Pass transient extra data on new commits

server/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -377,13 +377,21 @@ public interface IndexCommitListener {
          * {@link IndexCommitRef} prevents the {@link IndexCommitRef} files to be deleted from disk until the reference is closed. As such,
          * the listener must close the reference as soon as it is done with it.
          *
-         * @param shardId         the {@link ShardId} of shard
-         * @param store           the index shard store
-         * @param primaryTerm     the shard's primary term value
-         * @param indexCommitRef  a reference on the newly created index commit
-         * @param additionalFiles the set of filenames that are added by the new commit
+         * @param shardId            the {@link ShardId} of shard
+         * @param store              the index shard store
+         * @param primaryTerm        the shard's primary term value
+         * @param indexCommitRef     a reference on the newly created index commit
+         * @param additionalFiles    the set of filenames that are added by the new commit
+         * @param extraTransientData extra transient data relevant to the new commit
          */
-        void onNewCommit(ShardId shardId, Store store, long primaryTerm, IndexCommitRef indexCommitRef, Set<String> additionalFiles);
+        void onNewCommit(
+            ShardId shardId,
+            Store store,
+            long primaryTerm,
+            IndexCommitRef indexCommitRef,
+            Set<String> additionalFiles,
+            Map<String, String> extraTransientData
+        );
 
         /**
          * This method is invoked after the policy deleted the given {@link IndexCommit}. A listener is never notified of a deleted commit

server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -395,7 +395,14 @@ public void onNewAcquiredCommit(final IndexCommit commit, final Set<String> addi
                     final IndexCommitRef indexCommitRef = acquireIndexCommitRef(() -> commit);
                     var primaryTerm = config().getPrimaryTermSupplier().getAsLong();
                     assert indexCommitRef.getIndexCommit() == commit;
-                    wrappedListener.onNewCommit(shardId, store, primaryTerm, indexCommitRef, additionalFiles);
+                    wrappedListener.onNewCommit(
+                        shardId,
+                        store,
+                        primaryTerm,
+                        indexCommitRef,
+                        additionalFiles,
+                        getCommitExtraTransientData()
+                    );
                 }
 
                 @Override
@@ -416,7 +423,8 @@ public void onNewCommit(
                 Store store,
                 long primaryTerm,
                 IndexCommitRef indexCommitRef,
-                Set<String> additionalFiles
+                Set<String> additionalFiles,
+                Map<String, String> extraTransientData
             ) {
                 final long nextGen = indexCommitRef.getIndexCommit().getGeneration();
                 final long prevGen = generation.getAndSet(nextGen);
@@ -427,7 +435,7 @@ public void onNewCommit(
                         + prevGen
                         + " for shard "
                         + shardId;
-                listener.onNewCommit(shardId, store, primaryTerm, indexCommitRef, additionalFiles);
+                listener.onNewCommit(shardId, store, primaryTerm, indexCommitRef, additionalFiles, extraTransientData);
             }
 
             @Override
@@ -2980,6 +2988,14 @@ protected Map<String, String> getCommitExtraUserData(final long localCheckpoint)
         return Collections.emptyMap();
     }
 
+    /**
+     * Allows InternalEngine extenders to return custom key-value pairs for transient information, that is not stored in the commit, to be
+     * included in the {@link org.elasticsearch.index.engine.Engine.IndexCommitListener}'s new commit invocation.
+     */
+    protected Map<String, String> getCommitExtraTransientData() {
+        return Collections.emptyMap();
+    }
+
     final void ensureCanFlush() {
         // translog recovery happens after the engine is fully constructed.
         // If we are in this stage we have to prevent flushes from this

server/src/test/java/org/elasticsearch/index/IndexModuleTests.java

@@ -686,7 +686,8 @@ public void onNewCommit(
                 Store store,
                 long primaryTerm,
                 Engine.IndexCommitRef indexCommitRef,
-                Set<String> additionalFiles
+                Set<String> additionalFiles,
+                Map<String, String> extraTransientData
             ) {
                 lastAcquiredPrimaryTerm.set(primaryTerm);
                 lastAcquiredCommit.set(indexCommitRef);

server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -7419,7 +7419,8 @@ public void onNewCommit(
                 Store store,
                 long primaryTerm,
                 Engine.IndexCommitRef indexCommitRef,
-                Set<String> additionalFiles
+                Set<String> additionalFiles,
+                Map<String, String> extraTransientData
             ) {
                 assertNotNull(store);
                 assertTrue(store.hasReferences());