IGNITE-25502 fail node on index greater than current majority

modules/partition-replicator/src/main/java/org/apache/ignite/internal/partition/replicator/raft/ZonePartitionRaftListener.java

@@ -412,6 +412,12 @@ public void onShutdown() {
         }
     }
 
+    @Override
+    public long getPersistedAppliedIndex() {
+        // Clamp to 0 because lastAppliedIndex() returns -1 during rebalance.
+        return max(0, txStateStorage.lastAppliedIndex());
+    }
+
     /**
      * Adds a given Table Partition-level Raft processor to the set of managed processors.
      *

modules/raft-api/src/main/java/org/apache/ignite/internal/raft/service/RaftGroupListener.java

@@ -96,4 +96,14 @@ default void onConfigurationCommitted(
      * Invoked once after a raft node has been shut down.
      */
     void onShutdown();
+
+    /**
+     * Returns the last applied index persisted by the state machine.
+     * Called during {@code NodeImpl.init()} to prevent truncation of already-applied log entries.
+     *
+     * @return persisted applied index, or 0 if unknown.
+     */
+    default long getPersistedAppliedIndex() {
+        return 0;
+    }
 }

modules/raft/src/main/java/org/apache/ignite/internal/raft/server/impl/JraftServerImpl.java

@@ -870,6 +870,11 @@ public RaftGroupListener getListener() {
             return listener;
         }
 
+        @Override
+        public long getPersistedAppliedIndex() {
+            return listener.getPersistedAppliedIndex();
+        }
+
         @Override
         public void onApply(Iterator iter) {
             var iterWrapper = new WriteCommandIterator(iter, marshaller);

modules/raft/src/main/java/org/apache/ignite/raft/jraft/StateMachine.java

@@ -133,4 +133,14 @@ default void onRawConfigurationCommitted(ConfigurationEntry conf, long lastAppli
      * @param ctx context of leader change
      */
     void onStartFollowing(final LeaderChangeContext ctx);
+
+    /**
+     * Returns the last applied index persisted by the state machine.
+     * Called during {@code NodeImpl.init()} to prevent truncation of already-applied log entries.
+     *
+     * @return persisted applied index, or 0 if unknown.
+     */
+    default long getPersistedAppliedIndex() {
+        return 0;
+    }
 }

modules/raft/src/main/java/org/apache/ignite/raft/jraft/core/NodeImpl.java

@@ -1066,6 +1066,19 @@ public boolean init(final NodeOptions opts) {
             return false;
         }
 
+        // Restore appliedId so that unsafeTruncateSuffix() can reject truncation of applied entries.
+        long persistedApplied = this.options.getFsm().getPersistedAppliedIndex();
+        if (persistedApplied > 0) {
+            long term = this.logManager.getTerm(persistedApplied);
+            if (term > 0) {
+                // Term is 0 when the index is outside the log (covered by a snapshot) — skip in that case.
+                this.logManager.setAppliedId(new LogId(persistedApplied, term));
+            } else {
+                LOG.warn("Node {} persisted applied index {} is not in the raft log, expecting snapshot to cover it.",
+                        getNodeId(), persistedApplied);
+            }
+        }
+
         final Status st = this.logManager.checkConsistency();
         if (!st.isOk()) {
             LOG.error("Node {} is initialized with inconsistent log, status={}.", getNodeId(), st);

modules/raft/src/main/java/org/apache/ignite/raft/jraft/storage/impl/LogManagerImpl.java

@@ -1049,11 +1049,25 @@ private boolean reset(final long nextLogIndex) {
         }
     }
 
-    private void unsafeTruncateSuffix(final long lastIndexKept, final Lock lock) {
+    /**
+     * Truncates log entries after {@code lastIndexKept}.
+     *
+     * @return {@code true} on success, {@code false} if truncation would discard applied entries (node moves to error state).
+     */
+    private boolean unsafeTruncateSuffix(final long lastIndexKept, final Lock lock) {
         if (lastIndexKept < this.appliedId.getIndex()) {
-            LOG.error("FATAL ERROR: Can't truncate logs before appliedId={}, lastIndexKept={}", this.appliedId,
-                lastIndexKept);
-            return;
+            LOG.error("Raft log suffix conflict: cannot truncate entries that have been applied to the state machine. "
+                    + "nodeId={}, appliedId={}, lastIndexKept={}. The partition will be moved to error state.",
+                    this.nodeId, this.appliedId, lastIndexKept);
+            lock.unlock();
+            try {
+                reportError(RaftError.EINVAL.getNumber(),
+                        "Raft log suffix conflict: attempted to truncate applied entries, appliedId=%s, lastIndexKept=%d",
+                        this.appliedId, lastIndexKept);
+            } finally {
+                lock.lock();
+            }
+            return false;
         }
 
         this.logsInMemory.removeFromLastWhen(entry -> entry.getId().getIndex() > lastIndexKept);
@@ -1068,6 +1082,7 @@ private void unsafeTruncateSuffix(final long lastIndexKept, final Lock lock) {
         final TruncateSuffixClosure c = new TruncateSuffixClosure(lastIndexKept, lastTermKept);
         offerEvent(c, EventType.TRUNCATE_SUFFIX);
         lock.lock();
+        return true;
     }
 
     @SuppressWarnings("NonAtomicOperationOnVolatileField")
@@ -1121,7 +1136,11 @@ private boolean checkAndResolveConflict(final List<LogEntry> entries, final Stab
                     if (entries.get(conflictingIndex).getId().getIndex() <= this.lastLogIndex) {
                         // Truncate all the conflicting entries to make local logs
                         // consensus with the leader.
-                        unsafeTruncateSuffix(entries.get(conflictingIndex).getId().getIndex() - 1, lock);
+                        if (!unsafeTruncateSuffix(entries.get(conflictingIndex).getId().getIndex() - 1, lock)) {
+                            Utils.runClosureInThread(nodeOptions.getCommonExecutor(), done,
+                                new Status(RaftError.EINVAL, "Raft log suffix conflict with applied entries"));
+                            return false;
+                        }
                     }
                     this.lastLogIndex = lastLogEntry.getId().getIndex();
                 } // else this is a duplicated AppendEntriesRequest, we have

modules/raft/src/test/java/org/apache/ignite/raft/jraft/storage/impl/LogManagerTest.java

@@ -23,9 +23,14 @@
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.apache.ignite.internal.testframework.matchers.CompletableFutureMatcher.willBe;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.mockito.Mockito.verify;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import org.apache.ignite.internal.thread.IgniteThreadFactory;
@@ -40,6 +45,7 @@
 import org.apache.ignite.raft.jraft.entity.EnumOutter;
 import org.apache.ignite.raft.jraft.entity.LogEntry;
 import org.apache.ignite.raft.jraft.entity.LogId;
+import org.apache.ignite.raft.jraft.error.RaftException;
 import org.apache.ignite.raft.jraft.entity.NodeId;
 import org.apache.ignite.raft.jraft.entity.PeerId;
 import org.apache.ignite.raft.jraft.entity.RaftOutter;
@@ -476,4 +482,46 @@ public void testLastLogIndexWhenShutdown() throws Exception {
         Exception e = assertThrows(IllegalStateException.class, () -> this.logManager.getLastLogIndex(true));
         assertEquals("Node is shutting down", e.getMessage());
     }
+
+    /** Suffix truncation below appliedId must report error and abort the append (IGNITE-25502). */
+    @Test
+    public void testSuffixTruncationBelowAppliedIndexReportsError() {
+        List<LogEntry> entries = new ArrayList<>();
+        for (int i = 1; i <= 10; i++) {
+            entries.add(TestUtils.mockEntry(i, 1));
+        }
+        assertThat("Initial entries should be appended successfully", appendEntries(entries), willBe(true));
+        assertEquals(10, this.logManager.getLastLogIndex());
+
+        this.logManager.getLastLogId(true); // Flush disruptor so setDiskId() completes.
+        this.logManager.setAppliedId(new LogId(8, 1));
+
+        // Conflicting entries at index 6+ (term 2 vs existing term 1) trigger unsafeTruncateSuffix(5).
+        // Since 5 < appliedId.index (8), this must be rejected.
+        List<LogEntry> conflicting = new ArrayList<>();
+        for (int i = 6; i <= 12; i++) {
+            conflicting.add(TestUtils.mockEntry(i, 2));
+        }
+        assertThat("Append should fail due to suffix conflict with applied entries", appendEntries(conflicting), willBe(false));
+
+        verify(fsmCaller).onError(any(RaftException.class));
+        assertEquals(10, this.logManager.getLastLogIndex());
+
+        for (int i = 1; i <= 10; i++) {
+            LogEntry entry = this.logManager.getEntry(i);
+            assertEquals(i, entry.getId().getIndex());
+            assertEquals(1, entry.getId().getTerm());
+        }
+    }
+
+    private CompletableFuture<Boolean> appendEntries(List<LogEntry> entries) {
+        CompletableFuture<Boolean> future = new CompletableFuture<>();
+        this.logManager.appendEntries(new ArrayList<>(entries), new LogManager.StableClosure() {
+            @Override
+            public void run(Status status) {
+                future.complete(status.isOk());
+            }
+        });
+        return future;
+    }
 }

modules/runner/src/integrationTest/java/org/apache/ignite/internal/ItTruncateRaftLogAndRestartNodesTest.java

@@ -23,8 +23,10 @@
 import static org.apache.ignite.internal.testframework.flow.TestFlowUtils.subscribeToList;
 import static org.apache.ignite.internal.testframework.matchers.CompletableFutureMatcher.willCompleteSuccessfully;
 import static org.apache.ignite.internal.util.CompletableFutures.allOf;
+import static org.awaitility.Awaitility.await;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.arrayWithSize;
+import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.hasSize;
@@ -72,13 +74,13 @@
 import org.apache.ignite.internal.util.IgniteUtils;
 import org.apache.ignite.raft.jraft.conf.ConfigurationManager;
 import org.apache.ignite.raft.jraft.core.NodeImpl;
+import org.apache.ignite.raft.jraft.core.State;
 import org.apache.ignite.raft.jraft.option.LogStorageOptions;
 import org.apache.ignite.raft.jraft.option.NodeOptions;
 import org.apache.ignite.raft.jraft.option.RaftOptions;
 import org.apache.ignite.raft.jraft.storage.LogStorage;
 import org.apache.ignite.tx.TransactionOptions;
 import org.hamcrest.Matchers;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -98,7 +100,6 @@ protected int initialNodes() {
         return 0;
     }
 
-    @Disabled("https://issues.apache.org/jira/browse/IGNITE-25502")
     @Test
     void enterNodeWithIndexGreaterThanCurrentMajority() throws Exception {
         cluster.startAndInit(3);
@@ -148,12 +149,21 @@ void enterNodeWithIndexGreaterThanCurrentMajority() throws Exception {
 
             startNode(2);
 
+            // Node 2 has applied entries that the new majority (nodes 0, 1) doesn't have,
+            // so it must go to ERROR state when the leader tries to overwrite those entries.
+            await()
+                    .timeout(10, TimeUnit.SECONDS)
+                    .untilAsserted(() ->
+                            assertThat(raftNodeImpl(2, replicationGroup).getState(), equalTo(State.STATE_ERROR))
+                    );
+
+            // SQL should still work via the healthy majority.
             assertThat(
                     toPeopleFromSqlRows(executeSql(selectPeopleDml(TABLE_NAME))),
                     arrayWithSize(Matchers.allOf(greaterThan(0), lessThan(people.length)))
             );
 
-            for (int nodeIndex = 0; nodeIndex < 3; nodeIndex++) {
+            for (int nodeIndex = 0; nodeIndex < 2; nodeIndex++) {
                 assertThat(
                         "nodeIndex=" + nodeIndex,
                         scanPeopleFromAllPartitions(nodeIndex, TABLE_NAME),