Rewrite IndexMetadata update

Author: ankikuma

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -202,7 +202,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion RERANKER_FAILURES_ALLOWED = def(9_013_0_00);
     public static final TransportVersion VOYAGE_AI_INTEGRATION_ADDED = def(9_014_0_00);
     // making this large for now to avoid merge conflicts
-    public static final TransportVersion UNASSIGENEDINFO_SHARD_ADDED = def(9_020_0_00);
+    public static final TransportVersion UNASSIGENEDINFO_RESHARD_ADDED = def(9_020_0_00);
 
     /*
      * STOP! READ THIS FIRST! No, really,

server/src/main/java/org/elasticsearch/action/admin/indices/autoshard/AutoshardIndexClusterStateUpdateRequest.java

@@ -12,7 +12,7 @@
 import org.elasticsearch.action.support.ActiveShardCount;
 
 /**
- * Cluster state update request that allows to re-shard an index
+ * Cluster state update request that allows re-sharding an index
  * At the moment, we only have the ability to increment the number of shards
  * of an index (by a multiplicative factor).
  * We do not support removing shards from an index.

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -949,6 +949,7 @@ public IndexMetadata withIncrementedPrimaryTerm(int shardId) {
      * Q: Is it ok to set routingNumShards to shardCount ?
      * Q: Should we increment this.version here ?
      */
+    /*
     public IndexMetadata withIncrementedPrimaryShards(int shardCount) {
         if (this.primaryTerms.length == shardCount) return this;
 
@@ -1016,6 +1017,7 @@ public IndexMetadata withIncrementedPrimaryShards(int shardCount) {
             this.shardSizeInBytesForecast
         );
     }
+    */
 
     /**
      * @param timestampRange new @timestamp range
@@ -2031,6 +2033,34 @@ public Builder numberOfShards(int numberOfShards) {
             return this;
         }
 
+        /** Builder to create IndexMetadata that has an increased shard count (used for re-shard).
+         * The new shard count must be a multiple of the original shardcount.
+         * We do not support shrinking the shard count.
+         * @param shardCount   updated shardCount
+         */
+        public Builder reshardAddShards (int shardCount) {
+            // Assert routingNumShards is null ?
+            // Assert numberOfShards > 0
+            if (shardCount % numberOfShards() != 0) {
+                throw new IllegalArgumentException(
+                    "New shard count ["
+                        + shardCount
+                        + "] should be a multiple"
+                        + " of current shard count ["
+                        + numberOfShards()
+                        + "] for ["
+                        + index
+                        + "]"
+                );
+            }
+            settings = Settings.builder().put(settings).put(SETTING_NUMBER_OF_SHARDS, shardCount).build();
+            var newPrimaryTerms = new long[shardCount];
+            System.arraycopy(primaryTerms, 0, newPrimaryTerms, 0, this.primaryTerms.length);
+            primaryTerms = newPrimaryTerms;
+            routingNumShards = shardCount;
+            return this;
+        }
+
         /**
          * Sets the number of shards that should be used for routing. This should only be used if the number of shards in
          * an index has changed ie if the index is shrunk.

server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java

@@ -2177,9 +2177,11 @@ public Builder updateNumberOfShards(final int numberOfShards, final String index
             if (indexMetadata == null) {
                 throw new IndexNotFoundException(index);
             }
-            IndexMetadata newIndexMetadata = indexMetadata.withIncrementedPrimaryShards(numberOfShards);
-            put(IndexMetadata.builder(newIndexMetadata).numberOfShards(numberOfShards));
-
+            // IndexMetadata newIndexMetadata = indexMetadata.withIncrementedPrimaryShards(numberOfShards);
+            // put(IndexMetadata.builder(newIndexMetadata).numberOfShards(numberOfShards));
+            put(IndexMetadata.builder(indexMetadata)
+                .settingsVersion(indexMetadata.getSettingsVersion() + 1)
+                .reshardAddShards(numberOfShards));
             return this;
         }
 

server/src/main/java/org/elasticsearch/cluster/routing/RoutingTable.java

@@ -482,7 +482,7 @@ public Builder updateNumberOfShards(final int newShardCount, final String index)
                     shardId,
                     true,
                     RecoverySource.EmptyStoreRecoverySource.INSTANCE,
-                    new UnassignedInfo(UnassignedInfo.Reason.SHARD_ADDED, null), // A new Reason needed in UnassignedInfo
+                    new UnassignedInfo(UnassignedInfo.Reason.RESHARD_ADDED, null), // A new Reason needed in UnassignedInfo
                     ShardRouting.Role.INDEX_ONLY
                 ); // A new role API similar to newReplicaRole() needed in shardRoutingRoleStrategy ?
                 IndexShardRoutingTable.Builder indexShardRoutingBuilder = IndexShardRoutingTable.builder(shardId);

server/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java

@@ -179,7 +179,7 @@ public enum Reason {
         /**
          * New shard added as part of index re-sharding operation
          */
-        SHARD_ADDED
+        RESHARD_ADDED
     }
 
     /**
@@ -339,7 +339,7 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeByte((byte) Reason.NODE_LEFT.ordinal());
         } else if (reason.equals(Reason.UNPROMOTABLE_REPLICA) && out.getTransportVersion().before(VERSION_UNPROMOTABLE_REPLICA_ADDED)) {
             out.writeByte((byte) Reason.PRIMARY_FAILED.ordinal());
-        } else if (reason.equals(Reason.SHARD_ADDED) && out.getTransportVersion().before(TransportVersions.UNASSIGENEDINFO_SHARD_ADDED)) {
+        } else if (reason.equals(Reason.RESHARD_ADDED) && out.getTransportVersion().before(TransportVersions.UNASSIGENEDINFO_RESHARD_ADDED)) {
             out.writeByte((byte) Reason.FORCED_EMPTY_PRIMARY.ordinal());
         } else {
             out.writeByte((byte) reason.ordinal());

server/src/test/java/org/elasticsearch/cluster/routing/UnassignedInfoTests.java

@@ -86,7 +86,7 @@ public void testReasonOrdinalOrder() {
             UnassignedInfo.Reason.INDEX_CLOSED,
             UnassignedInfo.Reason.NODE_RESTARTING,
             UnassignedInfo.Reason.UNPROMOTABLE_REPLICA,
-            UnassignedInfo.Reason.SHARD_ADDED };
+            UnassignedInfo.Reason.RESHARD_ADDED };
         for (int i = 0; i < order.length; i++) {
             assertThat(order[i].ordinal(), equalTo(i));
         }