[IOTDB-2723] Fix sequence inner space compaction lose data

server/src/main/java/org/apache/iotdb/db/engine/compaction/inner/utils/SingleSeriesCompactionExecutor.java

@@ -209,7 +209,14 @@ private void writeChunkIntoChunkWriter(Chunk chunk) throws IOException {
   }
 
   private void writeCachedChunkIntoChunkWriter() throws IOException {
-    cachedChunk.getData().flip();
+    if (cachedChunk.getData().position() != 0) {
+      // If the position of cache chunk data buffer is 0,
+      // it means that the cache chunk is the first chunk cached,
+      // and it hasn't merged with any chunk yet.
+      // If we flip it, both the position and limit in the buffer will be 0,
+      // which leads to the lost of data.
+      cachedChunk.getData().flip();
+    }
     writeChunkIntoChunkWriter(cachedChunk);
     cachedChunk = null;
     cachedChunkMetadata = null;

server/src/test/java/org/apache/iotdb/db/engine/compaction/inner/InnerSpaceCompactionUtilsNoAlignedTest.java

@@ -758,7 +758,7 @@ public void testDeserializeCachedChunk() throws Exception {
   }
 
   @Test
-  public void testMixCompact() throws Exception {
+  public void testMixCompact1() throws Exception {
     long testTargetChunkPointNum = 2000L;
     long testChunkSizeLowerBound = 1024L;
     long testChunkPointNumLowerBound = 100L;
@@ -834,4 +834,85 @@ public void testMixCompact() throws Exception {
           .setChunkPointNumLowerBoundInCompaction(originChunkPointNumLowerBound);
     }
   }
+
+  @Test
+  public void testMixCompact2() throws Exception {
+    long testTargetChunkPointNum = 2000L;
+    long testChunkSizeLowerBound = 1024L;
+    long testChunkPointNumLowerBound = 100L;
+    long originTargetChunkSize = IoTDBDescriptor.getInstance().getConfig().getTargetChunkSize();
+    long originTargetChunkPointNum =
+        IoTDBDescriptor.getInstance().getConfig().getTargetChunkPointNum();
+    IoTDBDescriptor.getInstance().getConfig().setTargetChunkSize(1024 * 1024);
+    IoTDBDescriptor.getInstance().getConfig().setTargetChunkPointNum(testTargetChunkPointNum);
+    long originChunkSizeLowerBound =
+        IoTDBDescriptor.getInstance().getConfig().getChunkSizeLowerBoundInCompaction();
+    IoTDBDescriptor.getInstance()
+        .getConfig()
+        .setChunkSizeLowerBoundInCompaction(testChunkSizeLowerBound);
+    long originChunkPointNumLowerBound =
+        IoTDBDescriptor.getInstance().getConfig().getChunkPointNumLowerBoundInCompaction();
+    IoTDBDescriptor.getInstance()
+        .getConfig()
+        .setChunkPointNumLowerBoundInCompaction(testChunkPointNumLowerBound);
+    try {
+      List<TsFileResource> sourceFiles = new ArrayList();
+      int fileNum = 12;
+      long pointStep = 10L;
+      long[] points = new long[] {1960, 50, 1960, 50, 2100, 50, 1960, 2300, 2500, 1000, 500, 500};
+      for (int i = 0; i < fileNum; ++i) {
+        List<List<Long>> chunkPagePointsNum = new ArrayList<>();
+        List<Long> pagePointsNum = new ArrayList<>();
+        pagePointsNum.add(points[i]);
+        chunkPagePointsNum.add(pagePointsNum);
+        TsFileResource resource =
+            new TsFileResource(new File(SEQ_DIRS, String.format("%d-%d-0-0.tsfile", i + 1, i + 1)));
+        sourceFiles.add(resource);
+        CompactionFileGeneratorUtils.writeTsFile(
+            fullPathSet, chunkPagePointsNum, i * 2500L, resource);
+      }
+
+      Map<PartialPath, List<TimeValuePair>> originData =
+          CompactionCheckerUtils.getDataByQuery(paths, schemaList, sourceFiles, new ArrayList<>());
+      TsFileNameGenerator.TsFileName tsFileName =
+          TsFileNameGenerator.getTsFileName(sourceFiles.get(0).getTsFile().getName());
+      TsFileResource targetResource =
+          new TsFileResource(
+              new File(
+                  SEQ_DIRS,
+                  String.format(
+                      "%d-%d-%d-%d.tsfile",
+                      tsFileName.getTime(),
+                      tsFileName.getVersion(),
+                      tsFileName.getInnerCompactionCnt() + 1,
+                      tsFileName.getCrossCompactionCnt())));
+      InnerSpaceCompactionUtils.compact(targetResource, sourceFiles);
+      Map<String, List<List<Long>>> chunkPagePointsNumMerged = new HashMap<>();
+      // outer list is a chunk, inner list is point num in each page
+      for (String path : fullPathSet) {
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2010);
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2010);
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2100);
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2010);
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2300);
+        CompactionCheckerUtils.putOnePageChunk(chunkPagePointsNumMerged, path, 2500);
+        CompactionCheckerUtils.putChunk(
+            chunkPagePointsNumMerged, path, new long[] {1000, 500, 500});
+      }
+      Map<PartialPath, List<TimeValuePair>> compactedData =
+          CompactionCheckerUtils.getDataByQuery(
+              paths, schemaList, Collections.singletonList(targetResource), new ArrayList<>());
+      CompactionCheckerUtils.validDataByValueList(originData, compactedData);
+      CompactionCheckerUtils.checkChunkAndPage(chunkPagePointsNumMerged, targetResource);
+    } finally {
+      IoTDBDescriptor.getInstance().getConfig().setTargetChunkSize(originTargetChunkSize);
+      IoTDBDescriptor.getInstance().getConfig().setTargetChunkPointNum(originTargetChunkPointNum);
+      IoTDBDescriptor.getInstance()
+          .getConfig()
+          .setChunkSizeLowerBoundInCompaction(originChunkSizeLowerBound);
+      IoTDBDescriptor.getInstance()
+          .getConfig()
+          .setChunkPointNumLowerBoundInCompaction(originChunkPointNumLowerBound);
+    }
+  }
 }