From 2c5efd2e610cfdfe9212e938b8bdd59fc6f3fedc Mon Sep 17 00:00:00 2001
From: Keith Massey <keith.massey@elastic.co>
Date: Wed, 11 Dec 2024 13:38:04 -0600
Subject: [PATCH] Correcting the index version filter in migration reindex
 logic (#118487)

---
 .../action/ReindexDataStreamAction.java        | 18 ++++++++++++++++++
 .../ReindexDataStreamTransportAction.java      |  6 ++----
 ...eindexDataStreamPersistentTaskExecutor.java |  4 +++-
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamAction.java b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamAction.java
index 9e4cbb1082215..39d4170f6e712 100644
--- a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamAction.java
+++ b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamAction.java
@@ -13,10 +13,14 @@
 import org.elasticsearch.action.ActionType;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.support.IndicesOptions;
+import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.util.FeatureFlag;
 import org.elasticsearch.features.NodeFeature;
+import org.elasticsearch.index.Index;
+import org.elasticsearch.index.IndexVersion;
+import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.ToXContent;
@@ -39,10 +43,24 @@ public class ReindexDataStreamAction extends ActionType<ReindexDataStreamAction.
     public static final ParseField SOURCE_FIELD = new ParseField("source");
     public static final ParseField INDEX_FIELD = new ParseField("index");
 
+    /*
+     * The version before which we do not support writes in the _next_ major version of Elasticsearch. For example, Elasticsearch 10.x will
+     * not support writing to indices created before version 9.0.0.
+     */
+    private static final IndexVersion MINIMUM_WRITEABLE_VERSION_AFTER_UPGRADE = IndexVersions.UPGRADE_TO_LUCENE_10_0_0;
+
     public ReindexDataStreamAction() {
         super(NAME);
     }
 
+    /*
+     * This predicate allows through only indices that were created with a previous lucene version, meaning that they need to be reindexed
+     * in order to be writable in the _next_ lucene version.
+     */
+    public static Predicate<Index> getOldIndexVersionPredicate(Metadata metadata) {
+        return index -> metadata.index(index).getCreationVersion().onOrBefore(MINIMUM_WRITEABLE_VERSION_AFTER_UPGRADE);
+    }
+
     public enum Mode {
         UPGRADE
     }
diff --git a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamTransportAction.java b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamTransportAction.java
index 95a078690a055..f011c429ce79c 100644
--- a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamTransportAction.java
+++ b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/ReindexDataStreamTransportAction.java
@@ -27,6 +27,7 @@
 import org.elasticsearch.xpack.migrate.task.ReindexDataStreamTaskParams;
 
 import static org.elasticsearch.xpack.migrate.action.ReindexDataStreamAction.TASK_ID_PREFIX;
+import static org.elasticsearch.xpack.migrate.action.ReindexDataStreamAction.getOldIndexVersionPredicate;
 
 /*
  * This transport action creates a new persistent task for reindexing the source data stream given in the request. On successful creation
@@ -67,10 +68,7 @@ protected void doExecute(Task task, ReindexDataStreamRequest request, ActionList
             return;
         }
         int totalIndices = dataStream.getIndices().size();
-        int totalIndicesToBeUpgraded = (int) dataStream.getIndices()
-            .stream()
-            .filter(index -> metadata.index(index).getCreationVersion().isLegacyIndexVersion())
-            .count();
+        int totalIndicesToBeUpgraded = (int) dataStream.getIndices().stream().filter(getOldIndexVersionPredicate(metadata)).count();
         ReindexDataStreamTaskParams params = new ReindexDataStreamTaskParams(
             sourceDataStreamName,
             transportService.getThreadPool().absoluteTimeInMillis(),
diff --git a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/task/ReindexDataStreamPersistentTaskExecutor.java b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/task/ReindexDataStreamPersistentTaskExecutor.java
index fc471cfa89f26..7ec5014b9edff 100644
--- a/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/task/ReindexDataStreamPersistentTaskExecutor.java
+++ b/x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/task/ReindexDataStreamPersistentTaskExecutor.java
@@ -24,6 +24,8 @@
 import java.util.List;
 import java.util.Map;
 
+import static org.elasticsearch.xpack.migrate.action.ReindexDataStreamAction.getOldIndexVersionPredicate;
+
 public class ReindexDataStreamPersistentTaskExecutor extends PersistentTasksExecutor<ReindexDataStreamTaskParams> {
     private static final TimeValue TASK_KEEP_ALIVE_TIME = TimeValue.timeValueDays(1);
     private final Client client;
@@ -72,7 +74,7 @@ protected void nodeOperation(AllocatedPersistentTask task, ReindexDataStreamTask
             if (dataStreamInfos.size() == 1) {
                 List<Index> indices = dataStreamInfos.getFirst().getDataStream().getIndices();
                 List<Index> indicesToBeReindexed = indices.stream()
-                    .filter(index -> clusterService.state().getMetadata().index(index).getCreationVersion().isLegacyIndexVersion())
+                    .filter(getOldIndexVersionPredicate(clusterService.state().metadata()))
                     .toList();
                 reindexDataStreamTask.setPendingIndicesCount(indicesToBeReindexed.size());
                 for (Index index : indicesToBeReindexed) {