Refactor the new snapshot code in Engine (elastic#95364)

Relates ES-5058

Revert "Ability to add extra user data for lucene commits (elastic#95073)"
This reverts commit 192b4aa.

Relates ES-5849

Author: kingherc

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

@@ -538,7 +538,7 @@ private void recoverFromTranslogInternal(TranslogRecoveryRunner translogRecovery
         final int opsRecovered;
         final long localCheckpoint = getProcessedLocalCheckpoint();
         if (localCheckpoint < recoverUpToSeqNo) {
-            try (Translog.Snapshot snapshot = translog.newSnapshot(localCheckpoint + 1, recoverUpToSeqNo)) {
+            try (Translog.Snapshot snapshot = newTranslogSnapshot(localCheckpoint + 1, recoverUpToSeqNo)) {
                 opsRecovered = translogRecoveryRunner.run(this, snapshot);
             } catch (Exception e) {
                 throw new EngineException(shardId, "failed to recover from translog", e);
@@ -561,6 +561,10 @@ private void recoverFromTranslogInternal(TranslogRecoveryRunner translogRecovery
         translog.trimUnreferencedReaders();
     }
 
+    protected Translog.Snapshot newTranslogSnapshot(long fromSeqNo, long toSeqNo) throws IOException {
+        return translog.newSnapshot(fromSeqNo, toSeqNo);
+    }
+
     private Translog openTranslog(
         EngineConfig engineConfig,
         TranslogDeletionPolicy translogDeletionPolicy,
@@ -2666,20 +2670,6 @@ protected void doRun() throws Exception {
         }
     }
 
-    /**
-     * Defines extra user data to be stored in a commit file.
-     *
-     * Note that:
-     * <ul>
-     *  <li>Any conflicting keys used internally by the engine or the store will prevail.</li>
-     *  <li>The extra user data will not be present in an empty commit.</li>
-     *  <li>This function is temporary and may be removed in the future.</li>
-     * </ul>
-     */
-    protected Map<String, String> getCommitExtraUserData() {
-        return Map.of();
-    }
-
     /**
      * Commits the specified index writer.
      *
@@ -2700,9 +2690,7 @@ protected void commitIndexWriter(final IndexWriter writer, final Translog transl
                  * {@link IndexWriter#commit()} call flushes all documents, we defer computation of the maximum sequence number to the time
                  * of invocation of the commit data iterator (which occurs after all documents have been flushed to Lucene).
                  */
-                final Map<String, String> extraCommitUserData = getCommitExtraUserData();
-                final Map<String, String> commitData = Maps.newMapWithExpectedSize(8 + extraCommitUserData.size());
-                commitData.putAll(extraCommitUserData);
+                final Map<String, String> commitData = Maps.newMapWithExpectedSize(8);
                 commitData.put(Translog.TRANSLOG_UUID_KEY, translog.getTranslogUUID());
                 commitData.put(SequenceNumbers.LOCAL_CHECKPOINT_KEY, Long.toString(localCheckpoint));
                 commitData.put(SequenceNumbers.MAX_SEQ_NO, Long.toString(localCheckpointTracker.getMaxSeqNo()));

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

@@ -196,7 +196,6 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
-import static org.hamcrest.Matchers.hasEntry;
 import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.hasSize;
@@ -7402,25 +7401,6 @@ public void testCurrentVersionIsCommitted() throws IOException {
         }
     }
 
-    public void testExtraUserDataIsCommitted() throws IOException {
-        engine.close();
-        engine = new InternalEngine(engine.config()) {
-            @Override
-            protected Map<String, String> getCommitExtraUserData() {
-                return Map.of("userkey", "userdata", ES_VERSION, Version.V_EMPTY.toString());
-            }
-        };
-        engine.skipTranslogRecovery();
-
-        ParsedDocument doc = testParsedDocument("1", null, testDocumentWithTextField(), SOURCE, null);
-        engine.index(indexForDoc(doc));
-        engine.flush();
-
-        Map<String, String> userData = engine.getLastCommittedSegmentInfos().getUserData();
-        assertThat(userData, hasEntry("userkey", "userdata"));
-        assertThat(userData, hasEntry(ES_VERSION, Version.CURRENT.toString()));
-    }
-
     public void testTrimUnsafeCommitHasESVersionInUserData() throws IOException {
         final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
         final int maxSeqNo = 40;