Introduce soft-deletes retention policy based on global checkpoint (#…

…30335)

This commit introduces a soft-deletes retention merge policy based on
the global checkpoint. Some notes on this simple retention policy:

- This policy keeps all operations whose seq# is greater than the 
persisted global checkpoint and configurable extra operations prior to
the global checkpoint. This is good enough for querying history changes.

- This policy is not watertight for peer-recovery. We send the 
safe-commit in peer-recovery, thus we need to also send all operations
after the local checkpoint of that commit. This is analog to the min
translog generation for recovery.

- This policy is too simple to support rollback.

Relates #29530

server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java

@@ -131,6 +131,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
         ShardsLimitAllocationDecider.INDEX_TOTAL_SHARDS_PER_NODE_SETTING,
         IndexSettings.INDEX_GC_DELETES_SETTING,
         IndexSettings.INDEX_SOFT_DELETES_SETTING,
+        IndexSettings.INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING,
         IndicesRequestCache.INDEX_CACHE_REQUEST_ENABLED_SETTING,
         UnassignedInfo.INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING,
         EnableAllocationDecider.INDEX_ROUTING_REBALANCE_ENABLE_SETTING,

server/src/main/java/org/elasticsearch/index/IndexSettings.java

@@ -242,6 +242,14 @@ public final class IndexSettings {
      */
     public static final Setting<Boolean> INDEX_SOFT_DELETES_SETTING = Setting.boolSetting("index.soft_deletes", true, Property.IndexScope);
 
+    /**
+     * Controls how many soft-deleted documents will be kept around before being merged away. Keeping more deleted
+     * documents increases the chance of operation-based recoveries and allows querying a longer history of documents.
+     * If soft-deletes is enabled, an engine by default will retain all operations up to the global checkpoint.
+     **/
+    public static final Setting<Long> INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING =
+        Setting.longSetting("index.soft_deletes.retention.operations", 0, 0, Property.IndexScope, Property.Dynamic);
+
     /**
      * The maximum number of refresh listeners allows on this shard.
      */
@@ -287,6 +295,7 @@ public final class IndexSettings {
     private final IndexScopedSettings scopedSettings;
     private long gcDeletesInMillis = DEFAULT_GC_DELETES.millis();
     private final boolean softDeleteEnabled;
+    private volatile long softDeleteRetentionOperations;
     private volatile boolean warmerEnabled;
     private volatile int maxResultWindow;
     private volatile int maxInnerResultWindow;
@@ -398,6 +407,7 @@ public IndexSettings(final IndexMetaData indexMetaData, final Settings nodeSetti
         mergeSchedulerConfig = new MergeSchedulerConfig(this);
         gcDeletesInMillis = scopedSettings.get(INDEX_GC_DELETES_SETTING).getMillis();
         softDeleteEnabled = version.onOrAfter(Version.V_7_0_0_alpha1) && scopedSettings.get(INDEX_SOFT_DELETES_SETTING);
+        softDeleteRetentionOperations = scopedSettings.get(INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING);
         warmerEnabled = scopedSettings.get(INDEX_WARMER_ENABLED_SETTING);
         maxResultWindow = scopedSettings.get(MAX_RESULT_WINDOW_SETTING);
         maxInnerResultWindow = scopedSettings.get(MAX_INNER_RESULT_WINDOW_SETTING);
@@ -455,6 +465,7 @@ public IndexSettings(final IndexMetaData indexMetaData, final Settings nodeSetti
         scopedSettings.addSettingsUpdateConsumer(DEFAULT_FIELD_SETTING, this::setDefaultFields);
         scopedSettings.addSettingsUpdateConsumer(INDEX_SEARCH_IDLE_AFTER, this::setSearchIdleAfter);
         scopedSettings.addSettingsUpdateConsumer(MAX_REGEX_LENGTH_SETTING, this::setMaxRegexLength);
+        scopedSettings.addSettingsUpdateConsumer(INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING, this::setSoftDeleteRetentionOperations);
     }
 
     private void setSearchIdleAfter(TimeValue searchIdleAfter) { this.searchIdleAfter = searchIdleAfter; }
@@ -837,4 +848,15 @@ public boolean isExplicitRefresh() {
     public boolean isSoftDeleteEnabled() {
         return softDeleteEnabled;
     }
+
+    private void setSoftDeleteRetentionOperations(long ops) {
+        this.softDeleteRetentionOperations = ops;
+    }
+
+    /**
+     * Returns the number of extra operations (i.e. soft-deleted documents) to be kept for recoveries and history purpose.
+     */
+    public long getSoftDeleteRetentionOperations() {
+        return this.softDeleteRetentionOperations;
+    }
 }

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

@@ -22,6 +22,7 @@
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.apache.lucene.document.Field;
+import org.apache.lucene.document.LongPoint;
 import org.apache.lucene.document.NumericDocValuesField;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.IndexCommit;
@@ -34,8 +35,10 @@
 import org.apache.lucene.index.MergePolicy;
 import org.apache.lucene.index.SegmentCommitInfo;
 import org.apache.lucene.index.SegmentInfos;
+import org.apache.lucene.index.SoftDeletesRetentionMergePolicy;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.Query;
 import org.apache.lucene.search.ReferenceManager;
 import org.apache.lucene.search.SearcherFactory;
 import org.apache.lucene.search.SearcherManager;
@@ -2002,8 +2005,8 @@ private IndexWriterConfig getIndexWriterConfig() {
         // background merges
         MergePolicy mergePolicy = config().getMergePolicy();
         if (softDeleteEnabled) {
-            // TODO: soft-delete retention policy
             iwc.setSoftDeletesField(Lucene.SOFT_DELETE_FIELD);
+            mergePolicy = new SoftDeletesRetentionMergePolicy(Lucene.SOFT_DELETE_FIELD, this::softDeletesRetentionQuery, mergePolicy);
         }
         iwc.setMergePolicy(new ElasticsearchMergePolicy(mergePolicy));
         iwc.setSimilarity(engineConfig.getSimilarity());
@@ -2016,6 +2019,20 @@ private IndexWriterConfig getIndexWriterConfig() {
         return iwc;
     }
 
+    /**
+     * Documents including tombstones are soft-deleted and matched this query will be retained and won't cleaned up by merges.
+     */
+    private Query softDeletesRetentionQuery() {
+        ensureOpen();
+        // TODO: We send the safe commit in peer-recovery, thus we need to retain all operations after the local checkpoint of that commit.
+        final long retainedExtraOps = engineConfig.getIndexSettings().getSoftDeleteRetentionOperations();
+        // Prefer using the global checkpoint which is persisted on disk than an in-memory value.
+        // If we failed to fsync checkpoint but already used a higher global checkpoint value to clean up soft-deleted ops,
+        // then we may not have all required operations whose seq# greater than the global checkpoint after restarted.
+        final long persistedGlobalCheckpoint = translog.getLastSyncedGlobalCheckpoint();
+        return LongPoint.newRangeQuery(SeqNoFieldMapper.NAME, persistedGlobalCheckpoint + 1 - retainedExtraOps, Long.MAX_VALUE);
+    }
+
     /** Extended SearcherFactory that warms the segments if needed when acquiring a new searcher */
     static final class SearchFactory extends EngineSearcherFactory {
         private final Engine.Warmer warmer;

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

@@ -123,6 +123,7 @@
 import org.elasticsearch.index.translog.Translog;
 import org.elasticsearch.index.translog.TranslogConfig;
 import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
+import org.elasticsearch.test.IndexSettingsModule;
 import org.hamcrest.MatcherAssert;
 import org.hamcrest.Matchers;
 
@@ -178,6 +179,7 @@
 import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.isIn;
 import static org.hamcrest.Matchers.lessThanOrEqualTo;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.notNullValue;
@@ -251,8 +253,9 @@ public void testVersionMapAfterAutoIDDocument() throws IOException {
     }
 
     public void testSegments() throws Exception {
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
         try (Store store = createStore();
-             InternalEngine engine = createEngine(defaultSettings, store, createTempDir(), NoMergePolicy.INSTANCE)) {
+             InternalEngine engine = createEngine(config(defaultSettings, store, createTempDir(), NoMergePolicy.INSTANCE, null, null, globalCheckpoint::get))) {
             List<Segment> segments = engine.segments(false);
             assertThat(segments.isEmpty(), equalTo(true));
             assertThat(engine.segmentsStats(false).getCount(), equalTo(0L));
@@ -324,6 +327,8 @@ public void testSegments() throws Exception {
 
 
             engine.delete(new Engine.Delete("test", "1", newUid(doc), primaryTerm.get()));
+            globalCheckpoint.set(engine.getLocalCheckpointTracker().getCheckpoint());
+            engine.getTranslog().sync();
             engine.refresh("test");
 
             segments = engine.segments(false);
@@ -1279,9 +1284,13 @@ public void testVersioningNewIndex() throws IOException {
         assertThat(indexResult.getVersion(), equalTo(1L));
     }
 
-    public void testForceMerge() throws IOException {
+    public void testForceMergeWithoutSoftDeletes() throws IOException {
+        Settings settings = Settings.builder()
+            .put(defaultSettings.getSettings())
+            .put(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), false).build();
+        IndexMetaData indexMetaData = IndexMetaData.builder(defaultSettings.getIndexMetaData()).settings(settings).build();
         try (Store store = createStore();
-             Engine engine = createEngine(config(defaultSettings, store, createTempDir(),
+             Engine engine = createEngine(config(IndexSettingsModule.newIndexSettings(indexMetaData), store, createTempDir(),
                  new LogByteSizeMergePolicy(), null))) { // use log MP here we test some behavior in ESMP
             int numDocs = randomIntBetween(10, 100);
             for (int i = 0; i < numDocs; i++) {
@@ -1322,6 +1331,66 @@ public void testForceMerge() throws IOException {
         }
     }
 
+    public void testForceMergeWithSoftDeletesRetention() throws Exception {
+        final long retainedExtraOps = randomLongBetween(0, 10);
+        Settings.Builder settings = Settings.builder()
+            .put(defaultSettings.getSettings())
+            .put(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), true)
+            .put(IndexSettings.INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING.getKey(), retainedExtraOps);
+        final IndexMetaData indexMetaData = IndexMetaData.builder(defaultSettings.getIndexMetaData()).settings(settings).build();
+        final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetaData);
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+        final MapperService mapperService = createMapperService("test");
+        final Set<String> liveDocs = new HashSet<>();
+        try (Store store = createStore();
+             Engine engine = createEngine(config(indexSettings, store, createTempDir(), newMergePolicy(), null, null, globalCheckpoint::get))) {
+            int numDocs = scaledRandomIntBetween(10, 100);
+            for (int i = 0; i < numDocs; i++) {
+                ParsedDocument doc = testParsedDocument(Integer.toString(i), null, testDocument(), B_1, null);
+                engine.index(indexForDoc(doc));
+                liveDocs.add(doc.id());
+            }
+            for (int i = 0; i < numDocs; i++) {
+                ParsedDocument doc = testParsedDocument(Integer.toString(i), null, testDocument(), B_1, null);
+                if (randomBoolean()) {
+                    engine.delete(new Engine.Delete(doc.type(), doc.id(), newUid(doc.id()), primaryTerm.get()));
+                    liveDocs.remove(doc.id());
+                }
+                if (randomBoolean()) {
+                    engine.index(indexForDoc(doc));
+                    liveDocs.add(doc.id());
+                }
+            }
+            long localCheckpoint = engine.getLocalCheckpointTracker().getCheckpoint();
+            globalCheckpoint.set(randomLongBetween(0, localCheckpoint));
+            engine.getTranslog().sync();
+            engine.forceMerge(true, 1, false, false, false);
+            assertConsistentHistoryBetweenTranslogAndLuceneIndex(engine, mapperService);
+            Map<Long, Translog.Operation> ops = readAllOperationsInLucene(engine, mapperService)
+                .stream().collect(Collectors.toMap(Translog.Operation::seqNo, Function.identity()));
+            for (long seqno = 0; seqno <= localCheckpoint; seqno++) {
+                long keptIndex = globalCheckpoint.get() + 1 - retainedExtraOps;
+                String msg = "seq# [" + seqno + "], global checkpoint [" + globalCheckpoint + "], retained-ops [" + retainedExtraOps + "]";
+                if (seqno < keptIndex) {
+                    Translog.Operation op = ops.get(seqno);
+                    if (op != null) {
+                        assertThat(op, instanceOf(Translog.Index.class));
+                        assertThat(msg, ((Translog.Index) op).id(), isIn(liveDocs));
+                    }
+                } else {
+                    assertThat(msg, ops.get(seqno), notNullValue());
+                }
+            }
+            settings.put(IndexSettings.INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING.getKey(), 0);
+            indexSettings.updateIndexMetaData(IndexMetaData.builder(defaultSettings.getIndexMetaData()).settings(settings).build());
+            globalCheckpoint.set(localCheckpoint);
+            engine.getTranslog().sync();
+            engine.forceMerge(true, 1, false, false, false);
+            assertConsistentHistoryBetweenTranslogAndLuceneIndex(engine, mapperService);
+            assertThat(readAllOperationsInLucene(engine, mapperService), hasSize(liveDocs.size()));
+        }
+    }
+
     public void testForceMergeAndClose() throws IOException, InterruptedException {
         int numIters = randomIntBetween(2, 10);
         for (int j = 0; j < numIters; j++) {
@@ -2525,14 +2594,16 @@ public void testSkipTranslogReplay() throws IOException {
             Engine.IndexResult indexResult = engine.index(firstIndexRequest);
             assertThat(indexResult.getVersion(), equalTo(1L));
         }
+        EngineConfig config = engine.config();
         assertVisibleCount(engine, numDocs);
         engine.close();
-        trimUnsafeCommits(engine.config());
-        engine = new InternalEngine(engine.config());
-        engine.skipTranslogRecovery();
-        try (Engine.Searcher searcher = engine.acquireSearcher("test")) {
-            TopDocs topDocs = searcher.searcher().search(new MatchAllDocsQuery(), randomIntBetween(numDocs, numDocs + 10));
-            assertThat(topDocs.totalHits, equalTo(0L));
+        trimUnsafeCommits(config);
+        try (InternalEngine engine = new InternalEngine(config)) {
+            engine.skipTranslogRecovery();
+            try (Engine.Searcher searcher = engine.acquireSearcher("test")) {
+                TopDocs topDocs = searcher.searcher().search(new MatchAllDocsQuery(), randomIntBetween(numDocs, numDocs + 10));
+                assertThat(topDocs.totalHits, equalTo(0L));
+            }
         }
     }
 

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -2350,7 +2350,16 @@ public void testDocStats() throws IOException {
                 deleteDoc(indexShard, "_doc", id);
                 indexDoc(indexShard, "_doc", id);
             }
-
+            // Need to update and sync the global checkpoint as the soft-deletes retention MergePolicy depends on it.
+            if (indexShard.indexSettings.isSoftDeleteEnabled()) {
+                if (indexShard.routingEntry().primary()) {
+                    indexShard.updateGlobalCheckpointForShard(indexShard.routingEntry().allocationId().getId(),
+                        indexShard.getLocalCheckpoint());
+                } else {
+                    indexShard.updateGlobalCheckpointOnReplica(indexShard.getLocalCheckpoint(), "test");
+                }
+                indexShard.sync();
+            }
             // flush the buffered deletes
             final FlushRequest flushRequest = new FlushRequest();
             flushRequest.force(false);
@@ -2910,6 +2919,7 @@ public void testSegmentMemoryTrackedInBreaker() throws Exception {
 
         // Deleting a doc causes its memory to be freed from the breaker
         deleteDoc(primary, "_doc", "0");
+        primary.sync(); // need to sync global checkpoint as the soft-deletes retention MergePolicy depends on it.
         primary.refresh("force refresh");
 
         ss = primary.segmentStats(randomBoolean());

server/src/test/java/org/elasticsearch/indices/stats/IndexStatsIT.java

@@ -43,13 +43,15 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.IndexModule;
+import org.elasticsearch.index.IndexService;
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.MergePolicyConfig;
 import org.elasticsearch.index.MergeSchedulerConfig;
 import org.elasticsearch.index.VersionType;
 import org.elasticsearch.index.cache.query.QueryCacheStats;
 import org.elasticsearch.index.engine.VersionConflictEngineException;
 import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.index.shard.IndexShard;
 import org.elasticsearch.index.translog.Translog;
 import org.elasticsearch.indices.IndicesQueryCache;
 import org.elasticsearch.indices.IndicesRequestCache;
@@ -69,6 +71,7 @@
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Random;
+import java.util.Set;
 import java.util.concurrent.BrokenBarrierException;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
@@ -1005,10 +1008,15 @@ private void assertCumulativeQueryCacheStats(IndicesStatsResponse response) {
     }
 
     public void testFilterCacheStats() throws Exception {
-        assertAcked(prepareCreate("index").setSettings(Settings.builder().put(indexSettings()).put("number_of_replicas", 0).build()).get());
-        indexRandom(true,
+        Settings settings = Settings.builder().put(indexSettings()).put("number_of_replicas", 0).build();
+        assertAcked(prepareCreate("index").setSettings(settings).get());
+        indexRandom(false, true,
                 client().prepareIndex("index", "type", "1").setSource("foo", "bar"),
                 client().prepareIndex("index", "type", "2").setSource("foo", "baz"));
+        if (IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings)) {
+            persistGlobalCheckpoint("index"); // Need to persist the global checkpoint for the soft-deletes retention MP.
+        }
+        refresh();
         ensureGreen();
 
         IndicesStatsResponse response = client().admin().indices().prepareStats("index").setQueryCache(true).get();
@@ -1039,6 +1047,9 @@ public void testFilterCacheStats() throws Exception {
 
         assertEquals(DocWriteResponse.Result.DELETED, client().prepareDelete("index", "type", "1").get().getResult());
         assertEquals(DocWriteResponse.Result.DELETED, client().prepareDelete("index", "type", "2").get().getResult());
+        if (IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings)) {
+            persistGlobalCheckpoint("index"); // Need to persist the global checkpoint for the soft-deletes retention MP.
+        }
         refresh();
         response = client().admin().indices().prepareStats("index").setQueryCache(true).get();
         assertCumulativeQueryCacheStats(response);
@@ -1172,4 +1183,21 @@ public void testConcurrentIndexingAndStatsRequests() throws BrokenBarrierExcepti
         assertThat(executionFailures.get(), emptyCollectionOf(Exception.class));
     }
 
+
+    /**
+     * Persist the global checkpoint on all shards of the given index into disk.
+     * This makes sure that the persisted global checkpoint on those shards will equal to the in-memory value.
+     */
+    private void persistGlobalCheckpoint(String index) throws Exception {
+        final Set<String> nodes = internalCluster().nodesInclude(index);
+        for (String node : nodes) {
+            final IndicesService indexServices = internalCluster().getInstance(IndicesService.class, node);
+            for (IndexService indexService : indexServices) {
+                for (IndexShard indexShard : indexService) {
+                    indexShard.sync();
+                    assertThat(indexShard.getLastSyncedGlobalCheckpoint(), equalTo(indexShard.getGlobalCheckpoint()));
+                }
+            }
+        }
+    }
 }