feat: flush other workers if still need flush (#4746)

src/mito2/src/engine/flush_test.rs

@@ -402,3 +402,72 @@ async fn test_auto_flush_engine() {
 +-------+---------+---------------------+";
     assert_eq!(expected, batches.pretty_print().unwrap());
 }
+
+#[tokio::test]
+async fn test_flush_workers() {
+    let mut env = TestEnv::new();
+    let write_buffer_manager = Arc::new(MockWriteBufferManager::default());
+    let listener = Arc::new(FlushListener::default());
+    let engine = env
+        .create_engine_with(
+            MitoConfig {
+                num_workers: 2,
+                ..Default::default()
+            },
+            Some(write_buffer_manager.clone()),
+            Some(listener.clone()),
+        )
+        .await;
+
+    let region_id0 = RegionId::new(1, 0);
+    let region_id1 = RegionId::new(1, 1);
+    let request = CreateRequestBuilder::new().region_dir("r0").build();
+    let column_schemas = rows_schema(&request);
+    engine
+        .handle_request(region_id0, RegionRequest::Create(request))
+        .await
+        .unwrap();
+    let request = CreateRequestBuilder::new().region_dir("r1").build();
+    engine
+        .handle_request(region_id1, RegionRequest::Create(request.clone()))
+        .await
+        .unwrap();
+
+    // Prepares rows for flush.
+    let rows = Rows {
+        schema: column_schemas.clone(),
+        rows: build_rows_for_key("a", 0, 2, 0),
+    };
+    put_rows(&engine, region_id0, rows.clone()).await;
+    put_rows(&engine, region_id1, rows).await;
+
+    write_buffer_manager.set_should_flush(true);
+
+    // Writes to the mutable memtable and triggers flush for region 0.
+    let rows = Rows {
+        schema: column_schemas.clone(),
+        rows: build_rows_for_key("b", 0, 2, 0),
+    };
+    put_rows(&engine, region_id0, rows).await;
+
+    // Waits until flush is finished.
+    while listener.success_count() < 2 {
+        listener.wait().await;
+    }
+
+    // Scans region 1.
+    let request = ScanRequest::default();
+    let scanner = engine.scanner(region_id1, request).unwrap();
+    assert_eq!(0, scanner.num_memtables());
+    assert_eq!(1, scanner.num_files());
+    let stream = scanner.scan().await.unwrap();
+    let batches = RecordBatches::try_collect(stream).await.unwrap();
+    let expected = "\
++-------+---------+---------------------+
+| tag_0 | field_0 | ts                  |
++-------+---------+---------------------+
+| a     | 0.0     | 1970-01-01T00:00:00 |
+| a     | 1.0     | 1970-01-01T00:00:01 |
++-------+---------+---------------------+";
+    assert_eq!(expected, batches.pretty_print().unwrap());
+}

src/mito2/src/engine/listener.rs

@@ -14,6 +14,7 @@
 
 //! Engine event listener for tests.
 
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -77,21 +78,28 @@ pub type EventListenerRef = Arc<dyn EventListener>;
 #[derive(Default)]
 pub struct FlushListener {
     notify: Notify,
+    success_count: AtomicUsize,
 }
 
 impl FlushListener {
     /// Wait until one flush job is done.
     pub async fn wait(&self) {
         self.notify.notified().await;
     }
+
+    /// Returns the success count.
+    pub fn success_count(&self) -> usize {
+        self.success_count.load(Ordering::Relaxed)
+    }
 }
 
 #[async_trait]
 impl EventListener for FlushListener {
     fn on_flush_success(&self, region_id: RegionId) {
         info!("Region {} flush successfully", region_id);
 
-        self.notify.notify_one()
+        self.success_count.fetch_add(1, Ordering::Relaxed);
+        self.notify.notify_one();
     }
 }
 

src/mito2/src/worker.rs

@@ -670,6 +670,11 @@ impl<S: LogStore> RegionWorkerLoop<S> {
                         // The channel is disconnected.
                         break;
                     } else {
+                        // Also flush this worker if other workers trigger flush as this worker may have
+                        // a large memtable to flush. We may not have chance to flush that memtable if we
+                        // never write to this worker. So only flushing other workers may not release enough
+                        // memory.
+                        self.maybe_flush_worker();
                         // A flush job is finished, handles stalled requests.
                         self.handle_stalled_requests().await;
                         continue;