HBASE-27644 Should not return false when WALKey has no following KVs while reading WAL file (#5032)

Signed-off-by: Viraj Jasani <vjasani@apache.org>
(cherry picked from commit 4a9cf99b2f)

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/ProtobufLogReader.java

@@ -408,10 +408,9 @@ public class ProtobufLogReader extends ReaderBase {
       WALKey walKey = builder.build();
       entry.getKey().readFieldsFromPb(walKey, this.byteStringUncompressor);
       if (!walKey.hasFollowingKvCount() || 0 == walKey.getFollowingKvCount()) {
-        LOG.trace("WALKey has no KVs that follow it; trying the next one. current offset={}",
+        LOG.debug("WALKey has no KVs that follow it; trying the next one. current offset={}",
           this.inputStream.getPos());
-        seekOnFs(originalPosition);
+        return true;
-        return false;
       }
       int expectedCells = walKey.getFollowingKvCount();
       long posBefore = this.inputStream.getPos();

hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALSplit.java

@@ -276,7 +276,7 @@ public class TestWALSplit {
    * log entry. Does its writing as an alternate user in another filesystem instance to simulate
    * better it being a regionserver.
    */
-  class ZombieLastLogWriterRegionServer extends Thread {
+  private class ZombieLastLogWriterRegionServer extends Thread {
     final AtomicLong editsCount;
     final AtomicBoolean stop;
     final int numOfWriters;
@@ -402,10 +402,6 @@ public class TestWALSplit {
 
   private Path createRecoveredEditsPathForRegion() throws IOException {
     byte[] encoded = RegionInfoBuilder.FIRST_META_REGIONINFO.getEncodedNameAsBytes();
-    long now = EnvironmentEdgeManager.currentTime();
-    Entry entry = new Entry(
-      new WALKeyImpl(encoded, TableName.META_TABLE_NAME, 1, now, HConstants.DEFAULT_CLUSTER_ID),
-      new WALEdit());
     Path p = WALSplitUtil.getRegionSplitEditsPath(TableName.META_TABLE_NAME, encoded, 1,
       FILENAME_BEING_SPLIT, TMPDIRNAME, conf);
     return p;
@@ -491,10 +487,10 @@ public class TestWALSplit {
     assertEquals(11, countWAL(splitLog[0]));
   }
 
-  /*
+  /**
    * Tests that WalSplitter ignores replication marker edits.
    */
-  @Test(timeout = 30000)
+  @Test
   public void testSplitRemovesReplicationMarkerEdits() throws IOException {
     RegionInfo regionInfo = ReplicationMarkerChore.REGION_INFO;
     Path path = new Path(WALDIR, WAL_FILE_PREFIX + "1");
@@ -1206,7 +1202,44 @@ public class TestWALSplit {
     } finally {
       conf.unset(HConstants.WAL_STORAGE_POLICY);
     }
+  }
 
+  /**
+   * See HBASE-27644, typically we should not have empty WALEdit but we should be able to process
+   * it, instead of losing data after it.
+   */
+  @Test
+  public void testEmptyWALEdit() throws IOException {
+    final String region = "region__5";
+    REGIONS.clear();
+    REGIONS.add(region);
+    makeRegionDirs(REGIONS);
+    fs.mkdirs(WALDIR);
+    Path path = new Path(WALDIR, WAL_FILE_PREFIX + 5);
+    generateEmptyEditWAL(path, Bytes.toBytes(region));
+    useDifferentDFSClient();
+
+    Path regiondir = new Path(TABLEDIR, region);
+    fs.mkdirs(regiondir);
+    List<Path> splitPaths = WALSplitter.split(HBASELOGDIR, WALDIR, OLDLOGDIR, fs, conf, wals);
+    // Make sure that WALSplitter generate the split file
+    assertEquals(1, splitPaths.size());
+
+    Path originalLog = (fs.listStatus(OLDLOGDIR))[0].getPath();
+    assertEquals(11, countWAL(originalLog));
+    // we will skip the empty WAL when splitting
+    assertEquals(10, countWAL(splitPaths.get(0)));
+  }
+
+  private void generateEmptyEditWAL(Path path, byte[] region) throws IOException {
+    fs.mkdirs(WALDIR);
+    try (Writer writer = wals.createWALWriter(fs, path)) {
+      long seq = 0;
+      appendEmptyEntry(writer, TABLE_NAME, region, seq++);
+      for (int i = 0; i < 10; i++) {
+        appendEntry(writer, TABLE_NAME, region, Bytes.toBytes(i), FAMILY, QUALIFIER, VALUE, seq++);
+      }
+    }
   }
 
   private Writer generateWALs(int leaveOpen) throws IOException {
@@ -1399,7 +1432,7 @@ public class TestWALSplit {
     w.sync(false);
   }
 
-  public static long appendEntry(Writer writer, TableName table, byte[] region, byte[] row,
+  private static long appendEntry(Writer writer, TableName table, byte[] region, byte[] row,
     byte[] family, byte[] qualifier, byte[] value, long seq) throws IOException {
     LOG.info(Thread.currentThread().getName() + " append");
     writer.append(createTestEntry(table, region, row, family, qualifier, value, seq));
@@ -1412,13 +1445,27 @@ public class TestWALSplit {
     byte[] qualifier, byte[] value, long seq) {
     long time = System.nanoTime();
 
-    seq++;
     final KeyValue cell = new KeyValue(row, family, qualifier, time, KeyValue.Type.Put, value);
     WALEdit edit = new WALEdit();
     edit.add(cell);
     return new Entry(new WALKeyImpl(region, table, seq, time, HConstants.DEFAULT_CLUSTER_ID), edit);
   }
 
+  private static long appendEmptyEntry(Writer writer, TableName table, byte[] region, long seq)
+    throws IOException {
+    LOG.info(Thread.currentThread().getName() + " append");
+    writer.append(createEmptyEntry(table, region, seq));
+    LOG.info(Thread.currentThread().getName() + " sync");
+    writer.sync(false);
+    return seq;
+  }
+
+  private static Entry createEmptyEntry(TableName table, byte[] region, long seq) {
+    long time = System.nanoTime();
+    return new Entry(new WALKeyImpl(region, table, seq, time, HConstants.DEFAULT_CLUSTER_ID),
+      new WALEdit());
+  }
+
   private void injectEmptyFile(String suffix, boolean closeFile) throws IOException {
     Writer writer =
       WALFactory.createWALWriter(fs, new Path(WALDIR, WAL_FILE_PREFIX + suffix), conf);
@@ -1428,9 +1475,7 @@ public class TestWALSplit {
   }
 
   private boolean logsAreEqual(Path p1, Path p2) throws IOException {
-    Reader in1, in2;
+    try (Reader in1 = wals.createReader(fs, p1); Reader in2 = wals.createReader(fs, p2)) {
-    in1 = wals.createReader(fs, p1);
-    in2 = wals.createReader(fs, p2);
       Entry entry1;
       Entry entry2;
       while ((entry1 = in1.next()) != null) {
@@ -1442,8 +1487,7 @@ public class TestWALSplit {
           return false;
         }
       }
-    in1.close();
+    }
-    in2.close();
     return true;
   }
 }