ORC-2149: Supports merging multiple ORC files with the same schema into multiple ORC files.

java/tools/src/java/org/apache/orc/tools/Driver.java

@@ -93,7 +93,7 @@ public static void main(String[] args) throws Exception {
       System.err.println("   data - print the data from the ORC file");
       System.err.println("   json-schema - scan JSON files to determine their schema");
       System.err.println("   key - print information about the keys");
-      System.err.println("   merge - merge multiple ORC files into a single ORC file");
+      System.err.println("   merge - merge multiple ORC files into one or more ORC files");
       System.err.println("   meta - print the metadata about the ORC file");
       System.err.println("   scan - scan the ORC file");
       System.err.println("   sizes - list size on disk of each column");

java/tools/src/java/org/apache/orc/tools/MergeFiles.java

@@ -36,10 +36,14 @@
 import java.util.Set;
 
 /**
- * Merge multiple ORC files that all have the same schema into a single ORC file.
+ * Merge multiple ORC files that all have the same schema into one or more ORC files.
+ * When {@code --maxSize} is specified, the tool splits output into multiple part files
+ * under the given output directory, each not exceeding the specified size threshold.
  */
 public class MergeFiles {
 
+  static final String PART_FILE_FORMAT = "part-%05d.orc";
+
   public static void main(Configuration conf, String[] args) throws Exception {
     Options opts = createOptions();
     CommandLine cli = new DefaultParser().parse(opts, args);
@@ -56,27 +60,55 @@ public static void main(Configuration conf, String[] args) throws Exception {
     }
     boolean ignoreExtension = cli.hasOption("ignoreExtension");
 
-    List<Path> inputFiles = new ArrayList<>();
-    OrcFile.WriterOptions writerOptions = OrcFile.writerOptions(conf);
+    long maxSizeBytes = 0;
+    if (cli.hasOption("maxSize")) {
+      maxSizeBytes = Long.parseLong(cli.getOptionValue("maxSize"));
+      if (maxSizeBytes <= 0) {
+        System.err.println("--maxSize must be a positive number of bytes.");
+        System.exit(1);
+      }
+    }
 
+    List<LocatedFileStatus> inputStatuses = new ArrayList<>();
     String[] files = cli.getArgs();
     for (String root : files) {
       Path rootPath = new Path(root);
       FileSystem fs = rootPath.getFileSystem(conf);
       for (RemoteIterator<LocatedFileStatus> itr = fs.listFiles(rootPath, true); itr.hasNext(); ) {
         LocatedFileStatus status = itr.next();
         if (status.isFile() && (ignoreExtension || status.getPath().getName().endsWith(".orc"))) {
-          inputFiles.add(status.getPath());
+          inputStatuses.add(status);
         }
       }
     }
-    if (inputFiles.isEmpty()) {
+    if (inputStatuses.isEmpty()) {
       System.err.println("No files found.");
       System.exit(1);
     }
 
-    List<Path> mergedFiles = OrcFile.mergeFiles(
-        new Path(outputFilename), writerOptions, inputFiles);
+    List<Path> inputFiles = new ArrayList<>(inputStatuses.size());
+    for (LocatedFileStatus s : inputStatuses) {
+      inputFiles.add(s.getPath());
+    }
+
+    OrcFile.WriterOptions writerOptions = OrcFile.writerOptions(conf);
+
+    if (maxSizeBytes > 0) {
+      mergeIntoMultipleFiles(conf, writerOptions, inputStatuses, inputFiles,
+          new Path(outputFilename), maxSizeBytes);
+    } else {
+      mergeIntoSingleFile(writerOptions, inputFiles, new Path(outputFilename), outputFilename);
+    }
+  }
+
+  /**
+   * Original single-output behavior (no --maxSize).
+   */
+  private static void mergeIntoSingleFile(OrcFile.WriterOptions writerOptions,
+                                           List<Path> inputFiles,
+                                           Path outputPath,
+                                           String outputFilename) throws Exception {
+    List<Path> mergedFiles = OrcFile.mergeFiles(outputPath, writerOptions, inputFiles);
 
     List<Path> unSuccessMergedFiles = new ArrayList<>();
     if (mergedFiles.size() != inputFiles.size()) {
@@ -100,11 +132,77 @@ public static void main(Configuration conf, String[] args) throws Exception {
     }
   }
 
+  /**
+   * Multi-output behavior when --maxSize is set.
+   * Input files are grouped by cumulative raw file size; each group is merged into
+   * a separate part file (part-00000.orc, part-00001.orc, ...) under outputDir.
+   * A single file whose size already exceeds maxSizeBytes is placed in its own part.
+   */
+  private static void mergeIntoMultipleFiles(Configuration conf,
+                                              OrcFile.WriterOptions writerOptions,
+                                              List<LocatedFileStatus> inputStatuses,
+                                              List<Path> inputFiles,
+                                              Path outputDir,
+                                              long maxSizeBytes) throws Exception {
+    FileSystem outFs = outputDir.getFileSystem(conf);
+    outFs.mkdirs(outputDir);
+
+    // Group input files into batches where each batch's total size <= maxSizeBytes.
+    List<List<Path>> batches = new ArrayList<>();
+    List<Path> currentBatch = new ArrayList<>();
+    long currentBatchSize = 0;
+
+    for (LocatedFileStatus status : inputStatuses) {
+      long fileSize = status.getLen();
+      if (!currentBatch.isEmpty() && currentBatchSize + fileSize > maxSizeBytes) {
+        batches.add(currentBatch);
+        currentBatch = new ArrayList<>();
+        currentBatchSize = 0;
+      }
+      currentBatch.add(status.getPath());
+      currentBatchSize += fileSize;
+    }
+    if (!currentBatch.isEmpty()) {
+      batches.add(currentBatch);
+    }
+
+    int totalMerged = 0;
+    List<Path> allUnmerged = new ArrayList<>();
+
+    for (int i = 0; i < batches.size(); i++) {
+      List<Path> batch = batches.get(i);
+      Path partOutput = new Path(outputDir, String.format(PART_FILE_FORMAT, i));
+      List<Path> merged = OrcFile.mergeFiles(partOutput, OrcFile.writerOptions(conf), batch);
+      totalMerged += merged.size();
+
+      if (merged.size() != batch.size()) {
+        Set<Path> mergedSet = new HashSet<>(merged);
+        for (Path p : batch) {
+          if (!mergedSet.contains(p)) {
+            allUnmerged.add(p);
+          }
+        }
+      }
+    }
+
+    if (!allUnmerged.isEmpty()) {
+      System.err.println("List of files that could not be merged:");
+      allUnmerged.forEach(path -> System.err.println(path.toString()));
+    }
+
+    System.out.printf(
+        "Output path: %s, Input files size: %d, Merge files size: %d, Output files: %d%n",
+        outputDir, inputFiles.size(), totalMerged, batches.size());
+    if (!allUnmerged.isEmpty()) {
+      System.exit(1);
+    }
+  }
+
   private static Options createOptions() {
     Options result = new Options();
     result.addOption(Option.builder("o")
         .longOpt("output")
-        .desc("Output filename")
+        .desc("Output filename (single-file mode) or output directory (multi-file mode)")
         .hasArg()
         .build());
 
@@ -113,6 +211,15 @@ private static Options createOptions() {
         .desc("Ignore ORC file extension")
         .build());
 
+    result.addOption(Option.builder("m")
+        .longOpt("maxSize")
+        .desc("Maximum size in bytes for each output ORC file. When set, --output is treated as "
+            + "an output directory and merged files are written as part-00000.orc, "
+            + "part-00001.orc, etc. Files are grouped at file boundaries so an individual "
+            + "file larger than this threshold will still be placed in its own part.")
+        .hasArg()
+        .build());
+
     result.addOption(Option.builder("h")
         .longOpt("help")
         .desc("Print help message")

java/tools/src/test/org/apache/orc/tools/TestMergeFiles.java

@@ -53,6 +53,7 @@ public class TestMergeFiles implements TestConf {
   @BeforeEach
   public void openFileSystem() throws Exception {
     fs = FileSystem.getLocal(conf);
+    fs.delete(workDir, true);
     fs.mkdirs(workDir);
     fs.deleteOnExit(workDir);
     testFilePath = new Path(workDir + File.separator + "TestMergeFiles.testMerge.orc");
@@ -107,4 +108,82 @@ public void testMerge() throws Exception {
       assertEquals(10000 + 20000, reader.getNumberOfRows());
     }
   }
+
+  /**
+   * Verifies that --maxSize splits input files into multiple part files under the output
+   * directory. Three source files are created; a tight size threshold forces them to be
+   * written into at least two part files.
+   */
+  @Test
+  public void testMergeWithMaxSize() throws Exception {
+    TypeDescription schema = TypeDescription.fromString("struct<x:int,y:string>");
+
+    // Create 3 source ORC files with different row counts.
+    String[] sourceNames = {
+        workDir + File.separator + "ms-1.orc",
+        workDir + File.separator + "ms-2.orc",
+        workDir + File.separator + "ms-3.orc"
+    };
+    int[] rowCounts = {5000, 5000, 5000};
+    for (int f = 0; f < sourceNames.length; f++) {
+      Writer writer = OrcFile.createWriter(new Path(sourceNames[f]),
+          OrcFile.writerOptions(conf).setSchema(schema));
+      VectorizedRowBatch batch = schema.createRowBatch();
+      LongColumnVector x = (LongColumnVector) batch.cols[0];
+      BytesColumnVector y = (BytesColumnVector) batch.cols[1];
+      for (int r = 0; r < rowCounts[f]; ++r) {
+        int row = batch.size++;
+        x.vector[row] = r;
+        byte[] buffer = ("val-" + r).getBytes();
+        y.setRef(row, buffer, 0, buffer.length);
+        if (batch.size == batch.getMaxSize()) {
+          writer.addRowBatch(batch);
+          batch.reset();
+        }
+      }
+      if (batch.size != 0) {
+        writer.addRowBatch(batch);
+      }
+      writer.close();
+    }
+
+    // Measure the size of the first source file to compute a threshold that forces a split.
+    long singleFileSize = fs.getFileStatus(new Path(sourceNames[0])).getLen();
+    // Threshold: slightly larger than one file so at most one file fits per part.
+    long maxSize = singleFileSize + 1;
+
+    Path outputDir = new Path(workDir + File.separator + "merge-multi-out");
+    fs.delete(outputDir, true);
+
+    PrintStream origOut = System.out;
+    ByteArrayOutputStream myOut = new ByteArrayOutputStream();
+    System.setOut(new PrintStream(myOut, false, StandardCharsets.UTF_8));
+    MergeFiles.main(conf, new String[]{workDir.toString(),
+        "--output", outputDir.toString(),
+        "--maxSize", String.valueOf(maxSize)});
+    System.out.flush();
+    System.setOut(origOut);
+    String output = myOut.toString(StandardCharsets.UTF_8);
+    System.out.println(output);
+
+    assertTrue(output.contains("Input files size: 3"), "Should report 3 input files");
+    assertTrue(output.contains("Merge files size: 3"), "All 3 files should be merged");
+    assertTrue(fs.isDirectory(outputDir), "Output directory should be created");
+
+    // Verify that multiple part files were created and total row count is correct.
+    long totalRows = 0;
+    int partCount = 0;
+    for (int i = 0; ; i++) {
+      Path part = new Path(outputDir, String.format(MergeFiles.PART_FILE_FORMAT, i));
+      if (!fs.exists(part)) {
+        break;
+      }
+      partCount++;
+      try (Reader reader = OrcFile.createReader(part, OrcFile.readerOptions(conf))) {
+        totalRows += reader.getNumberOfRows();
+      }
+    }
+    assertTrue(partCount > 1, "Expected more than one output part file, got: " + partCount);
+    assertEquals(5000 + 5000 + 5000, totalRows, "Total row count across all parts should match");
+  }
 }

site/_docs/java-tools.md

@@ -17,7 +17,7 @@ The subcommands for the tools are:
   * data - print the data of an ORC file
   * json-schema (since ORC 1.4) - determine the schema of JSON documents
   * key (since ORC 1.5) - print information about the encryption keys
-  * merge (since ORC 2.0.1) - merge multiple ORC files into a single ORC file
+  * merge (since ORC 2.0.1) - merge multiple ORC files into one or more ORC files
   * meta - print the metadata of an ORC file
   * scan (since ORC 1.3) - scan the data for benchmarking
   * sizes (since ORC 1.7.2) - list size on disk of each column
@@ -356,13 +356,39 @@ ______________________________________________________________________
 
 ## Java Merge
 
-The merge command can merge multiple ORC files that all have the same schema into a single ORC file.
+The merge command can merge multiple ORC files that all have the same schema. By default
+it writes a single output file. If `--maxSize` is set, `--output` is treated as a directory
+and the tool writes multiple part files (`part-00000.orc`, `part-00001.orc`, …) under it.
+Input files are grouped using their on-disk sizes so that each part’s total input size
+does not exceed the given threshold (a single input file larger than the threshold is still
+merged into its own part).
+
+`-h,--help`
+  : Print help
+
+`-i,--ignoreExtension`
+  : Include files that do not end in `.orc`
+
+`-m,--maxSize <bytes>`
+  : Maximum size in bytes for each output part; enables multi-file output under `--output`
+
+`-o,--output <path>`
+  : Output ORC filename (single-file mode) or output directory (when `--maxSize` is set)
+
+Merge into one ORC file:
 
 ~~~ shell
 % java -jar orc-tools-X.Y.Z-uber.jar merge --output /path/to/merged.orc /path/to/input_orc/
 ______________________________________________________________________
 ~~~
 
+Merge into multiple ORC files under a directory (each part bounded by size):
+
+~~~ shell
+% java -jar orc-tools-X.Y.Z-uber.jar merge --output /path/to/out_dir/ --maxSize 1073741824 /path/to/input_orc/
+______________________________________________________________________
+~~~
+
 ## Java Version
 
 The version command prints the version of this ORC tool.