Soft-deletes policy should always fetch latest leases (#37940)

If a new retention lease is added while a primary's soft-deletes policy
is locked for peer-recovery, that lease won't be baked into the Lucene
commit.

Relates #37165
Relates #37375

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

@@ -46,7 +46,6 @@ final class SoftDeletesPolicy {
     private long retentionOperations;
     // The min seq_no value that is retained - ops after this seq# should exist in the Lucene index.
     private long minRetainedSeqNo;
-    private Collection<RetentionLease> retentionLeases;
     // provides the retention leases used to calculate the minimum sequence number to retain
     private final Supplier<Collection<RetentionLease>> retentionLeasesSupplier;
 
@@ -59,7 +58,6 @@ final class SoftDeletesPolicy {
         this.retentionOperations = retentionOperations;
         this.minRetainedSeqNo = minRetainedSeqNo;
         this.retentionLeasesSupplier = Objects.requireNonNull(retentionLeasesSupplier);
-        retentionLeases = retentionLeasesSupplier.get();
         this.localCheckpointOfSafeCommit = SequenceNumbers.NO_OPS_PERFORMED;
         this.retentionLockCount = 0;
     }
@@ -113,6 +111,11 @@ synchronized long getMinRetainedSeqNo() {
     }
 
     public synchronized Tuple<Long, Collection<RetentionLease>> getRetentionPolicy() {
+        /*
+         * When an engine is flushed, we need to provide it the latest collection of retention leases even when the soft deletes policy is
+         * locked for peer recovery.
+         */
+        final Collection<RetentionLease> retentionLeases = retentionLeasesSupplier.get();
         // do not advance if the retention lock is held
         if (retentionLockCount == 0) {
             /*
@@ -126,7 +129,6 @@ public synchronized Tuple<Long, Collection<RetentionLease>> getRetentionPolicy()
              */
 
             // calculate the minimum sequence number to retain based on retention leases
-            retentionLeases = retentionLeasesSupplier.get();
             final long minimumRetainingSequenceNumber = retentionLeases
                     .stream()
                     .mapToLong(RetentionLease::retainingSequenceNumber)

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

@@ -24,18 +24,21 @@
 import org.apache.lucene.search.Query;
 import org.elasticsearch.common.lease.Releasable;
 import org.elasticsearch.index.seqno.RetentionLease;
-import org.elasticsearch.index.seqno.SequenceNumbers;
 import org.elasticsearch.test.ESTestCase;
 
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Supplier;
 
+import static org.elasticsearch.index.seqno.SequenceNumbers.NO_OPS_PERFORMED;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 
@@ -46,7 +49,7 @@ public class SoftDeletesPolicyTests extends ESTestCase  {
      */
     public void testSoftDeletesRetentionLock() {
         long retainedOps = between(0, 10000);
-        AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+        AtomicLong globalCheckpoint = new AtomicLong(NO_OPS_PERFORMED);
         final AtomicLong[] retainingSequenceNumbers = new AtomicLong[randomIntBetween(0, 8)];
         for (int i = 0; i < retainingSequenceNumbers.length; i++) {
             retainingSequenceNumbers[i] = new AtomicLong();
@@ -116,4 +119,23 @@ public void testSoftDeletesRetentionLock() {
         assertThat(policy.getMinRetainedSeqNo(), equalTo(minRetainedSeqNo));
     }
 
+    public void testAlwaysFetchLatestRetentionLeases() {
+        final AtomicLong globalCheckpoint = new AtomicLong(NO_OPS_PERFORMED);
+        final Collection<RetentionLease> leases = new ArrayList<>();
+        final int numLeases = randomIntBetween(0, 10);
+        for (int i = 0; i < numLeases; i++) {
+            leases.add(new RetentionLease(Integer.toString(i), randomLongBetween(0, 1000), randomNonNegativeLong(), "test"));
+        }
+        final Supplier<Collection<RetentionLease>> leasesSupplier = () -> Collections.unmodifiableCollection(new ArrayList<>(leases));
+        final SoftDeletesPolicy policy =
+                new SoftDeletesPolicy(globalCheckpoint::get, randomIntBetween(1, 1000), randomIntBetween(0, 1000), leasesSupplier);
+        if (randomBoolean()) {
+            policy.acquireRetentionLock();
+        }
+        if (numLeases == 0) {
+            assertThat(policy.getRetentionPolicy().v2(), empty());
+        } else {
+            assertThat(policy.getRetentionPolicy().v2(), contains(leases.toArray(new RetentionLease[0])));
+        }
+    }
 }

server/src/test/java/org/elasticsearch/index/seqno/RetentionLeaseSyncIT.java

@@ -32,6 +32,7 @@
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.threadpool.ThreadPool;
 
+import java.io.Closeable;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
@@ -70,8 +71,11 @@ public void testRetentionLeasesSyncedOnAdd() throws Exception {
             final String source = randomAlphaOfLength(8);
             final CountDownLatch latch = new CountDownLatch(1);
             final ActionListener<ReplicationResponse> listener = ActionListener.wrap(r -> latch.countDown(), e -> fail(e.toString()));
+            // simulate a peer-recovery which locks the soft-deletes policy on the primary.
+            final Closeable retentionLock = randomBoolean() ? primary.acquireRetentionLockForPeerRecovery() : () -> {};
             currentRetentionLeases.put(id, primary.addRetentionLease(id, retainingSequenceNumber, source, listener));
             latch.await();
+            retentionLock.close();
 
             // check retention leases have been committed on the primary
             final Collection<RetentionLease> primaryCommittedRetentionLeases = RetentionLease.decodeRetentionLeases(