fix refresh

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

@@ -1420,6 +1420,7 @@ final void refresh(String source, SearcherScope scope) throws EngineException {
         // since it flushes the index as well (though, in terms of concurrency, we are allowed to do it)
         // both refresh types will result in an internal refresh but only the external will also
         // pass the new reader reference to the external reader manager.
+        final long localCheckpointBeforeRefresh = getLocalCheckpoint();
 
         // this will also cause version map ram to be freed hence we always account for it.
         final long bytes = indexWriter.ramBytesUsed() + versionMap.ramBytesUsedForRefresh();
@@ -1445,6 +1446,7 @@ final void refresh(String source, SearcherScope scope) throws EngineException {
                 } finally {
                     store.decRef();
                 }
+                lastRefreshedCheckpointListener.updateRefreshedCheckpoint(localCheckpointBeforeRefresh);
             }
         } catch (AlreadyClosedException e) {
             failOnTragicEvent(e);
@@ -1459,7 +1461,8 @@ final void refresh(String source, SearcherScope scope) throws EngineException {
         }  finally {
             writingBytes.addAndGet(-bytes);
         }
-
+        assert lastRefreshedCheckpoint() >= localCheckpointBeforeRefresh : "refresh checkpoint was not advanced; " +
+            "local_checkpoint=" + localCheckpointBeforeRefresh + " refresh_checkpoint=" + lastRefreshedCheckpoint();
         // TODO: maybe we should just put a scheduled job in threadPool?
         // We check for pruning in each delete request, but we also prune here e.g. in case a delete burst comes in and then no more deletes
         // for a long time:
@@ -2526,21 +2529,31 @@ public long softUpdateDocuments(Term term, Iterable<? extends Iterable<? extends
     final long lastRefreshedCheckpoint() {
         return lastRefreshedCheckpointListener.refreshedCheckpoint.get();
     }
+
     private final class LastRefreshedCheckpointListener implements ReferenceManager.RefreshListener {
         final AtomicLong refreshedCheckpoint;
         private long pendingCheckpoint;
+
         LastRefreshedCheckpointListener(long initialLocalCheckpoint) {
             this.refreshedCheckpoint = new AtomicLong(initialLocalCheckpoint);
         }
+
         @Override
         public void beforeRefresh() {
-            pendingCheckpoint = localCheckpointTracker.getCheckpoint(); // All change until this point should be visible after refresh
+            // all changes until this point should be visible after refresh
+            pendingCheckpoint = localCheckpointTracker.getCheckpoint();
         }
+
         @Override
         public void afterRefresh(boolean didRefresh) {
             if (didRefresh) {
-                refreshedCheckpoint.set(pendingCheckpoint);
+                updateRefreshedCheckpoint(pendingCheckpoint);
             }
         }
+
+        void updateRefreshedCheckpoint(long checkpoint) {
+            refreshedCheckpoint.updateAndGet(curr -> Math.max(curr, checkpoint));
+            assert refreshedCheckpoint.get() >= checkpoint : refreshedCheckpoint.get() + " < " + checkpoint;
+        }
     }
 }

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

@@ -4994,6 +4994,32 @@ public void testKeepMinRetainedSeqNoByMergePolicy() throws IOException {
         }
     }
 
+    public void testLastRefreshCheckpoint() throws Exception {
+        AtomicBoolean done = new AtomicBoolean();
+        Thread[] refreshThreads = new Thread[between(1, 8)];
+        CountDownLatch latch = new CountDownLatch(refreshThreads.length);
+        for (int i = 0; i < refreshThreads.length; i++) {
+            latch.countDown();
+            refreshThreads[i] = new Thread(() -> {
+                while (done.get() == false) {
+                    long checkPointBeforeRefresh = engine.getLocalCheckpoint();
+                    engine.refresh("test", randomFrom(Engine.SearcherScope.values()));
+                    assertThat(engine.lastRefreshedCheckpoint(), greaterThanOrEqualTo(checkPointBeforeRefresh));
+                }
+            });
+            refreshThreads[i].start();
+        }
+        latch.await();
+        List<Engine.Operation> ops = generateSingleDocHistory(true, VersionType.EXTERNAL, 1, 10, 1000, "1");
+        concurrentlyApplyOps(ops, engine);
+        done.set(true);
+        for (Thread thread : refreshThreads) {
+            thread.join();
+        }
+        engine.refresh("test");
+        assertThat(engine.lastRefreshedCheckpoint(), equalTo(engine.getLocalCheckpoint()));
+    }
+
     private static void trimUnsafeCommits(EngineConfig config) throws IOException {
         final Store store = config.getStore();
         final TranslogConfig translogConfig = config.getTranslogConfig();