Fix SegRep bug where primary shards do not update tracked replica sta…

…te post failover/relocation (opensearch-project#11017) (opensearch-project#11018)

(cherry picked from commit a2febe9)

Signed-off-by: Marc Handalian <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

server/src/internalClusterTest/java/org/opensearch/indices/replication/SegmentReplicationIT.java

@@ -22,6 +22,7 @@
 import org.apache.lucene.index.StandardDirectoryReader;
 import org.apache.lucene.tests.util.TestUtil;
 import org.apache.lucene.util.BytesRef;
+import org.opensearch.action.admin.cluster.stats.ClusterStatsResponse;
 import org.opensearch.action.admin.indices.alias.Alias;
 import org.opensearch.action.admin.indices.flush.FlushRequest;
 import org.opensearch.action.admin.indices.stats.IndicesStatsRequest;
@@ -62,6 +63,7 @@
 import org.opensearch.core.index.shard.ShardId;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.index.IndexModule;
+import org.opensearch.index.ReplicationStats;
 import org.opensearch.index.SegmentReplicationPerGroupStats;
 import org.opensearch.index.SegmentReplicationPressureService;
 import org.opensearch.index.SegmentReplicationShardStats;
@@ -94,6 +96,7 @@
 import java.util.Set;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
 import static java.util.Arrays.asList;
@@ -1776,4 +1779,58 @@ public void testRealtimeTermVectorRequestsUnSuccessful() throws IOException {
         assertThat(response.getIndex(), equalTo(INDEX_NAME));
 
     }
+
+    public void testReplicaAlreadyAtCheckpoint() throws Exception {
+        final List<String> nodes = new ArrayList<>();
+        final String primaryNode = internalCluster().startDataOnlyNode();
+        nodes.add(primaryNode);
+        final Settings settings = Settings.builder().put(indexSettings()).put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0).build();
+        createIndex(INDEX_NAME, settings);
+        ensureGreen(INDEX_NAME);
+        // start a replica node, initially will be empty with no shard assignment.
+        final String replicaNode = internalCluster().startDataOnlyNode();
+        nodes.add(replicaNode);
+        final String replicaNode2 = internalCluster().startDataOnlyNode();
+        assertAcked(
+            client().admin()
+                .indices()
+                .prepareUpdateSettings(INDEX_NAME)
+                .setSettings(Settings.builder().put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 2))
+        );
+        ensureGreen(INDEX_NAME);
+
+        // index a doc.
+        client().prepareIndex(INDEX_NAME).setId("1").setSource("foo", randomInt()).get();
+        refresh(INDEX_NAME);
+
+        internalCluster().stopRandomNode(InternalTestCluster.nameFilter(primaryNode));
+        ensureYellowAndNoInitializingShards(INDEX_NAME);
+        IndexShard replica_1 = getIndexShard(replicaNode, INDEX_NAME);
+        IndexShard replica_2 = getIndexShard(replicaNode2, INDEX_NAME);
+        // wait until a replica is promoted & finishes engine flip, we don't care which one
+        AtomicReference<IndexShard> primary = new AtomicReference<>();
+        assertBusy(() -> {
+            assertTrue("replica should be promoted as a primary", replica_1.routingEntry().primary() || replica_2.routingEntry().primary());
+            primary.set(replica_1.routingEntry().primary() ? replica_1 : replica_2);
+        });
+
+        FlushRequest request = new FlushRequest(INDEX_NAME);
+        request.force(true);
+        primary.get().flush(request);
+
+        assertBusy(() -> {
+            assertEquals(
+                replica_1.getLatestReplicationCheckpoint().getSegmentInfosVersion(),
+                replica_2.getLatestReplicationCheckpoint().getSegmentInfosVersion()
+            );
+        });
+
+        assertBusy(() -> {
+            ClusterStatsResponse clusterStatsResponse = client().admin().cluster().prepareClusterStats().get();
+            ReplicationStats replicationStats = clusterStatsResponse.getIndicesStats().getSegments().getReplicationStats();
+            assertEquals(0L, replicationStats.maxBytesBehind);
+            assertEquals(0L, replicationStats.maxReplicationLag);
+            assertEquals(0L, replicationStats.totalBytesBehind);
+        });
+    }
 }

server/src/main/java/org/opensearch/indices/replication/SegmentReplicationTargetService.java

@@ -53,6 +53,7 @@
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicLong;
 
+import static org.opensearch.index.seqno.SequenceNumbers.NO_OPS_PERFORMED;
 import static org.opensearch.indices.replication.SegmentReplicationSourceService.Actions.UPDATE_VISIBLE_CHECKPOINT;
 
 /**
@@ -282,6 +283,12 @@ public void onReplicationFailure(
                         }
                     }
                 });
+            } else if (replicaShard.isSegmentReplicationAllowed()) {
+                // if we didn't process the checkpoint because we are up to date,
+                // send our latest checkpoint to the primary to update tracking.
+                // replicationId is not used by the primary set to a default value.
+                final long replicationId = NO_OPS_PERFORMED;
+                updateVisibleCheckpoint(replicationId, replicaShard);
             }
         } else {
             logger.trace(

server/src/test/java/org/opensearch/indices/replication/SegmentReplicationTargetServiceTests.java

@@ -54,7 +54,7 @@
 import java.util.concurrent.TimeUnit;
 import java.util.function.BiConsumer;
 
-import static org.junit.Assert.assertEquals;
+import static org.opensearch.index.seqno.SequenceNumbers.NO_OPS_PERFORMED;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyLong;
 import static org.mockito.Mockito.atLeastOnce;
@@ -250,6 +250,7 @@ public void testAlreadyOnNewCheckpoint() {
         SegmentReplicationTargetService spy = spy(sut);
         spy.onNewCheckpoint(replicaShard.getLatestReplicationCheckpoint(), replicaShard);
         verify(spy, times(0)).startReplication(any(), any(), any());
+        verify(spy, times(1)).updateVisibleCheckpoint(NO_OPS_PERFORMED, replicaShard);
     }
 
     @AwaitsFix(bugUrl = "https://github.com/opensearch-project/OpenSearch/issues/8928")