Enable soft-deletes by default for 7.0+ indices (#38929)

Today when users upgrade to 7.0, existing indices will automatically
switch to soft-deletes without an opt-out option. With this change, 
we only enable soft-deletes by default for new indices.

Relates #36141

Author: dnhatn

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

@@ -243,9 +243,11 @@ public final class IndexSettings {
 
     /**
      * Specifies if the index should use soft-delete instead of hard-delete for update/delete operations.
+     * Soft-deletes is enabled by default for 7.0+ indices.
      */
-    public static final Setting<Boolean> INDEX_SOFT_DELETES_SETTING =
-        Setting.boolSetting("index.soft_deletes.enabled", true, Property.IndexScope, Property.Final);
+    public static final Setting<Boolean> INDEX_SOFT_DELETES_SETTING = Setting.boolSetting("index.soft_deletes.enabled",
+        settings -> Boolean.toString(IndexMetaData.SETTING_INDEX_VERSION_CREATED.get(settings).onOrAfter(Version.V_7_0_0)),
+        Property.IndexScope, Property.Final);
 
     /**
      * Controls how many soft-deleted documents will be kept around before being merged away. Keeping more deleted

server/src/test/java/org/elasticsearch/index/IndexSettingsTests.java

@@ -561,4 +561,20 @@ public void testUpdateSoftDeletesFails() {
                 Settings.builder(), Settings.builder(), "index"));
         assertThat(error.getMessage(), equalTo("final index setting [index.soft_deletes.enabled], not updateable"));
     }
+
+    public void testSoftDeletesDefaultSetting() {
+        // enabled by default on 7.0+ or later
+        {
+            Version createdVersion = VersionUtils.randomVersionBetween(random(), Version.V_7_0_0, Version.CURRENT);
+            Settings settings = Settings.builder().put(IndexMetaData.SETTING_INDEX_VERSION_CREATED.getKey(), createdVersion).build();
+            assertTrue(IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings));
+        }
+        // disabled by default on the previous versions
+        {
+            Version prevVersion = VersionUtils.randomVersionBetween(
+                random(), Version.V_6_5_0, VersionUtils.getPreviousVersion(Version.V_7_0_0));
+            Settings settings = Settings.builder().put(IndexMetaData.SETTING_INDEX_VERSION_CREATED.getKey(), prevVersion).build();
+            assertFalse(IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings));
+        }
+    }
 }

server/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java

@@ -2210,10 +2210,11 @@ public void testSnapshotMoreThanOnce() throws ExecutionException, InterruptedExc
         {
             SnapshotStatus snapshotStatus = client.admin().cluster().prepareSnapshotStatus("test-repo")
                 .setSnapshots("test-2").get().getSnapshots().get(0);
+            Settings settings = client.admin().indices().prepareGetSettings("test").get().getIndexToSettings().get("test");
             List<SnapshotIndexShardStatus> shards = snapshotStatus.getShards();
             for (SnapshotIndexShardStatus status : shards) {
                 // we flush before the snapshot such that we have to process the segments_N files plus the .del file
-                if (INDEX_SOFT_DELETES_SETTING.get(indexSettings)) {
+                if (INDEX_SOFT_DELETES_SETTING.get(settings)) {
                     // soft-delete generates DV files.
                     assertThat(status.getStats().getProcessedFileCount(), greaterThan(2));
                 } else {

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinator.java

@@ -11,7 +11,6 @@
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ExceptionsHelper;
-import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateRequest;
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
@@ -448,9 +447,7 @@ private void checkAutoFollowPattern(String autoFollowPattenName,
                     }
                 } else {
                     final Settings leaderIndexSettings = remoteMetadata.getIndexSafe(indexToFollow).getSettings();
-                    if (leaderIndexSettings.getAsBoolean(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(),
-                        IndexMetaData.SETTING_INDEX_VERSION_CREATED.get(leaderIndexSettings).onOrAfter(Version.V_7_0_0)) == false) {
-
+                    if (IndexSettings.INDEX_SOFT_DELETES_SETTING.get(leaderIndexSettings) == false) {
                         String message = String.format(Locale.ROOT, "index [%s] cannot be followed, because soft deletes are not enabled",
                             indexToFollow.getName());
                         LOGGER.warn(message);

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/TransportPutFollowAction.java

@@ -9,7 +9,6 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.message.ParameterizedMessage;
-import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.admin.cluster.snapshots.restore.RestoreClusterStateListener;
 import org.elasticsearch.action.admin.cluster.snapshots.restore.RestoreSnapshotRequest;
@@ -124,9 +123,7 @@ private void createFollowerIndex(
             listener.onFailure(new IllegalArgumentException("leader index [" + request.getLeaderIndex() + "] does not exist"));
             return;
         }
-        // soft deletes are enabled by default on indices created on 7.0.0 or later
-        if (leaderIndexMetaData.getSettings().getAsBoolean(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(),
-            IndexMetaData.SETTING_INDEX_VERSION_CREATED.get(leaderIndexMetaData.getSettings()).onOrAfter(Version.V_7_0_0)) == false) {
+        if (IndexSettings.INDEX_SOFT_DELETES_SETTING.get(leaderIndexMetaData.getSettings()) == false) {
             listener.onFailure(new IllegalArgumentException("leader index [" + request.getLeaderIndex() +
                 "] does not have soft deletes enabled"));
             return;

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowAction.java

@@ -6,7 +6,6 @@
 
 package org.elasticsearch.xpack.ccr.action;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.master.AcknowledgedResponse;
@@ -214,9 +213,7 @@ static void validate(
                     "] as history uuid");
             }
         }
-        // soft deletes are enabled by default on indices created on 7.0.0 or later
-        if (leaderIndex.getSettings().getAsBoolean(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(),
-            IndexMetaData.SETTING_INDEX_VERSION_CREATED.get(leaderIndex.getSettings()).onOrAfter(Version.V_7_0_0)) == false) {
+        if (IndexSettings.INDEX_SOFT_DELETES_SETTING.get(leaderIndex.getSettings()) == false) {
             throw new IllegalArgumentException("leader index [" + leaderIndex.getIndex().getName() +
                 "] does not have soft deletes enabled");
         }