feat: pre-download the ingested sst (GreptimeTeam#4636)

* refactor: pre-read the ingested sst file in object store to fill the local cache to accelerate first query

* feat: pre-download the ingested SST from remote to accelerate following reads

* resolve PR comments

* resolve PR comments

src/mito2/src/cache/write_cache.rs

@@ -27,7 +27,10 @@ use snafu::ResultExt;
 use crate::access_layer::{new_fs_cache_store, SstWriteRequest};
 use crate::cache::file_cache::{FileCache, FileCacheRef, FileType, IndexKey, IndexValue};
 use crate::error::{self, Result};
-use crate::metrics::{FLUSH_ELAPSED, UPLOAD_BYTES_TOTAL};
+use crate::metrics::{
+    FLUSH_ELAPSED, UPLOAD_BYTES_TOTAL, WRITE_CACHE_DOWNLOAD_BYTES_TOTAL,
+    WRITE_CACHE_DOWNLOAD_ELAPSED,
+};
 use crate::sst::index::intermediate::IntermediateManager;
 use crate::sst::index::puffin_manager::PuffinManagerFactory;
 use crate::sst::index::IndexerBuilder;
@@ -166,6 +169,79 @@ impl WriteCache {
         Ok(Some(sst_info))
     }
 
+    /// Downloads a file in `remote_path` from the remote object store to the local cache
+    /// (specified by `index_key`).
+    pub(crate) async fn download(
+        &self,
+        index_key: IndexKey,
+        remote_path: &str,
+        remote_store: &ObjectStore,
+    ) -> Result<()> {
+        const DOWNLOAD_READER_CONCURRENCY: usize = 8;
+        const DOWNLOAD_READER_CHUNK_SIZE: ReadableSize = ReadableSize::mb(8);
+
+        let file_type = index_key.file_type;
+        let timer = WRITE_CACHE_DOWNLOAD_ELAPSED
+            .with_label_values(&[match file_type {
+                FileType::Parquet => "download_parquet",
+                FileType::Puffin => "download_puffin",
+            }])
+            .start_timer();
+
+        let remote_metadata = remote_store
+            .stat(remote_path)
+            .await
+            .context(error::OpenDalSnafu)?;
+        let reader = remote_store
+            .reader_with(remote_path)
+            .concurrent(DOWNLOAD_READER_CONCURRENCY)
+            .chunk(DOWNLOAD_READER_CHUNK_SIZE.as_bytes() as usize)
+            .await
+            .context(error::OpenDalSnafu)?
+            .into_futures_async_read(0..remote_metadata.content_length())
+            .await
+            .context(error::OpenDalSnafu)?;
+
+        let cache_path = self.file_cache.cache_file_path(index_key);
+        let mut writer = self
+            .file_cache
+            .local_store()
+            .writer(&cache_path)
+            .await
+            .context(error::OpenDalSnafu)?
+            .into_futures_async_write();
+
+        let region_id = index_key.region_id;
+        let file_id = index_key.file_id;
+        let bytes_written =
+            futures::io::copy(reader, &mut writer)
+                .await
+                .context(error::DownloadSnafu {
+                    region_id,
+                    file_id,
+                    file_type,
+                })?;
+        writer.close().await.context(error::DownloadSnafu {
+            region_id,
+            file_id,
+            file_type,
+        })?;
+
+        WRITE_CACHE_DOWNLOAD_BYTES_TOTAL.inc_by(bytes_written);
+
+        let elapsed = timer.stop_and_record();
+        debug!(
+            "Successfully download file '{}' to local '{}', file size: {}, region: {}, cost: {:?}s",
+            remote_path, cache_path, bytes_written, region_id, elapsed,
+        );
+
+        let index_value = IndexValue {
+            file_size: bytes_written as _,
+        };
+        self.file_cache.put(index_key, index_value).await;
+        Ok(())
+    }
+
     /// Uploads a Parquet file or a Puffin file to the remote object store.
     async fn upload(
         &self,

src/mito2/src/engine/edit_region_test.rs

@@ -12,21 +12,96 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
 
 use object_store::ObjectStore;
 use store_api::region_engine::RegionEngine;
 use store_api::region_request::RegionRequest;
 use store_api::storage::RegionId;
-use tokio::sync::Barrier;
+use tokio::sync::{oneshot, Barrier};
 
 use crate::config::MitoConfig;
+use crate::engine::listener::EventListener;
 use crate::engine::MitoEngine;
 use crate::manifest::action::RegionEdit;
 use crate::region::MitoRegionRef;
 use crate::sst::file::{FileId, FileMeta};
 use crate::test_util::{CreateRequestBuilder, TestEnv};
 
+#[tokio::test]
+async fn test_edit_region_fill_cache() {
+    let mut env = TestEnv::new();
+
+    struct EditRegionListener {
+        tx: Mutex<Option<oneshot::Sender<FileId>>>,
+    }
+
+    impl EventListener for EditRegionListener {
+        fn on_file_cache_filled(&self, file_id: FileId) {
+            let mut tx = self.tx.lock().unwrap();
+            tx.take().unwrap().send(file_id).unwrap();
+        }
+    }
+
+    let (tx, rx) = oneshot::channel();
+    let engine = env
+        .create_engine_with(
+            MitoConfig {
+                // Write cache must be enabled to download the ingested SST file.
+                enable_experimental_write_cache: true,
+                ..Default::default()
+            },
+            None,
+            Some(Arc::new(EditRegionListener {
+                tx: Mutex::new(Some(tx)),
+            })),
+        )
+        .await;
+
+    let region_id = RegionId::new(1, 1);
+    engine
+        .handle_request(
+            region_id,
+            RegionRequest::Create(CreateRequestBuilder::new().build()),
+        )
+        .await
+        .unwrap();
+    let region = engine.get_region(region_id).unwrap();
+
+    let file_id = FileId::random();
+    // Simulating the ingestion of an SST file.
+    env.get_object_store()
+        .unwrap()
+        .write(
+            &format!("{}/{}.parquet", region.region_dir(), file_id),
+            b"x".as_slice(),
+        )
+        .await
+        .unwrap();
+
+    let edit = RegionEdit {
+        files_to_add: vec![FileMeta {
+            region_id: region.region_id,
+            file_id,
+            level: 0,
+            ..Default::default()
+        }],
+        files_to_remove: vec![],
+        compaction_time_window: None,
+        flushed_entry_id: None,
+        flushed_sequence: None,
+    };
+    engine.edit_region(region.region_id, edit).await.unwrap();
+
+    // Asserts that the background downloading of the SST is succeeded.
+    let actual = tokio::time::timeout(Duration::from_secs(9), rx)
+        .await
+        .unwrap()
+        .unwrap();
+    assert_eq!(file_id, actual);
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 4)]
 async fn test_edit_region_concurrently() {
     const EDITS_PER_TASK: usize = 10;

src/mito2/src/engine/listener.rs

@@ -22,6 +22,8 @@ use common_telemetry::info;
 use store_api::storage::RegionId;
 use tokio::sync::Notify;
 
+use crate::sst::file::FileId;
+
 /// Mito engine background event listener.
 #[async_trait]
 pub trait EventListener: Send + Sync {
@@ -61,6 +63,9 @@ pub trait EventListener: Send + Sync {
     fn on_recv_requests(&self, request_num: usize) {
         let _ = request_num;
     }
+
+    /// Notifies the listener that the file cache is filled when, for example, editing region.
+    fn on_file_cache_filled(&self, _file_id: FileId) {}
 }
 
 pub type EventListenerRef = Arc<dyn EventListener>;

src/mito2/src/error.rs

@@ -639,6 +639,22 @@ pub enum Error {
         location: Location,
     },
 
+    #[snafu(display(
+        "Failed to download file, region_id: {}, file_id: {}, file_type: {:?}",
+        region_id,
+        file_id,
+        file_type,
+    ))]
+    Download {
+        region_id: RegionId,
+        file_id: FileId,
+        file_type: FileType,
+        #[snafu(source)]
+        error: std::io::Error,
+        #[snafu(implicit)]
+        location: Location,
+    },
+
     #[snafu(display(
         "Failed to upload file, region_id: {}, file_id: {}, file_type: {:?}",
         region_id,
@@ -965,7 +981,7 @@ impl ErrorExt for Error {
 
             FilterRecordBatch { source, .. } => source.status_code(),
 
-            Upload { .. } => StatusCode::StorageUnavailable,
+            Download { .. } | Upload { .. } => StatusCode::StorageUnavailable,
             ChecksumMismatch { .. } => StatusCode::Unexpected,
             RegionStopped { .. } => StatusCode::RegionNotReady,
             TimeRangePredicateOverflow { .. } => StatusCode::InvalidArguments,

src/mito2/src/metrics.rs

@@ -189,6 +189,17 @@ lazy_static! {
         &[TYPE_LABEL]
     )
     .unwrap();
+    /// Download bytes counter in the write cache.
+    pub static ref WRITE_CACHE_DOWNLOAD_BYTES_TOTAL: IntCounter = register_int_counter!(
+        "mito_write_cache_download_bytes_total",
+        "mito write cache download bytes total",
+    ).unwrap();
+    /// Timer of the downloading task in the write cache.
+    pub static ref WRITE_CACHE_DOWNLOAD_ELAPSED: HistogramVec = register_histogram_vec!(
+        "mito_write_cache_download_elapsed",
+        "mito write cache download elapsed",
+        &[TYPE_LABEL],
+    ).unwrap();
     /// Upload bytes counter.
     pub static ref UPLOAD_BYTES_TOTAL: IntCounter = register_int_counter!(
         "mito_upload_bytes_total",

src/mito2/src/worker.rs

@@ -57,6 +57,7 @@ use crate::request::{
     BackgroundNotify, DdlRequest, SenderDdlRequest, SenderWriteRequest, WorkerRequest,
 };
 use crate::schedule::scheduler::{LocalScheduler, SchedulerRef};
+use crate::sst::file::FileId;
 use crate::sst::index::intermediate::IntermediateManager;
 use crate::sst::index::puffin_manager::PuffinManagerFactory;
 use crate::time_provider::{StdTimeProvider, TimeProviderRef};
@@ -950,6 +951,13 @@ impl WorkerListener {
         // Avoid compiler warning.
         let _ = request_num;
     }
+
+    pub(crate) fn on_file_cache_filled(&self, _file_id: FileId) {
+        #[cfg(any(test, feature = "test"))]
+        if let Some(listener) = &self.listener {
+            listener.on_file_cache_filled(_file_id);
+        }
+    }
 }
 
 #[cfg(test)]

src/mito2/src/worker/handle_manifest.rs

@@ -21,6 +21,8 @@ use std::collections::{HashMap, VecDeque};
 use common_telemetry::{info, warn};
 use store_api::storage::RegionId;
 
+use crate::cache::file_cache::{FileType, IndexKey};
+use crate::cache::CacheManagerRef;
 use crate::error::{RegionBusySnafu, RegionNotFoundSnafu, Result};
 use crate::manifest::action::{
     RegionChange, RegionEdit, RegionMetaAction, RegionMetaActionList, RegionTruncate,
@@ -30,7 +32,8 @@ use crate::request::{
     BackgroundNotify, OptionOutputTx, RegionChangeResult, RegionEditRequest, RegionEditResult,
     TruncateResult, WorkerRequest,
 };
-use crate::worker::RegionWorkerLoop;
+use crate::sst::location;
+use crate::worker::{RegionWorkerLoop, WorkerListener};
 
 pub(crate) type RegionEditQueues = HashMap<RegionId, RegionEditQueue>;
 
@@ -105,10 +108,12 @@ impl<S> RegionWorkerLoop<S> {
         }
 
         let request_sender = self.sender.clone();
+        let cache_manager = self.cache_manager.clone();
+        let listener = self.listener.clone();
         // Now the region is in editing state.
         // Updates manifest in background.
         common_runtime::spawn_global(async move {
-            let result = edit_region(&region, edit.clone()).await;
+            let result = edit_region(&region, edit.clone(), cache_manager, listener).await;
             let notify = WorkerRequest::Background {
                 region_id,
                 notify: BackgroundNotify::RegionEdit(RegionEditResult {
@@ -286,8 +291,40 @@ impl<S> RegionWorkerLoop<S> {
 }
 
 /// Checks the edit, writes and applies it.
-async fn edit_region(region: &MitoRegionRef, edit: RegionEdit) -> Result<()> {
+async fn edit_region(
+    region: &MitoRegionRef,
+    edit: RegionEdit,
+    cache_manager: CacheManagerRef,
+    listener: WorkerListener,
+) -> Result<()> {
     let region_id = region.region_id;
+    if let Some(write_cache) = cache_manager.write_cache() {
+        for file_meta in &edit.files_to_add {
+            let write_cache = write_cache.clone();
+            let layer = region.access_layer.clone();
+            let listener = listener.clone();
+
+            let index_key = IndexKey::new(region_id, file_meta.file_id, FileType::Parquet);
+            let remote_path = location::sst_file_path(layer.region_dir(), file_meta.file_id);
+            common_runtime::spawn_global(async move {
+                if write_cache
+                    .download(index_key, &remote_path, layer.object_store())
+                    .await
+                    .is_ok()
+                {
+                    // Triggers the filling of the parquet metadata cache.
+                    // The parquet file is already downloaded.
+                    let _ = write_cache
+                        .file_cache()
+                        .get_parquet_meta_data(index_key)
+                        .await;
+
+                    listener.on_file_cache_filled(index_key.file_id);
+                }
+            });
+        }
+    }
+
     info!("Applying {edit:?} to region {}", region_id);
 
     let action_list = RegionMetaActionList::with_action(RegionMetaAction::Edit(edit));