Support modifying segmentInfos.counter in IndexWriter

lucene/CHANGES.txt

@@ -59,6 +59,8 @@ API Changes
 * GITHUB#14401: Added LeafCollector#collectRange to enable collector to take
   advantage of pre-aggregated data to speed up faceting. (Adrien Grand)
 
+* GITHUB#14417: Support modifying segmentInfos.counter in IndexWriter (Jialiang Guo)
+
 New Features
 ---------------------
 (No changes)

lucene/core/src/java/org/apache/lucene/index/IndexWriter.java

@@ -1427,6 +1427,25 @@ public synchronized void advanceSegmentInfosVersion(long newVersion) {
     changed();
   }
 
+  /**
+   * If {@link SegmentInfos#counter} is below {@code newCounter} then update it to this value.
+   *
+   * @lucene.internal
+   */
+  public synchronized void advanceSegmentInfosCounter(long newCounter) {
+    this.ensureOpen();
+    if (segmentInfos.counter < newCounter) {
+      segmentInfos.counter = newCounter;
+    }
+    changed();
+  }
+
+  /** Returns the {@link SegmentInfos#counter}. */
+  public long getSegmentInfosCounter() {
+    this.ensureOpen();
+    return segmentInfos.counter;
+  }
+
   /**
    * Returns true if this index has deletions (including buffered deletions). Note that this will
    * return true if there are buffered Term/Query deletions, even if it turns out those buffered

lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java

@@ -5037,4 +5037,88 @@ public void testDocValuesSkippingIndexWithoutDocValues() throws Exception {
       }
     }
   }
+
+  public void testAdvanceSegmentInfosCounter() throws IOException {
+    Directory dir = newDirectory();
+    IndexWriter writer;
+    IndexReader reader;
+    writer = new IndexWriter(dir, newIndexWriterConfig(new MockAnalyzer(random())));
+
+    // add 10 documents
+    for (int i = 0; i < 10; i++) {
+      addDocWithIndex(writer, i);
+      writer.commit();
+    }
+    writer.advanceSegmentInfosCounter(1);
+    assertTrue(writer.getSegmentInfosCounter() >= 1);
+
+    writer.advanceSegmentInfosCounter(1000);
+    // add 40 documents
+    for (int i = 10; i < 50; i++) {
+      addDocWithIndex(writer, i);
+      writer.commit();
+    }
+
+    // There may be merge operations in the background, here only verifies that the current segment
+    // counter is greater than 1000.
+    assertTrue(writer.getSegmentInfosCounter() >= 1000);
+
+    IndexWriter.DocStats docStats = writer.getDocStats();
+    assertEquals(50, docStats.maxDoc);
+    assertEquals(50, docStats.numDocs);
+    writer.close();
+
+    // check that the index reader gives the same numbers.
+    reader = DirectoryReader.open(dir);
+    assertEquals(50, reader.maxDoc());
+    assertEquals(50, reader.numDocs());
+    reader.close();
+    dir.close();
+  }
+
+  public void testAdvanceSegmentCounterInCrashAndRecoveryScenario() throws IOException {
+    Directory dir = newDirectory();
+    IndexWriter writer;
+    IndexReader reader;
+    writer = new IndexWriter(dir, newIndexWriterConfig(new MockAnalyzer(random())));
+
+    // add 100 documents
+    for (int i = 0; i < 100; i++) {
+      addDocWithIndex(writer, i);
+      if (random().nextBoolean()) {
+        writer.commit();
+      }
+    }
+    IndexWriter.DocStats docStats = writer.getDocStats();
+    assertEquals(100, docStats.maxDoc);
+    assertEquals(100, docStats.numDocs);
+    writer.commit();
+    writer.close();
+
+    // recovery and advance segment counter
+    writer = new IndexWriter(dir, newIndexWriterConfig(new MockAnalyzer(random())));
+    assertEquals(100, writer.getDocStats().numDocs);
+    long newSegmentCounter = writer.getSegmentInfosCounter() + 1000;
+    writer.advanceSegmentInfosCounter(newSegmentCounter);
+
+    // add 10 documents
+    for (int i = 0; i < 10; i++) {
+      addDocWithIndex(writer, i);
+      if (random().nextBoolean()) {
+        writer.commit();
+      }
+    }
+
+    assertTrue(writer.getSegmentInfosCounter() >= newSegmentCounter);
+
+    assertEquals(110, writer.getDocStats().numDocs);
+    // check that the index reader gives the same numbers.
+    writer.commit();
+    reader = DirectoryReader.open(dir);
+    assertEquals(110, reader.maxDoc());
+    assertEquals(110, reader.numDocs());
+    reader.close();
+    writer.close();
+    dir.close();
+  }
 }

lucene/test-framework/src/java/org/apache/lucene/tests/index/ThreadedIndexingAndSearchingTestCase.java

@@ -82,6 +82,7 @@ public abstract class ThreadedIndexingAndSearchingTestCase extends LuceneTestCas
   protected final AtomicInteger addCount = new AtomicInteger();
   protected final AtomicInteger delCount = new AtomicInteger();
   protected final AtomicInteger packCount = new AtomicInteger();
+  protected AtomicLong maxAdvancedSegmentCounter = new AtomicLong(0);
 
   protected Directory dir;
   protected IndexWriter writer;
@@ -189,6 +190,20 @@ public void run() {
                     addedField = null;
                   }
 
+                  // Maybe advance segment counter. Run with a relatively low probability to avoid
+                  // testing slowdowns caused by synchronous operations.
+                  if (random().nextInt(7) == 5) {
+                    long newSegmentCounter = writer.getSegmentInfosCounter() + 100;
+                    writer.advanceSegmentInfosCounter(newSegmentCounter);
+                    if (VERBOSE) {
+                      System.out.println(
+                          Thread.currentThread().getName()
+                              + " advance segment counter to "
+                              + newSegmentCounter);
+                    }
+                    maxAdvancedSegmentCounter.accumulateAndGet(newSegmentCounter, Math::max);
+                  }
+
                   if (random().nextBoolean()) {
 
                     if (random().nextBoolean()) {
@@ -606,14 +621,18 @@ public void message(String component, String message) {
       thread.join();
     }
 
+    assertTrue(writer.getSegmentInfosCounter() >= maxAdvancedSegmentCounter.get());
+
     if (VERBOSE) {
       System.out.println(
           "TEST: done join indexing threads ["
               + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - t0)
               + " ms]; addCount="
               + addCount
               + " delCount="
-              + delCount);
+              + delCount
+              + " segmentCounter="
+              + writer.getSegmentInfosCounter());
     }
 
     final IndexSearcher s = getFinalSearcher();