub files_to_add: Vec<FileMeta>,
    pub files_to_remove: Vec<FileMeta>,
    pub compaction_time_window: Option<i64>,
    #[serde(skip)]
    pub sst_infos: Vec<SstInfo>,
}

impl MergeOutput {
    pub fn is_empty(&self) -> bool {
        self.files_to_add.is_empty() && self.files_to_remove.is_empty()
    }

    pub fn input_file_size(&self) -> u64 {
        self.files_to_remove.iter().map(|f| f.file_size).sum()
    }

    pub fn output_file_size(&self) -> u64 {
        self.files_to_add.iter().map(|f| f.file_size).sum()
    }
}

/// Compactor is the trait that defines the compaction logic.
#[async_trait::async_trait]
pub trait Compactor: Send + Sync + 'static {
    /// Merge SST files for a region.
    async fn merge_ssts(
        &self,
        compaction_region: &CompactionRegion,
        picker_output: PickerOutput,
    ) -> Result<MergeOutput>;

    /// Update the manifest after merging SST files.
    async fn update_manifest(
        &self,
        compaction_region: &CompactionRegion,
        merge_output: MergeOutput,
    ) -> Result<(RegionEdit, ManifestVersion)>;
}

/// Trait for merging a single compaction output into SST files.
///
/// This is extracted from `DefaultCompactor` to allow injecting mock
/// implementations in tests.
#[async_trait::async_trait]
pub trait SstMerger: Send + Sync + 'static {
    async fn merge_single_output(
        &self,
        context: CompactionContext,
        output: CompactionOutput,
        write_opts: WriteOptions,
    ) -> Result<(Vec<FileMeta>, Vec<SstInfo>)>;
}

/// The production [`SstMerger`] that reads, merges, and writes SST files.
#[derive(Clone)]
pub struct DefaultSstMerger;

/// File-level sequence metadata is independent of physical row encoding.
struct OutputSequenceMetadata {
    file_sequence: Option<NonZeroU64>,
    exact_sequence_trusted: bool,
}

/// Compaction does not admit new data, so it inherits the input sequence bounds
/// without allocating a new admission marker. Retaining physical row sequences
/// does not by itself restore exact-read capability for untrusted inputs.
fn output_sequence_metadata(
    context: &CompactionContext,
    inputs: &[FileHandle],
) -> OutputSequenceMetadata {
    let exact_sequence_trusted = context.region_options.preserve_row_sequence
        && inputs
            .iter()
            .all(|f| f.is_effective_target_sequence_trusted(context.region_id));
    OutputSequenceMetadata {
        file_sequence: known_max_input_sequence(inputs),
        exact_sequence_trusted,
    }
}

/// Computes the maximum target-domain sequence bound of the output of merging
/// `inputs`. A bound can be a row maximum or an admission marker; compaction
/// must preserve both for sequence-based pruning. Unknown bounds must remain
/// unknown rather than being replaced with a partial maximum.
fn known_max_input_sequence(inputs: &[FileHandle]) -> Option<NonZeroU64> {
    let mut max: Option<NonZeroU64> = None;
    for input in inputs {
        let sequence = input.meta_ref().sequence?;
        max = Some(max.map_or(sequence, |current| current.max(sequence)));
    }
    max
}

#[async_trait::async_trait]
impl SstMerger for DefaultSstMerger {
    async fn merge_single_output(
        &self,
        context: CompactionContext,
        output: CompactionOutput,
        write_opts: WriteOptions,
    ) -> Result<(Vec<FileMeta>, Vec<SstInfo>)> {
        let region_id = context.region_id;
        let index_options = context.version_options.index_options.clone();
        let append_mode = context.version_options.append_mode;
        let merge_mode = context.version_options.merge_mode();
        let flat_format = context
            .region_options
            .sst_format
            .map(|format| format == FormatType::Flat)
            .unwrap_or(context.engine_config.default_flat_format);

        let index_config = context.engine_config.index.clone();
        let inverted_index_config = context.engine_config.inverted_index.clone();
        let fulltext_index_config = context.engine_config.fulltext_index.clone();
        let bloom_filter_index_config = context.engine_config.bloom_filter_index.clone();

        let input_file_names = output
            .inputs
            .iter()
            .map(|f| f.file_id().to_string())
            .join(",");
        let sequence_metadata = output_sequence_metadata(&context, &output.inputs);
        let builder = CompactionSstReaderBuilder {
            metadata: context.region_metadata.clone(),
            sst_layer: context.access_layer.clone(),
            cache: context.cache_manager.clone(),
            inputs: &output.inputs,
            append_mode,
            filter_deleted: output.filter_deleted,
            time_range: output.output_time_range,
            merge_mode,
        };
        let source = builder.build_flat_sst_reader().await?;

        let mut metrics = Metrics::new(WriteType::Compaction);
        let region_metadata = context.region_metadata.clone();
        let sst_infos = context
            .access_layer
            .write_sst(
                SstWriteRequest {
                    op_type: OperationType::Compact,
                    metadata: region_metadata.clone(),
                    source,
                    cache_manager: context.cache_manager.clone(),
                    // Readers resolve file overrides before merge/dedup. Replacing
                    // their effective sequences here could promote old rows above
                    // versions in SSTs that were not part of this merge.
                    max_sequence: None,
                    sst_write_format: if flat_format {
                        FormatType::Flat
                    } else {
                        FormatType::PrimaryKey
                    },
                    preserve_row_sequence: sequence_metadata.exact_sequence_trusted,
                    index_options,
                    index_config,
                    inverted_index_config,
                    fulltext_index_config,
                    bloom_filter_index_config,
                },
                &write_opts,
                &mut metrics,
            )
            .await?;
        // Convert partition expression once outside the map
        let partition_expr = match &region_metadata.partition_expr {
            None => None,
            Some(json_str) if json_str.is_empty() => None,
            Some(json_str) => PartitionExpr::from_json_str(json_str).with_context(|_| {
                InvalidPartitionExprSnafu {
                    expr: json_str.clone(),
                }
            })?,
        };

        let output_files = sst_infos
            .iter()
            .map(|sst_info| {
                let pk_range = sst_info
                    .file_metadata
                    .as_ref()
                    .and_then(|meta| extract_primary_key_range(meta, &region_metadata));
                let (primary_key_min, primary_key_max) = match pk_range {
                    Some((min, max)) => (Some(min), Some(max)),
                    None => (None, None),
                };

                FileMeta {
                    region_id,
                    file_id: sst_info.file_id,
                    time_range: sst_info.time_range,
                    level: output.output_level,
                    file_size: sst_info.file_size,
                    max_row_group_uncompressed_size: sst_info.max_row_group_uncompressed_size,
                    available_indexes: sst_info.index_metadata.build_available_indexes(),
                    indexes: sst_info.index_metadata.build_indexes(),
                    index_file_size: sst_info.index_metadata.file_size,
                    index_version: 0,
                    num_rows: sst_info.num_rows as u64,
                    num_row_groups: sst_info.num_row_groups,
                    sequence: sequence_metadata.file_sequence,
                    partition_expr: partition_expr.clone(),
                    num_series: sst_info.num_series,
                    primary_key_min,
                    primary_key_max,
                    preserve_row_sequence: sequence_metadata.exact_sequence_trusted,
                }
            })
            .collect::<Vec<_>>();
        let output_file_names = output_files.iter().map(|f| f.file_id.to_string()).join(",");
        info!(
            "Region {} compaction inputs: [{}], outputs: [{}], flat_format: {}, metrics: {:?}",
            region_id, input_file_names, output_file_names, flat_format, metrics
        );
        metrics.observe();
        Ok((output_files, sst_infos.into_iter().collect()))
    }
}

/// DefaultCompactor is the default implementation of Compactor.
///
/// It is parameterized by an [`SstMerger`] to allow injecting mock
/// implementations in tests.
pub struct DefaultCompactor<M = DefaultSstMerger> {
    merger: M,
    cancel_handle: Arc<CancellationHandle>,
    uncommitted: Option<UncommittedSsts>,
}

#[cfg(test)]
impl<M: SstMerger> DefaultCompactor<M> {
    pub fn with_merger(merger: M) -> Self {
        Self {
            merger,
            cancel_handle: Arc::new(CancellationHandle::default()),
            uncommitted: None,
        }
    }
}

impl DefaultCompactor {
    /// Creates a new `DefaultCompactor` with the given cancel handle and no
    /// uncommitted SSTs tracking.
    ///
    /// This is the public entry point for external crates that want a
    /// cancellable compactor without opting into uncommitted-SST tracking.
    pub fn new_with_cancel_handle(cancel_handle: Arc<CancellationHandle>) -> Self {
        Self {
            merger: DefaultSstMerger,
            cancel_handle,
            uncommitted: None,
        }
    }

    pub(crate) fn with_cancel_handle(
        cancel_handle: Arc<CancellationHandle>,
        uncommitted: UncommittedSsts,
    ) -> Self {
        Self {
            merger: DefaultSstMerger,
            cancel_handle,
            uncommitted: Some(uncommitted),
        }
    }
}

impl<M: SstMerger> DefaultCompactor<M> {
    /// Merges a complete atomic unit. No partial input replacement is returned.
    pub(crate) async fn merge_unit(
        &self,
        context: &CompactionContext,
        unit: &CompactionUnit,
    ) -> Result<MergeOutput> {
        let mut result = MergeOutput {
            files_to_remove: unit.inputs.iter().map(|f| f.meta_ref().clone()).collect(),
            compaction_time_window: Some(unit.time_window_size),
            ..Default::default()
        };
        for output in &unit.outputs {
            if self.cancel_handle.is_cancelled() {
                return error::CompactionCancelledSnafu.fail();
            }
            // Let the writer finish and register its files before observing cancellation.
            // Dropping it mid-write can lose ownership of already finalized SSTs.
            let (files, infos) = self
                .merger
                .merge_single_output(
                    context.clone(),
                    output.clone(),
                    WriteOptions {
                        write_buffer_size: context.engine_config.sst_write_buffer_size,
                        max_file_size: unit.max_file_size,
                        row_group_size: context.region_options.row_group_size(),
                        float_field_encoding: context.region_options.float_field_encoding,
                    },
                )
                .await?;
            if let Some(uncommitted) = &self.uncommitted {
                uncommitted.track(&infos);
            }
            result.files_to_add.extend(files);
            result.sst_infos.extend(infos);
        }
        if self.cancel_handle.is_cancelled() {
            return error::CompactionCancelledSnafu.fail();
        }
        Ok(result)
    }
}

#[async_trait::async_trait]
impl<M: SstMerger> Compactor for DefaultCompactor<M>
where
    M: Clone,
{
    async fn merge_ssts(
        &self,
        compaction_region: &CompactionRegion,
        mut picker_output: PickerOutput,
    ) -> Result<MergeOutput> {
        let internal_parallelism = compaction_region.max_parallelism.max(1);
        let compaction_time_window = picker_output.time_window_size;
        let region_id = compaction_region.region_id;
        let context = CompactionContext::from(compaction_region);

        // Build tasks along with their input file metas so we can track which
        // inputs correspond to each task.
        let mut tasks: Vec<(Vec<FileMeta>, _)> = Vec::with_capacity(picker_output.outputs.len());

        for output in picker_output.outputs.drain(..) {
            let inputs_to_remove: Vec<_> =
                output.inputs.iter().map(|f| f.meta_ref().clone()).collect();
            let write_opts = WriteOptions {
                write_buffer_size: compaction_region.engine_config.sst_write_buffer_size,
                max_file_size: picker_output.max_file_size,
                row_group_size: compaction_region.region_options.row_group_size(),
                float_field_encoding: compaction_region.region_options.float_field_encoding,
            };
            let merger = self.merger.clone();
            let context = context.clone();
            let uncommitted = self.uncommitted.clone();
            let fut = async move {
                let result = merger
                    .merge_single_output(context, output, write_opts)
                    .await;
                if let (Some(uncommitted), Ok((_, infos))) = (&uncommitted, &result) {
                    uncommitted.track(infos);
                }
                result
            };
            tasks.push((inputs_to_remove, fut));
        }

        let hook: Option<RegionHookRef> = compaction_region.plugins.get();
        let mut output_files = Vec::with_capacity(tasks.len());
        let mut all_sst_infos: Vec<SstInfo> = Vec::new();
        let mut compacted_inputs = Vec::with_capacity(
            tasks.iter().map(|(inputs, _)| inputs.len()).sum::<usize>()
                + picker_output.expired_ssts.len(),
        );

        while !tasks.is_empty() {
            let mut chunk: Vec<(Vec<FileMeta>, _)> = Vec::with_capacity(internal_parallelism);
            for _ in 0..internal_parallelism {
                if let Some(task) = tasks.pop() {
                    chunk.push(task);
                }
            }
            let mut spawned: Vec<_> = chunk
                .into_iter()
                .map(|(inputs, fut)| {
                    let handle = common_runtime::spawn_compact(fut);
                    (inputs, handle)
                })
                .collect();

            while let Some((inputs, mut handle)) = spawned.pop() {
                let abort_handle = handle.abort_handle();
                match CancellableFuture::new(&mut handle, self.cancel_handle.clone()).await {
                    Ok(Ok(Ok((files, infos)))) => {
                        output_files.extend(files);
                        if hook.is_some() {
                            all_sst_infos.extend(infos);
                        }
                        compacted_inputs.extend(inputs);
                    }
                    Ok(Ok(Err(e))) => {
                        warn!(
                            e; "Failed to merge compaction output for region: {}, inputs: [{}]",
                            region_id,
                            inputs.iter().map(|f| f.file_id.to_string()).join(",")
                        );
                    }
                    Ok(Err(e)) => {
                        warn!(
                            "Region {} compaction task join error for inputs: [{}], skipping: {}",
                            region_id,
                            inputs.iter().map(|f| f.file_id.to_string()).join(","),
                            e
                        );
                        // If the cancel handle is cancelled,
                        // cancel the remaining tasks before returns the error.
                        if self.cancel_handle.is_cancelled() {
                            abort_handle.abort();
                            for (_, handle) in &spawned {
                                handle.abort();
                            }
                            for (_, handle) in spawned {
                                let _ = handle.await;
                            }
                        }
                        return Err(e).context(error::JoinSnafu);
                    }
                    Err(_) => {
                        debug!(
                            "Compaction merge cancelled for region: {}, aborting remaining {} spawned tasks",
                            region_id,
                            spawned.len(),
                        );
                        abort_handle.abort();
                        for (_, handle) in &spawned {
                            handle.abort();
                        }
                        let _ = handle.await;
                        for (_, handle) in spawned {
                            let _ = handle.await;
                        }
                        break;
                    }
                }
            }

            if self.cancel_handle.is_cancelled() {
                info!("Compaction merge cancelled for region: {}", region_id);
                break;
            }
        }

        // Include expired SSTs in removals — these don't depend on merge success.
        compacted_inputs.extend(
            picker_output
                .expired_ssts
                .iter()
                .map(|f| f.meta_ref().clone()),
        );

        Ok(MergeOutput {
            files_to_add: output_files,
            files_to_remove: compacted_inputs,
            compaction_time_window: Some(compaction_time_window),
            sst_infos: all_sst_infos,
        })
    }

    async fn update_manifest(
        &self,
        compaction_region: &CompactionRegion,
        merge_output: MergeOutput,
    ) -> Result<(RegionEdit, ManifestVersion)> {
        CompactionContext::from(compaction_region)
            .update_manifest(merge_output)
            .await
    }
}

#[cfg(test)]
mod tests {
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::{Arc, Mutex};
    use std::time::Duration;

    use store_api::storage::{FileId, RegionId};
    use tokio::time::sleep;

    use super::{DefaultCompactor, *};
    use crate::compaction::picker::PickerOutput;
    use crate::error::Result;
    use crate::sst::file::FileHandle;
    use crate::sst::file_purger::NoopFilePurger;

    fn dummy_file_meta() -> FileMeta {
        FileMeta {
            region_id: RegionId::new(1, 1),
            file_id: FileId::random(),
            file_size: 100,
            ..Default::default()
        }
    }

    fn new_file_handle(meta: FileMeta) -> FileHandle {
        FileHandle::new(meta, Arc::new(NoopFilePurger))
    }

    #[test]
    fn test_effective_target_trust_and_max_sequence() {
        let target = RegionId::new(1, 1);
        let local_trusted = new_file_handle(FileMeta {
            region_id: target,
            sequence: NonZeroU64::new(3),
            preserve_row_sequence: true,
            ..dummy_file_meta()
        });
        let foreign_untrusted_marker = new_file_handle(FileMeta {
            region_id: RegionId::new(1, 2),
            sequence: NonZeroU64::new(9),
            preserve_row_sequence: false,
            ..dummy_file_meta()
        });
        let local_untrusted = new_file_handle(FileMeta {
            region_id: target,
            sequence: NonZeroU64::new(11),
            preserve_row_sequence: false,
            ..dummy_file_meta()
        });
        assert!(local_trusted.is_effective_target_sequence_trusted(target));
        assert!(foreign_untrusted_marker.is_effective_target_sequence_trusted(target));
        assert!(!local_untrusted.is_effective_target_sequence_trusted(target));
        assert_eq!(
            NonZeroU64::new(9),
            known_max_input_sequence(&[local_trusted, foreign_untrusted_marker])
        );
    }

    #[test]
    fn test_known_max_input_sequence() {
        let meta_with = |sequence| FileMeta {
            sequence,
            ..dummy_file_meta()
        };

        let inputs = vec![
            new_file_handle(meta_with(NonZeroU64::new(3))),
            new_file_handle(meta_with(NonZeroU64::new(9))),
            new_file_handle(meta_with(NonZeroU64::new(5))),
        ];
        assert_eq!(NonZeroU64::new(9), known_max_input_sequence(&inputs));

        let inputs = vec![
            new_file_handle(meta_with(NonZeroU64::new(9))),
            new_file_handle(meta_with(None)),
        ];
        assert_eq!(None, known_max_input_sequence(&inputs));

        assert_eq!(None, known_max_input_sequence(&[]));
    }

    #[tokio::test]
    async fn test_output_sequence_metadata_preserves_trust_and_unknown_bounds() {
        let mut region = new_test_compaction_region().await;
        let local = region.region_id;
        let foreign = RegionId::new(1, 2);
        let file = |region_id, sequence: Option<u64>, preserve_row_sequence| {
            new_file_handle(FileMeta {
                region_id,
                sequence: sequence.and_then(NonZeroU64::new),
                preserve_row_sequence,
                ..dummy_file_meta()
            })
        };
        // Bounds are independent of row trust: known, mixed trust, unknown in
        // either sequence domain, empty inputs, and the largest possible bound.
        let cases = [
            (
                vec![file(local, Some(3), true), file(foreign, Some(9), false)],
                Some(9),
                true,
            ),
            (
                vec![file(local, Some(3), true), file(local, Some(6), false)],
                Some(6),
                false,
            ),
            (
                vec![file(foreign, Some(9), false), file(foreign, Some(11), true)],
                Some(11),
                true,
            ),
            (
                vec![file(local, Some(3), true), file(local, None, true)],
                None,
                true,
            ),
            (
                vec![file(local, None, false), file(local, Some(6), true)],
                None,
                false,
            ),
            (
                vec![file(local, Some(3), true), file(foreign, None, true)],
                None,
                false,
            ),
            (vec![], None, true),
            (
                vec![file(local, Some(u64::MAX), false)],
                Some(u64::MAX),
                false,
            ),
        ];
        for committed_sequence in [100, 101] {
            region
                .manifest_ctx
                .manifest_manager
                .write()
                .await
                .update(
                    RegionMetaActionList::with_action(RegionMetaAction::Edit(RegionEdit {
                        committed_sequence: Some(committed_sequence),
                        files_to_add: vec![],
                        files_to_remove: vec![],
                        timestamp_ms: None,
                        compaction_time_window: None,
                        flushed_entry_id: None,
                        flushed_sequence: None,
                    })),
                    false,
                )
                .await
                .unwrap();
            for preserve in [false, true] {
                region.region_options.preserve_row_sequence = preserve;
                for (inputs, known_bound, inputs_trusted) in &cases {
                    let metadata =
                        output_sequence_metadata(&CompactionContext::from(&region), inputs);
                    let trusted = preserve && *inputs_trusted;
                    assert_eq!(trusted, metadata.exact_sequence_trusted);
                    assert_eq!(
                        known_bound.and_then(NonZeroU64::new),
                        metadata.file_sequence
                    );
                }
            }
        }
    }

    /// Independent outputs must be safe in either visibility order, including when
    /// only one output succeeds. Merely committing both outputs together is not a
    /// substitute for preserving version order across their separate merge streams.
    #[rstest::rstest]
    #[case(true)]
    #[case(false)]
    #[tokio::test]
    async fn test_independent_outputs_preserve_delete_in_every_visibility_state(
        #[case] flat_format: bool,
        #[values(false, true)] unknown_put_bound: bool,
    ) {
        use datatypes::arrow::array::AsArray;
        use datatypes::arrow::datatypes::TimestampMillisecondType;
        use store_api::region_engine::RegionEngine;
        use store_api::region_request::RegionRequest;

        use crate::compaction::CompactionOutput;
        use crate::compaction::compactor::{CompactionRegion, Compactor, DefaultCompactor};
        use crate::compaction::picker::PickerOutput;
        use crate::compaction::reader::CompactionSstReaderBuilder;
        use crate::engine::compaction_test::{delete_and_flush, put_and_flush};
        use crate::region::options::MergeMode;
        use crate::sst::file::FileHandle;
        use crate::sst::file_purger::NoopFilePurger;
        use crate::test_util::{CreateRequestBuilder, TestEnv, rows_schema};

        let mut env = TestEnv::new().await;
        let region_id = RegionId::new(1, 1);
        let config = MitoConfig {
            default_flat_format: flat_format,
            min_compaction_interval: Duration::from_secs(3600),
            ..Default::default()
        };
        let engine = env.create_engine(config).await;
        let request = CreateRequestBuilder::new().build();
        let columns = rows_schema(&request);
        engine
            .handle_request(region_id, RegionRequest::Create(request))
            .await
            .unwrap();
        put_and_flush(&engine, region_id, &columns, 0..1).await;
        delete_and_flush(&engine, region_id, &columns, 0..1).await;
        put_and_flush(&engine, region_id, &columns, 10..11).await;
        let region = engine.get_region(region_id).unwrap();
        let version = region.version();
        let mut files: Vec<_> = version
            .ssts
            .levels()
            .iter()
            .flat_map(|level| level.files())
            .cloned()
            .collect();
        assert_eq!(3, files.len());
        files.sort_unstable_by_key(|file| file.meta_ref().sequence);
        if unknown_put_bound {
            // Model a legacy SST whose physical rows are readable but whose
            // file-level boundary is unknown. Merging cannot invent that bound.
            let mut meta = files[0].meta_ref().clone();
            meta.sequence = None;
            files[0] = FileHandle::new(meta, Arc::new(NoopFilePurger));
        }
        let compaction_region = CompactionRegion {
            region_id,
            region_options: version.options.clone(),
            engine_config: Arc::new(MitoConfig {
                default_flat_format: flat_format,
                ..Default::default()
            }),
            region_metadata: version.metadata.clone(),
            cache_manager: engine.cache_manager(),
            access_layer: region.access_layer.clone(),
            manifest_ctx: region.manifest_ctx.clone(),
            current_version: version.into(),
            file_purger: None,
            ttl: None,
            max_parallelism: 2,
            plugins: common_base::Plugins::new(),
        };
        let puts = vec![files[0].clone(), files[2].clone()];
        let deletes = vec![files[1].clone()];
        let picker_output = PickerOutput {
            outputs: [puts.clone(), deletes.clone()]
                .into_iter()
                .map(|inputs| CompactionOutput {
                    output_level: 1,
                    inputs,
                    filter_deleted: false,
                    output_time_range: None,
                })
                .collect(),
            expired_ssts: vec![],
            time_window_size: 3600,
            max_file_size: None,
        };
        let merged = DefaultCompactor::with_merger(DefaultSstMerger)
            .merge_ssts(&compaction_region, picker_output)
            .await
            .unwrap();
        assert_eq!(2, merged.files_to_add.len());
        let outputs: Vec<_> = merged
            .files_to_add
            .into_iter()
            .map(|meta| FileHandle::new(meta, Arc::new(NoopFilePurger)))
            .collect();
        let put_output = outputs
            .iter()
            .find(|file| file.meta_ref().num_rows == 2)
            .unwrap();
        let delete_output = outputs
            .iter()
            .find(|file| file.meta_ref().num_rows == 1)
            .unwrap();
        assert_eq!(
            if unknown_put_bound {
                None
            } else {
                NonZeroU64::new(3)
            },
            put_output.meta_ref().sequence,
        );
        assert_eq!(NonZeroU64::new(2), delete_output.meta_ref().sequence);
        assert!(
            outputs
                .iter()
                .all(|file| !file.meta_ref().preserve_row_sequence)
        );

        // Cover the original snapshot, each partial success/cancellation state,
        // and both completed outputs using real persisted SSTs and merge readers.
        for (put_done, delete_done) in [(false, false), (true, false), (false, true), (true, true)]
        {
            let mut visible = if put_done {
                vec![put_output.clone()]
            } else {
                puts.clone()
            };
            visible.extend(if delete_done {
                vec![delete_output.clone()]
            } else {
                deletes.clone()
            });
            let mut reader = CompactionSstReaderBuilder {
                metadata: compaction_region.region_metadata.clone(),
                sst_layer: region.access_layer.clone(),
                cache: engine.cache_manager(),
                inputs: &visible,
                append_mode: false,
                filter_deleted: true,
                time_range: None,
                merge_mode: MergeMode::LastRow,
            }
            .build_flat_sst_reader()
            .await
            .unwrap();
            let mut timestamps = Vec::new();
            while let Some(batch) = reader.next_batch().await.unwrap() {
                timestamps.extend(
                    batch
                        .column_by_name("ts")
                        .unwrap()
                        .as_primitive::<TimestampMillisecondType>()
                        .values()
                        .iter()
                        .copied(),
                );
            }
            assert_eq!(
                vec![10_000],
                timestamps,
                "put_done={put_done}, delete_done={delete_done}"
            );
        }
    }

    /// An [`SstMerger`] that returns pre-configured results per call index.
    ///
    /// Call 0 gets `results[0]`, call 1 gets `results[1]`, etc.
    #[derive(Clone)]
    struct MockMerger {
        results: Arc<Mutex<Vec<Result<Vec<FileMeta>>>>>,
        call_idx: Arc<AtomicUsize>,
    }

    impl MockMerger {
        fn new(results: Vec<Result<Vec<FileMeta>>>) -> Self {
            Self {
                results: Arc::new(Mutex::new(results)),
                call_idx: Arc::new(AtomicUsize::new(0)),
            }
        }
    }

    #[async_trait::async_trait]
    impl SstMerger for MockMerger {
        async fn merge_single_output(
            &self,
            _context: CompactionContext,
            _output: CompactionOutput,
            _write_opts: WriteOptions,
        ) -> Result<(Vec<FileMeta>, Vec<SstInfo>)> {
            let idx = self.call_idx.fetch_add(1, Ordering::SeqCst);
            match self.results.lock().unwrap().get(idx) {
                Some(Ok(files)) => Ok((files.clone(), Vec::new())),
                Some(Err(_)) => error::InvalidMetaSnafu {
                    reason: format!("simulated failure at index {idx}"),
                }
                .fail(),
                None => panic!("MockMerger: no result configured for call index {idx}"),
            }
        }
    }

    #[tokio::test]
    async fn test_compaction_unit_group_failure_is_atomic() {
        let context = CompactionContext::from(&new_test_compaction_region().await);
        let input = new_file_handle(dummy_file_meta());
        let unit = CompactionUnit::from_picker(PickerOutput {
            outputs: (0..2)
                .map(|_| CompactionOutput {
                    output_level: 1,
                    inputs: vec![input.clone()],
                    filter_deleted: false,
                    output_time_range: None,
                })
                .collect(),
            ..Default::default()
        })
        .unwrap()
        .pop()
        .unwrap();
        for fail_second in [false, true] {
            let second = if fail_second {
                error::InvalidMetaSnafu {
                    reason: "second output failed",
                }
                .fail()
            } else {
                Ok(vec![dummy_file_meta(), dummy_file_meta()])
            };
            let compactor =
                DefaultCompactor::with_merger(MockMerger::new(vec![Ok(Vec::new()), second]));
            let result = compactor.merge_unit(&context, &unit).await;
            if fail_second {
                assert!(
                    result.is_err(),
                    "cannot publish a successful subset of a dependency group"
                );
            } else {
                let result = result.unwrap();
                assert_eq!(2, result.files_to_add.len());
                assert_eq!(
                    vec![input.meta_ref().file_id],
                    result
                        .files_to_remove
                        .iter()
                        .map(|f| f.file_id)
                        .collect::<Vec<_>>()
                );
            }
        }
    }

    #[tokio::test]
    async fn test_partial_merge_failure_collects_only_successful_outputs() {
        common_telemetry::init_default_ut_logging();

        let compaction_region = new_test_compaction_region().await;

        // Prepare 3 compaction outputs: output 0 and 2 succeed, output 1 fails.
        let input_meta_0 = dummy_file_meta();
        let input_meta_1 = dummy_file_meta();
        let input_meta_2 = dummy_file_meta();

        let output_meta_0 = vec![dummy_file_meta()];
        let output_meta_2 = vec![dummy_file_meta(), dummy_file_meta()];

        let merger = MockMerger::new(vec![
            Ok(output_meta_0.clone()),
            Err(error::InvalidMetaSnafu {
                reason: "boom".to_string(),
            }
            .build()),
            Ok(output_meta_2.clone()),
        ]);
        let compactor = DefaultCompactor::with_merger(merger);

        let picker_output = PickerOutput {
            outputs: vec![
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(input_meta_0.clone())],
                    filter_deleted: false,
                    output_time_range: None,
                },
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(input_meta_1.clone())],
                    filter_deleted: false,
                    output_time_range: None,
                },
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(input_meta_2.clone())],
                    filter_deleted: false,
                    output_time_range: None,
                },
            ],
            expired_ssts: vec![],
            time_window_size: 3600,
            max_file_size: None,
        };

        let merge_output = compactor
            .merge_ssts(&compaction_region, picker_output)
            .await
            .unwrap();

        // Outputs 0 and 2 succeeded (1 + 2 = 3 files added).
        assert_eq!(merge_output.files_to_add.len(), 3);
        // Only inputs from successful merges should be removed.
        assert_eq!(merge_output.files_to_remove.len(), 2);

        let removed_ids: Vec<_> = merge_output
            .files_to_remove
            .iter()
            .map(|f| f.file_id)
            .collect();
        assert!(removed_ids.contains(&input_meta_0.file_id));
        assert!(removed_ids.contains(&input_meta_2.file_id));
        // The failed output's input must NOT be removed.
        assert!(!removed_ids.contains(&input_meta_1.file_id));
    }

    #[tokio::test]
    async fn test_all_outputs_succeed() {
        common_telemetry::init_default_ut_logging();

        let compaction_region = new_test_compaction_region().await;
        let input_meta = dummy_file_meta();
        let output_meta = vec![dummy_file_meta()];

        let merger = MockMerger::new(vec![Ok(output_meta.clone())]);
        let compactor = DefaultCompactor::with_merger(merger);

        let picker_output = PickerOutput {
            outputs: vec![CompactionOutput {
                output_level: 1,
                inputs: vec![new_file_handle(input_meta.clone())],
                filter_deleted: false,
                output_time_range: None,
            }],
            expired_ssts: vec![],
            time_window_size: 3600,
            max_file_size: None,
        };

        let merge_output = compactor
            .merge_ssts(&compaction_region, picker_output)
            .await
            .unwrap();

        assert_eq!(merge_output.files_to_add.len(), 1);
        assert_eq!(merge_output.files_to_add[0].file_id, output_meta[0].file_id);
        assert_eq!(merge_output.files_to_remove.len(), 1);
        assert_eq!(merge_output.files_to_remove[0].file_id, input_meta.file_id);
    }

    #[tokio::test]
    async fn test_expired_ssts_always_removed() {
        common_telemetry::init_default_ut_logging();

        let compaction_region = new_test_compaction_region().await;
        let input_meta = dummy_file_meta();
        let expired_meta = dummy_file_meta();

        // The single merge output fails, but expired SSTs should still be removed.
        let merger = MockMerger::new(vec![Err(error::InvalidMetaSnafu {
            reason: "fail".to_string(),
        }
        .build())]);
        let compactor = DefaultCompactor::with_merger(merger);

        let picker_output = PickerOutput {
            outputs: vec![CompactionOutput {
                output_level: 1,
                inputs: vec![new_file_handle(input_meta.clone())],
                filter_deleted: false,
                output_time_range: None,
            }],
            expired_ssts: vec![new_file_handle(expired_meta.clone())],
            time_window_size: 3600,
            max_file_size: None,
        };

        let merge_output = compactor
            .merge_ssts(&compaction_region, picker_output)
            .await
            .unwrap();

        // No files added (merge failed).
        assert!(merge_output.files_to_add.is_empty());
        // Only the expired SST should be in files_to_remove (not the failed merge's input).
        assert_eq!(merge_output.files_to_remove.len(), 1);
        assert_eq!(
            merge_output.files_to_remove[0].file_id,
            expired_meta.file_id
        );
    }

    #[derive(Clone)]
    struct BlockingMerger {
        call_idx: Arc<AtomicUsize>,
    }

    #[async_trait::async_trait]
    impl SstMerger for BlockingMerger {
        async fn merge_single_output(
            &self,
            _context: CompactionContext,
            _output: CompactionOutput,
            _write_opts: WriteOptions,
        ) -> Result<(Vec<FileMeta>, Vec<SstInfo>)> {
            self.call_idx.fetch_add(1, Ordering::SeqCst);
            std::future::pending().await
        }
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn test_merge_ssts_cancels_spawned_tasks() {
        common_telemetry::init_default_ut_logging();

        let mut compaction_region = new_test_compaction_region().await;
        compaction_region.max_parallelism = 2;

        let cancel_handle = Arc::new(CancellationHandle::default());
        let call_idx = Arc::new(AtomicUsize::new(0));
        let compactor = DefaultCompactor {
            merger: BlockingMerger {
                call_idx: call_idx.clone(),
            },
            cancel_handle: cancel_handle.clone(),
            uncommitted: None,
        };

        let picker_output = PickerOutput {
            outputs: vec![
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(dummy_file_meta())],
                    filter_deleted: false,
                    output_time_range: None,
                },
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(dummy_file_meta())],
                    filter_deleted: false,
                    output_time_range: None,
                },
                CompactionOutput {
                    output_level: 1,
                    inputs: vec![new_file_handle(dummy_file_meta())],
                    filter_deleted: false,
                    output_time_range: None,
                },
            ],
            expired_ssts: vec![],
            time_window_size: 3600,
            max_file_size: None,
        };

        let task = tokio::spawn(async move {
            compactor
                .merge_ssts(&compaction_region, picker_output)
                .await
        });

        sleep(Duration::from_millis(100)).await;
        cancel_handle.cancel();

        let merge_output = task
            .await
            .expect("merge_ssts should stop after cancellation")
            .unwrap();

        let started = call_idx.load(Ordering::SeqCst);

        assert!(merge_output.files_to_add.is_empty());
        assert!(merge_output.files_to_remove.is_empty());
        assert_eq!(started, 2);
    }
}