Fix CCR compatibility with remote translogs

src/main/kotlin/org/opensearch/replication/ReplicationPlugin.kt

@@ -144,12 +144,14 @@
 import java.util.function.Supplier
 
 import org.opensearch.index.engine.NRTReplicationEngine
+import org.opensearch.replication.util.ValidationUtil
 
 
 @OpenForTesting
 internal class ReplicationPlugin : Plugin(), ActionPlugin, PersistentTaskPlugin, RepositoryPlugin, EnginePlugin {
 
     private lateinit var client: Client
+    private lateinit var clusterService: ClusterService
     private lateinit var threadPool: ThreadPool
     private lateinit var replicationMetadataManager: ReplicationMetadataManager
     private lateinit var replicationSettings: ReplicationSettings
@@ -207,6 +209,7 @@
                                   repositoriesService: Supplier<RepositoriesService>): Collection<Any> {
         this.client = client
         this.threadPool = threadPool
+        this.clusterService = clusterService
         this.replicationMetadataManager = ReplicationMetadataManager(clusterService, client,
                 ReplicationMetadataStore(client, clusterService, xContentRegistry))
         this.replicationSettings = ReplicationSettings(clusterService)
@@ -379,9 +382,15 @@
     }
 
     override fun getCustomTranslogDeletionPolicyFactory(): Optional<TranslogDeletionPolicyFactory> {
-       return Optional.of(TranslogDeletionPolicyFactory{
-               indexSettings, retentionLeasesSupplier -> ReplicationTranslogDeletionPolicy(indexSettings, retentionLeasesSupplier)
-       })
+        // We don't need a retention lease translog deletion policy for remote store enabled clusters as
+        // we fetch the operations directly from lucene in such cases.
+        return if (ValidationUtil.isRemoteStoreEnabledCluster(clusterService) == false) {
+            Optional.of(TranslogDeletionPolicyFactory { indexSettings, retentionLeasesSupplier ->
+                ReplicationTranslogDeletionPolicy(indexSettings, retentionLeasesSupplier)
+            })
+        } else {
+            Optional.empty()
+        }
     }
 
     override fun onIndexModule(indexModule: IndexModule) {

src/main/kotlin/org/opensearch/replication/action/changes/TransportGetChangesAction.kt

@@ -27,17 +27,15 @@
 import org.opensearch.core.common.io.stream.Writeable
 import org.opensearch.common.unit.TimeValue
 import org.opensearch.core.index.shard.ShardId
+import org.opensearch.index.shard.IndexShard
 import org.opensearch.index.translog.Translog
 import org.opensearch.indices.IndicesService
 import org.opensearch.replication.ReplicationPlugin.Companion.REPLICATION_INDEX_TRANSLOG_PRUNING_ENABLED_SETTING
 import org.opensearch.replication.ReplicationPlugin.Companion.REPLICATION_EXECUTOR_NAME_LEADER
 import org.opensearch.replication.seqno.RemoteClusterStats
 import org.opensearch.replication.seqno.RemoteClusterTranslogService
 import org.opensearch.replication.seqno.RemoteShardMetric
-import org.opensearch.replication.util.completeWith
-import org.opensearch.replication.util.coroutineContext
-import org.opensearch.replication.util.stackTraceToString
-import org.opensearch.replication.util.waitForGlobalCheckpoint
+import org.opensearch.replication.util.*
 import org.opensearch.threadpool.ThreadPool
 import org.opensearch.transport.TransportActionProxy
 import org.opensearch.transport.TransportService
@@ -79,7 +77,8 @@
                 indexMetric.lastFetchTime.set(relativeStartNanos)
 
                 val indexShard = indicesService.indexServiceSafe(shardId.index).getShard(shardId.id)
-                if (indexShard.lastSyncedGlobalCheckpoint < request.fromSeqNo) {
+                val isRemoteStoreEnabled = ValidationUtil.isRemoteStoreEnabledCluster(clusterService)
+                if (lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled) < request.fromSeqNo) {
                     // There are no new operations to sync. Do a long poll and wait for GlobalCheckpoint to advance. If
                     // the checkpoint doesn't advance by the timeout this throws an ESTimeoutException which the caller
                     // should catch and start a new poll.
@@ -88,18 +87,18 @@
                     // At this point indexShard.lastKnownGlobalCheckpoint  has advanced but it may not yet have been synced
                     // to the translog, which means we can't return those changes. Return to the caller to retry.
                     // TODO: Figure out a better way to wait for the global checkpoint to be synced to the translog
-                    if (indexShard.lastSyncedGlobalCheckpoint < request.fromSeqNo) {
-                        assert(gcp > indexShard.lastSyncedGlobalCheckpoint) { "Checkpoint didn't advance at all" }
+                    if (lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled) < request.fromSeqNo) {
+                        assert(gcp > lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled)) { "Checkpoint didn't advance at all $gcp ${lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled)}" }
                         throw OpenSearchTimeoutException("global checkpoint not synced. Retry after a few miliseconds...")
                     }
                 }
 
                 relativeStartNanos  = System.nanoTime()
                 // At this point lastSyncedGlobalCheckpoint is at least fromSeqNo
-                val toSeqNo = min(indexShard.lastSyncedGlobalCheckpoint, request.toSeqNo)
+                val toSeqNo = min(lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled), request.toSeqNo)
 
                 var ops: List<Translog.Operation> = listOf()
-                var fetchFromTranslog = isTranslogPruningByRetentionLeaseEnabled(shardId)
+                var fetchFromTranslog = isTranslogPruningByRetentionLeaseEnabled(shardId) && isRemoteStoreEnabled == false
                 if(fetchFromTranslog) {
                     try {
                         ops = translogService.getHistoryOfOperations(indexShard, request.fromSeqNo, toSeqNo)
@@ -137,12 +136,22 @@
                 indexMetric.ops.addAndGet(ops.size.toLong())
 
                 ops.stream().forEach{op -> indexMetric.bytesRead.addAndGet(op.estimateSize()) }
-
-                GetChangesResponse(ops, request.fromSeqNo, indexShard.maxSeqNoOfUpdatesOrDeletes, indexShard.lastSyncedGlobalCheckpoint)
+                GetChangesResponse(ops, request.fromSeqNo, indexShard.maxSeqNoOfUpdatesOrDeletes, lastGlobalCheckpoint(indexShard, isRemoteStoreEnabled))
             }
         }
     }
 
+    private fun lastGlobalCheckpoint(indexShard: IndexShard, isRemoteStoreEnabled: Boolean): Long {
+        // We rely on lastSyncedGlobalCheckpoint as it has been durably written to disk. In case of remote store
+        // enabled clusters, the semantics are slightly different, and we can't use lastSyncedGlobalCheckpoint. Falling back to
+        // lastKnownGlobalCheckpoint in such cases.
+        return if (isRemoteStoreEnabled) {
+            indexShard.lastKnownGlobalCheckpoint
+        } else {
+            indexShard.lastSyncedGlobalCheckpoint
+        }
+    }
+
 
     private fun isTranslogPruningByRetentionLeaseEnabled(shardId: ShardId): Boolean {
         val enabled = clusterService.state().metadata.indices.get(shardId.indexName)
@@ -162,7 +171,9 @@
     }
 
     override fun shards(state: ClusterState, request: InternalRequest): ShardsIterator {
+        val shardIt = state.routingTable().shardRoutingTable(request.request().shardId)
         // Random active shards
-        return state.routingTable().shardRoutingTable(request.request().shardId).activeInitializingShardsRandomIt()
+        return if (ValidationUtil.isRemoteStoreEnabledCluster(clusterService)) shardIt.primaryShardIt()
+        else shardIt.activeInitializingShardsRandomIt()
     }
 }

src/main/kotlin/org/opensearch/replication/repository/RemoteClusterRepository.kt

@@ -245,6 +245,9 @@ class RemoteClusterRepository(private val repositoryMetadata: RepositoryMetadata
 
         // Remove translog pruning for the follower index
         builder.remove(REPLICATION_INDEX_TRANSLOG_PRUNING_ENABLED_SETTING.key)
+        builder.remove(IndexMetadata.SETTING_REMOTE_STORE_ENABLED)
+        builder.remove(IndexMetadata.SETTING_REMOTE_SEGMENT_STORE_REPOSITORY)
+        builder.remove(IndexMetadata.SETTING_REMOTE_TRANSLOG_STORE_REPOSITORY)
 
         val indexMdBuilder = IndexMetadata.builder(indexMetadata).settings(builder)
         indexMetadata.aliases.values.forEach {

src/main/kotlin/org/opensearch/replication/util/ValidationUtil.kt

@@ -24,8 +24,11 @@ import org.opensearch.env.Environment
 import org.opensearch.index.IndexNotFoundException
 import java.io.UnsupportedEncodingException
 import org.opensearch.cluster.service.ClusterService
+import org.opensearch.node.Node
+import org.opensearch.node.remotestore.RemoteStoreNodeAttribute
 import org.opensearch.replication.ReplicationPlugin.Companion.KNN_INDEX_SETTING
 import org.opensearch.replication.ReplicationPlugin.Companion.KNN_PLUGIN_PRESENT_SETTING
+import org.opensearch.replication.action.changes.TransportGetChangesAction
 import java.nio.file.Files
 import java.nio.file.Path
 import java.util.Locale
@@ -154,4 +157,8 @@ object ValidationUtil {
 
     }
 
+    fun isRemoteStoreEnabledCluster(clusterService: ClusterService): Boolean {
+        return clusterService.settings.getByPrefix(Node.NODE_ATTRIBUTES.key + RemoteStoreNodeAttribute.REMOTE_STORE_NODE_ATTRIBUTE_KEY_PREFIX).isEmpty == false
+    }
+
 }