From 9ac90e7b81de791c575cf2346cec194c02a22ebd Mon Sep 17 00:00:00 2001
From: Grant Palau Spencer <gspencer@linkedin.com>
Date: Thu, 27 Mar 2025 16:28:56 -0700
Subject: [PATCH] Fall back to current states when best possible calculation
 fails

---
 .../stages/BestPossibleStateCalcStage.java           | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/helix-core/src/main/java/org/apache/helix/controller/stages/BestPossibleStateCalcStage.java b/helix-core/src/main/java/org/apache/helix/controller/stages/BestPossibleStateCalcStage.java
index 152c766e43..62e6f35d20 100644
--- a/helix-core/src/main/java/org/apache/helix/controller/stages/BestPossibleStateCalcStage.java
+++ b/helix-core/src/main/java/org/apache/helix/controller/stages/BestPossibleStateCalcStage.java
@@ -321,6 +321,18 @@ private BestPossibleStateOutput compute(ClusterEvent event, Map<String, Resource
             .format("Failed to calculate best possible states for %d resources.",
                 failureResources.size()));
 
+    // Fall back to current states for resources that cannot be computed
+    failureResources.parallelStream().forEach(resourceName -> {
+      if (currentStateOutput.getCurrentStateMap(resourceName).isEmpty()) {
+        return;
+      }
+      IdealState fakeIS = new IdealState(resourceName);
+      currentStateOutput.getCurrentStateMap(resourceName).forEach((partition, stateMap) ->
+          fakeIS.setInstanceStateMap(partition.getPartitionName(), stateMap != null ? stateMap : new HashMap<>())
+      );
+      updateBestPossibleStateOutput(output, resourceMap.get(resourceName), fakeIS);
+    });
+
     return output;
   }