Support cloning of searchable snapshot indices (#56595)

Today you can convert a searchable snapshot index back into a regular index by
restoring the underlying snapshot, but this is somewhat wasteful if the shards
are already in cache since it copies the whole index from the repository again.

Instead, we can make use of the locally-cached data by using the clone API to
copy the contents of the cache into the layout expected by a regular shard.
This commit marks the searchable snapshot's private index settings as
`NotCopyableOnResize` so that they are removed by resize operations such as
cloning.

Cloning a regular index typically hard-links the underlying files rather than
copying them, but this is tricky to support in the case of a searchable
snapshot so this commit takes the simpler approach of always copying the
underlying files.

x-pack/plugin/searchable-snapshots/src/main/java/org/elasticsearch/index/store/SearchableSnapshotDirectory.java

@@ -69,6 +69,7 @@
 import java.util.function.Supplier;
 
 import static org.apache.lucene.store.BufferedIndexInput.bufferSize;
+import static org.elasticsearch.index.IndexModule.INDEX_STORE_TYPE_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_CACHE_ENABLED_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_CACHE_EXCLUDED_FILE_TYPES_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_CACHE_PREWARM_ENABLED_SETTING;
@@ -78,6 +79,7 @@
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_SNAPSHOT_NAME_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_UNCACHED_CHUNK_SIZE_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshotsConstants.SEARCHABLE_SNAPSHOTS_THREAD_POOL_NAME;
+import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshotsConstants.SNAPSHOT_DIRECTORY_FACTORY_KEY;
 
 /**
  * Implementation of {@link Directory} that exposes files from a snapshot as a Lucene directory. Because snapshot are immutable this
@@ -438,6 +440,20 @@ public static Directory create(
         ThreadPool threadPool
     ) throws IOException {
 
+        if (SNAPSHOT_REPOSITORY_SETTING.exists(indexSettings.getSettings()) == false
+            || SNAPSHOT_INDEX_ID_SETTING.exists(indexSettings.getSettings()) == false
+            || SNAPSHOT_SNAPSHOT_NAME_SETTING.exists(indexSettings.getSettings()) == false
+            || SNAPSHOT_SNAPSHOT_ID_SETTING.exists(indexSettings.getSettings()) == false) {
+
+            throw new IllegalArgumentException(
+                "directly setting ["
+                    + INDEX_STORE_TYPE_SETTING.getKey()
+                    + "] to ["
+                    + SNAPSHOT_DIRECTORY_FACTORY_KEY
+                    + "] is not permitted; use the mount snapshot API instead"
+            );
+        }
+
         final Repository repository = repositories.repository(SNAPSHOT_REPOSITORY_SETTING.get(indexSettings.getSettings()));
         if (repository instanceof BlobStoreRepository == false) {
             throw new IllegalArgumentException("Repository [" + repository + "] is not searchable");

x-pack/plugin/searchable-snapshots/src/main/java/org/elasticsearch/xpack/searchablesnapshots/SearchableSnapshots.java

@@ -82,46 +82,54 @@ public class SearchableSnapshots extends Plugin implements IndexStorePlugin, Eng
     public static final Setting<String> SNAPSHOT_REPOSITORY_SETTING = Setting.simpleString(
         "index.store.snapshot.repository_name",
         Setting.Property.IndexScope,
-        Setting.Property.PrivateIndex
+        Setting.Property.PrivateIndex,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<String> SNAPSHOT_SNAPSHOT_NAME_SETTING = Setting.simpleString(
         "index.store.snapshot.snapshot_name",
         Setting.Property.IndexScope,
-        Setting.Property.PrivateIndex
+        Setting.Property.PrivateIndex,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<String> SNAPSHOT_SNAPSHOT_ID_SETTING = Setting.simpleString(
         "index.store.snapshot.snapshot_uuid",
         Setting.Property.IndexScope,
-        Setting.Property.PrivateIndex
+        Setting.Property.PrivateIndex,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<String> SNAPSHOT_INDEX_ID_SETTING = Setting.simpleString(
         "index.store.snapshot.index_uuid",
         Setting.Property.IndexScope,
-        Setting.Property.PrivateIndex
+        Setting.Property.PrivateIndex,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<Boolean> SNAPSHOT_CACHE_ENABLED_SETTING = Setting.boolSetting(
         "index.store.snapshot.cache.enabled",
         true,
-        Setting.Property.IndexScope
+        Setting.Property.IndexScope,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<Boolean> SNAPSHOT_CACHE_PREWARM_ENABLED_SETTING = Setting.boolSetting(
         "index.store.snapshot.cache.prewarm.enabled",
         true,
-        Setting.Property.IndexScope
+        Setting.Property.IndexScope,
+        Setting.Property.NotCopyableOnResize
     );
     // The file extensions that are excluded from the cache
     public static final Setting<List<String>> SNAPSHOT_CACHE_EXCLUDED_FILE_TYPES_SETTING = Setting.listSetting(
         "index.store.snapshot.cache.excluded_file_types",
         emptyList(),
         Function.identity(),
         Setting.Property.IndexScope,
-        Setting.Property.NodeScope
+        Setting.Property.NodeScope,
+        Setting.Property.NotCopyableOnResize
     );
     public static final Setting<ByteSizeValue> SNAPSHOT_UNCACHED_CHUNK_SIZE_SETTING = Setting.byteSizeSetting(
         "index.store.snapshot.uncached_chunk_size",
         new ByteSizeValue(-1, ByteSizeUnit.BYTES),
         Setting.Property.IndexScope,
-        Setting.Property.NodeScope
+        Setting.Property.NodeScope,
+        Setting.Property.NotCopyableOnResize
     );
 
     private volatile Supplier<RepositoriesService> repositoriesServiceSupplier;

x-pack/plugin/searchable-snapshots/src/test/java/org/elasticsearch/index/store/SearchableSnapshotDirectoryTests.java

@@ -50,6 +50,7 @@
 import org.elasticsearch.common.lucene.BytesRefs;
 import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.store.ByteArrayIndexInput;
+import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeUnit;
 import org.elasticsearch.common.unit.ByteSizeValue;
@@ -99,6 +100,10 @@
 import static java.util.Collections.emptyMap;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_CACHE_ENABLED_SETTING;
 import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_CACHE_PREWARM_ENABLED_SETTING;
+import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_INDEX_ID_SETTING;
+import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_REPOSITORY_SETTING;
+import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_SNAPSHOT_ID_SETTING;
+import static org.elasticsearch.xpack.searchablesnapshots.SearchableSnapshots.SNAPSHOT_SNAPSHOT_NAME_SETTING;
 import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
@@ -683,6 +688,32 @@ public void testClearCache() throws Exception {
         }
     }
 
+    public void testRequiresAdditionalSettings() {
+        final List<Setting<String>> requiredSettings = org.elasticsearch.common.collect.List.of(
+            SNAPSHOT_REPOSITORY_SETTING,
+            SNAPSHOT_INDEX_ID_SETTING,
+            SNAPSHOT_SNAPSHOT_NAME_SETTING,
+            SNAPSHOT_SNAPSHOT_ID_SETTING
+        );
+
+        for (int i = 0; i < requiredSettings.size(); i++) {
+            final Settings.Builder settings = Settings.builder()
+                .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+                .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT);
+            for (int j = 0; j < requiredSettings.size(); j++) {
+                if (i != j) {
+                    settings.put(requiredSettings.get(j).getKey(), randomAlphaOfLength(10));
+                }
+            }
+            final IndexSettings indexSettings = new IndexSettings(IndexMetadata.builder("test").settings(settings).build(), Settings.EMPTY);
+            expectThrows(
+                IllegalArgumentException.class,
+                () -> SearchableSnapshotDirectory.create(null, null, indexSettings, null, null, null)
+            );
+        }
+    }
+
     private static <T> void assertThat(
         String reason,
         IndexInput actual,
@@ -727,4 +758,5 @@ private static IndexSettings newIndexSettings() {
                 .build()
         );
     }
+
 }

x-pack/plugin/searchable-snapshots/src/test/java/org/elasticsearch/xpack/searchablesnapshots/SearchableSnapshotsIntegTests.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.action.admin.cluster.snapshots.create.CreateSnapshotResponse;
 import org.elasticsearch.action.admin.cluster.snapshots.restore.RestoreSnapshotResponse;
 import org.elasticsearch.action.admin.indices.recovery.RecoveryResponse;
+import org.elasticsearch.action.admin.indices.shrink.ResizeType;
 import org.elasticsearch.action.index.IndexRequestBuilder;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.node.DiscoveryNode;
@@ -69,6 +70,7 @@ public class SearchableSnapshotsIntegTests extends BaseSearchableSnapshotsIntegT
     public void testCreateAndRestoreSearchableSnapshot() throws Exception {
         final String fsRepoName = randomAlphaOfLength(10);
         final String indexName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
+        final String aliasName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
         final String restoredIndexName = randomBoolean() ? indexName : randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
         final String snapshotName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
 
@@ -84,6 +86,8 @@ public void testCreateAndRestoreSearchableSnapshot() throws Exception {
         // Peer recovery always copies .liv files but we do not permit writing to searchable snapshot directories so this doesn't work, but
         // we can bypass this by forcing soft deletes to be used. TODO this restriction can be lifted when #55142 is resolved.
         assertAcked(prepareCreate(indexName, Settings.builder().put(INDEX_SOFT_DELETES_SETTING.getKey(), true)));
+        assertAcked(client().admin().indices().prepareAliases().addAlias(indexName, aliasName));
+
         final List<IndexRequestBuilder> indexRequestBuilders = new ArrayList<>();
         for (int i = between(10, 10_000); i >= 0; i--) {
             indexRequestBuilders.add(client().prepareIndex(indexName, "_doc").setSource("foo", randomBoolean() ? "bar" : "baz"));
@@ -178,8 +182,14 @@ public void testCreateAndRestoreSearchableSnapshot() throws Exception {
         assertRecovered(restoredIndexName, originalAllHits, originalBarHits);
         assertSearchableSnapshotStats(restoredIndexName, cacheEnabled, nonCachedExtensions);
 
+        assertThat(client().admin().indices().prepareGetAliases(aliasName).get().getAliases().size(), equalTo(0));
+        assertAcked(client().admin().indices().prepareAliases().addAlias(restoredIndexName, aliasName));
+        assertThat(client().admin().indices().prepareGetAliases(aliasName).get().getAliases().size(), equalTo(1));
+        assertRecovered(aliasName, originalAllHits, originalBarHits, false);
+
         internalCluster().fullRestart();
         assertRecovered(restoredIndexName, originalAllHits, originalBarHits);
+        assertRecovered(aliasName, originalAllHits, originalBarHits, false);
         assertSearchableSnapshotStats(restoredIndexName, cacheEnabled, nonCachedExtensions);
 
         internalCluster().ensureAtLeastNumDataNodes(2);
@@ -217,6 +227,46 @@ public void testCreateAndRestoreSearchableSnapshot() throws Exception {
 
         assertRecovered(restoredIndexName, originalAllHits, originalBarHits);
         assertSearchableSnapshotStats(restoredIndexName, cacheEnabled, nonCachedExtensions);
+
+        assertAcked(
+            client().admin()
+                .indices()
+                .prepareUpdateSettings(restoredIndexName)
+                .setSettings(
+                    Settings.builder()
+                        .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 1)
+                        .putNull(IndexMetadata.INDEX_ROUTING_REQUIRE_GROUP_SETTING.getConcreteSettingForNamespace("_name").getKey())
+                )
+        );
+
+        final String clonedIndexName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
+        assertAcked(
+            client().admin()
+                .indices()
+                .prepareResizeIndex(restoredIndexName, clonedIndexName)
+                .setResizeType(ResizeType.CLONE)
+                .setSettings(Settings.builder().putNull(IndexModule.INDEX_STORE_TYPE_SETTING.getKey()).build())
+        );
+        ensureGreen(clonedIndexName);
+        assertRecovered(clonedIndexName, originalAllHits, originalBarHits, false);
+
+        final Settings clonedIndexSettings = client().admin()
+            .indices()
+            .prepareGetSettings(clonedIndexName)
+            .get()
+            .getIndexToSettings()
+            .get(clonedIndexName);
+        assertFalse(clonedIndexSettings.hasValue(IndexModule.INDEX_STORE_TYPE_SETTING.getKey()));
+        assertFalse(clonedIndexSettings.hasValue(SearchableSnapshots.SNAPSHOT_REPOSITORY_SETTING.getKey()));
+        assertFalse(clonedIndexSettings.hasValue(SearchableSnapshots.SNAPSHOT_SNAPSHOT_NAME_SETTING.getKey()));
+        assertFalse(clonedIndexSettings.hasValue(SearchableSnapshots.SNAPSHOT_SNAPSHOT_ID_SETTING.getKey()));
+        assertFalse(clonedIndexSettings.hasValue(SearchableSnapshots.SNAPSHOT_INDEX_ID_SETTING.getKey()));
+
+        assertAcked(client().admin().indices().prepareDelete(restoredIndexName));
+        assertThat(client().admin().indices().prepareGetAliases(aliasName).get().getAliases().size(), equalTo(0));
+        assertAcked(client().admin().indices().prepareAliases().addAlias(clonedIndexName, aliasName));
+        assertRecovered(aliasName, originalAllHits, originalBarHits, false);
+
     }
 
     public void testCanMountSnapshotTakenWhileConcurrentlyIndexing() throws Exception {
@@ -376,6 +426,12 @@ public void testMaxRestoreBytesPerSecIsUsed() throws Exception {
     }
 
     private void assertRecovered(String indexName, TotalHits originalAllHits, TotalHits originalBarHits) throws Exception {
+        assertRecovered(indexName, originalAllHits, originalBarHits, true);
+    }
+
+    private void assertRecovered(String indexName, TotalHits originalAllHits, TotalHits originalBarHits, boolean checkRecoveryStats)
+        throws Exception {
+
         final Thread[] threads = new Thread[between(1, 5)];
         final AtomicArray<TotalHits> allHits = new AtomicArray<>(threads.length);
         final AtomicArray<TotalHits> barHits = new AtomicArray<>(threads.length);
@@ -406,12 +462,17 @@ private void assertRecovered(String indexName, TotalHits originalAllHits, TotalH
         ensureGreen(indexName);
         latch.countDown();
 
-        final RecoveryResponse recoveryResponse = client().admin().indices().prepareRecoveries(indexName).get();
-        for (List<RecoveryState> recoveryStates : recoveryResponse.shardRecoveryStates().values()) {
-            for (RecoveryState recoveryState : recoveryStates) {
-                logger.info("Checking {}[{}]", recoveryState.getShardId(), recoveryState.getPrimary() ? "p" : "r");
-                assertThat(recoveryState.getIndex().recoveredFileCount(), lessThanOrEqualTo(1)); // we make a new commit so we write a new
-                                                                                                 // `segments_n` file
+        if (checkRecoveryStats) {
+            final RecoveryResponse recoveryResponse = client().admin().indices().prepareRecoveries(indexName).get();
+            for (List<RecoveryState> recoveryStates : recoveryResponse.shardRecoveryStates().values()) {
+                for (RecoveryState recoveryState : recoveryStates) {
+                    logger.info("Checking {}[{}]", recoveryState.getShardId(), recoveryState.getPrimary() ? "p" : "r");
+                    assertThat(
+                        Strings.toString(recoveryState), // we make a new commit so we write a new `segments_n` file
+                        recoveryState.getIndex().recoveredFileCount(),
+                        lessThanOrEqualTo(1)
+                    );
+                }
             }
         }