Disallow multiple concurrent recovery attempts for same target shard (#25428)

The primary shard uses the GlobalCheckPointTracker to track local checkpoint information of recovering and started replicas in order to calculate the global checkpoint. As the tracker is updated through recoveries as well, it is easier to reason about the tracker if we can ensure that there are no concurrent recovery attempts for the same target shard (which can happen in case of network disconnects).

2 files changed, 12 insertions, 2 deletions

diff --git a/core/src/main/java/org/elasticsearch/indices/recovery/PeerRecoverySourceService.java b/core/src/main/java/org/elasticsearch/indices/recovery/PeerRecoverySourceService.java
index 7191e4517a..d661713829 100644
--- a/core/src/main/java/org/elasticsearch/indices/recovery/PeerRecoverySourceService.java
+++ b/core/src/main/java/org/elasticsearch/indices/recovery/PeerRecoverySourceService.java
@@ -63,7 +63,7 @@ public class PeerRecoverySourceService extends AbstractComponent implements Inde
 
     private final ClusterService clusterService;
 
-    private final OngoingRecoveries ongoingRecoveries = new OngoingRecoveries();
+    final OngoingRecoveries ongoingRecoveries = new OngoingRecoveries();
 
     @Inject
     public PeerRecoverySourceService(Settings settings, TransportService transportService, IndicesService indicesService,
@@ -137,7 +137,7 @@ public class PeerRecoverySourceService extends AbstractComponent implements Inde
         }
     }
 
-    private final class OngoingRecoveries {
+    final class OngoingRecoveries {
         private final Map<IndexShard, ShardRecoveryContext> ongoingRecoveries = new HashMap<>();
 
         synchronized RecoverySourceHandler addNewRecovery(StartRecoveryRequest request, IndexShard shard) {
@@ -192,6 +192,12 @@ public class PeerRecoverySourceService extends AbstractComponent implements Inde
                 if (onNewRecoveryException != null) {
                     throw onNewRecoveryException;
                 }
+                for (RecoverySourceHandler existingHandler : recoveryHandlers) {
+                    if (existingHandler.getRequest().targetAllocationId().equals(request.targetAllocationId())) {
+                        throw new DelayRecoveryException("recovery with same target already registered, waiting for " +
+                            "previous recovery attempt to be cancelled or completed");
+                    }
+                }
                 RecoverySourceHandler handler = createRecoverySourceHandler(request, shard);
                 recoveryHandlers.add(handler);
                 return handler;
diff --git a/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java b/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
index 3097c8e668..6a39700545 100644
--- a/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
+++ b/core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java
@@ -129,6 +129,10 @@ public class RecoverySourceHandler {
         this.response = new RecoveryResponse();
     }
 
+    public StartRecoveryRequest getRequest() {
+        return request;
+    }
+
     /**
      * performs the recovery from the local engine to the target
      */