HDDS-10568. When the ldb command is executed, it is output by line

hadoop-ozone/integration-test/src/test/java/org/apache/hadoop/ozone/debug/TestLDBCli.java

@@ -263,6 +263,66 @@ void testScanOfPipelinesWhenNoData() throws IOException {
     assertEquals("", stderr.toString());
   }
 
+  @Test
+  void testScanWithRecordsPerFile() throws IOException {
+    // Prepare dummy table
+    prepareTable(KEY_TABLE, false);
+
+    String scanDir1 = tempDir.getAbsolutePath() + "/scandir1";
+    // Prepare scan args
+    List<String> completeScanArgs1 = new ArrayList<>(Arrays.asList(
+        "--db", dbStore.getDbLocation().getAbsolutePath(),
+        "scan",
+        "--column-family", KEY_TABLE, "--out", scanDir1 + "/key",
+        "--max-records-per-file", "2"));
+
+    int exitCode1 = cmd.execute(completeScanArgs1.toArray(new String[0]));
+    // Check exit code. Print stderr if not expected
+    assertEquals(0, exitCode1);
+
+    // Number of files generated by traversal
+    int count1 = 0;
+    File tmpDir1 = new File(scanDir1);
+    if (tmpDir1.isDirectory()) {
+      File[] files = tmpDir1.listFiles();
+      if (files != null) {
+        for (File tmpFile : files) {
+          if (tmpFile.isFile() && tmpFile.getName().startsWith("key")) {
+            count1++;
+          }
+        }
+      }
+    }
+
+    assertEquals(count1, 3);
+
+    // Used with parameter '-l'
+    String scanDir2 = tempDir.getAbsolutePath() + "/scandir2";
+    // Prepare scan args
+    List<String> completeScanArgs2 = new ArrayList<>(Arrays.asList(
+        "--db", dbStore.getDbLocation().getAbsolutePath(),
+        "scan",
+        "--column-family", KEY_TABLE, "--out", scanDir2 + "/key",
+        "--max-records-per-file", "3", "-l", "2"));
+
+    int exitCode2 = cmd.execute(completeScanArgs2.toArray(new String[0]));
+    // Check exit code. Print stderr if not expected
+    assertEquals(0, exitCode2);
+    int count2 = 0;
+    File tmpDir2 = new File(scanDir2);
+    if (tmpDir2.isDirectory()) {
+      File[] files = tmpDir2.listFiles();
+      if (files != null) {
+        for (File tmpFile : files) {
+          if (tmpFile.isFile() && tmpFile.getName().startsWith("key")) {
+            count2++;
+          }
+        }
+      }
+    }
+    assertEquals(count2, 2);
+  }
+
   /**
    * Converts String input to a Map and compares to the given Map input.
    * @param expected expected result Map

hadoop-ozone/tools/src/main/java/org/apache/hadoop/ozone/debug/DBScanner.java

@@ -53,6 +53,7 @@
 import picocli.CommandLine;
 
 import java.io.BufferedWriter;
+import java.io.File;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.nio.file.Paths;
@@ -113,6 +114,8 @@ public class DBScanner implements Callable<Void>, SubcommandWithParent {
       description = "File to dump table scan data")
   private String fileName;
 
+  private int fileSuffix = 0;
+
   @CommandLine.Option(names = {"--startkey", "--sk", "-s"},
       description = "Key from which to iterate the DB")
   private String startKey;
@@ -148,6 +151,11 @@ public class DBScanner implements Callable<Void>, SubcommandWithParent {
       defaultValue = "10")
   private int threadCount;
 
+  @CommandLine.Option(names = {"--max-records-per-file"},
+      description = "The number of records to print per file.",
+      defaultValue = "0")
+  private long recordsPerFile;
+
   private static final String KEY_SEPARATOR_SCHEMA_V3 =
       new OzoneConfiguration().getObject(DatanodeConfiguration.class)
           .getContainerSchemaV3KeySeparator();
@@ -217,11 +225,30 @@ private boolean displayTable(ManagedRocksIterator iterator,
       return displayTable(iterator, dbColumnFamilyDef, out(), schemaV3);
     }
 
+    // If there are no parent directories, create them
+    File file = new File(fileName);
+    File parentFile = file.getParentFile();
+    if (!parentFile.exists()) {
+      boolean flg = parentFile.mkdirs();
+      if (!flg) {
+        throw new IOException("An exception occurred while creating " +
+            "the directory. Directorys: " + parentFile.getAbsolutePath());
+      }
+    }
+
     // Write to file output
-    try (PrintWriter out = new PrintWriter(new BufferedWriter(
-        new PrintWriter(fileName, UTF_8.name())))) {
-      return displayTable(iterator, dbColumnFamilyDef, out, schemaV3);
+    while (iterator.get().isValid()) {
+      String fileNameTarget = recordsPerFile > 0 ? fileName + fileSuffix++ :
+          fileName;
+      try (PrintWriter out = new PrintWriter(new BufferedWriter(
+              new PrintWriter(fileNameTarget, UTF_8.name())))) {
+        if (!displayTable(iterator, dbColumnFamilyDef, out, schemaV3)) {
+          return false;
+        }
+      }
     }
+
+    return true;
   }
 
   private boolean displayTable(ManagedRocksIterator iterator,
@@ -288,6 +315,9 @@ private void processRecords(ManagedRocksIterator iterator,
         batch = new ArrayList<>(batchSize);
         sequenceId++;
       }
+      if ((recordsPerFile > 0) && (count >= recordsPerFile)) {
+        break;
+      }
     }
     if (!batch.isEmpty()) {
       Future<Void> future = threadPool.submit(new Task(dbColumnFamilyDef,
@@ -305,7 +335,7 @@ private void processRecords(ManagedRocksIterator iterator,
   }
 
   private boolean withinLimit(long i) {
-    return limit == -1L || i < limit;
+    return recordsPerFile > 0 || limit == -1L || i < limit;
   }
 
   private ColumnFamilyHandle getColumnFamilyHandle(