Add feature config to allow dropping views without purging (apache#2369)

* Add feature config to allow dropping views without purging

With tables, the client can decide whether to purge the table
on drop or not. However, Polaris Servers used to unconditionally
perform the purge on dropping a view.

After apache#1619 that behaviour effectively prevents dropping views
if the admin user does not set `DROP_WITH_PURGE_ENABLED`. The
latter, though, is not currently advisable per apache#1617.

This change introduces a new feature configuration
(`PURGE_VIEWS_ON_DROP`) that allows the admin user to instruct
Polaris servers to drop views without purging to achieve
operational parity with tables.

Fixes apache#2367

* review: rename to PURGE_VIEW_METADATA_ON_DROP

* review: re-fix description

Author: dimas-b

CHANGELOG.md

@@ -50,6 +50,8 @@ at locations that better optimize for object storage.
 - The Helm chart now supports Pod Disruption Budgets (PDBs) for Polaris components. This allows users to define
   the minimum number of pods that must be available during voluntary disruptions, such as node maintenance.
 
+- Feature configuration `PURGE_VIEW_METADATA_ON_DROP` was added to allow dropping views without purging their metadata files.
+
 ### Changes
 
 - Polaris Management API clients must be prepared to deal with new attributes in `AwsStorageConfigInfo` objects.

integration-tests/src/main/java/org/apache/polaris/service/it/test/PolarisRestCatalogIntegrationBase.java

@@ -1199,6 +1199,32 @@ public void testDropViewStatus() {
     }
   }
 
+  @Test
+  public void testDropViewWithPurge() {
+    restCatalog.createNamespace(Namespace.of("ns1"));
+    TableIdentifier id = TableIdentifier.of(Namespace.of("ns1"), "view1");
+    restCatalog
+        .buildView(id)
+        .withSchema(SCHEMA)
+        .withDefaultNamespace(Namespace.of("ns1"))
+        .withQuery("spark", VIEW_QUERY)
+        .create();
+
+    Catalog catalog = managementApi.getCatalog(currentCatalogName);
+    Map<String, String> catalogProps = new HashMap<>(catalog.getProperties().toMap());
+    catalogProps.put(FeatureConfiguration.DROP_WITH_PURGE_ENABLED.catalogConfig(), "false");
+    catalogProps.put(FeatureConfiguration.PURGE_VIEW_METADATA_ON_DROP.catalogConfig(), "true");
+    managementApi.updateCatalog(catalog, catalogProps);
+
+    assertThatThrownBy(() -> restCatalog.dropView(id)).isInstanceOf(ForbiddenException.class);
+
+    catalog = managementApi.getCatalog(currentCatalogName);
+    catalogProps.put(FeatureConfiguration.PURGE_VIEW_METADATA_ON_DROP.catalogConfig(), "false");
+    managementApi.updateCatalog(catalog, catalogProps);
+
+    assertThatCode(() -> restCatalog.dropView(id)).doesNotThrowAnyException();
+  }
+
   @Test
   public void testRenameViewStatus() {
     String tableName = "tbl1";

polaris-core/src/main/java/org/apache/polaris/core/config/FeatureConfiguration.java

@@ -191,6 +191,15 @@ public static void enforceFeatureEnabledOrThrow(
           .defaultValue(false)
           .buildFeatureConfiguration();
 
+  public static final FeatureConfiguration<Boolean> PURGE_VIEW_METADATA_ON_DROP =
+      PolarisConfiguration.<Boolean>builder()
+          .key("PURGE_VIEW_METADATA_ON_DROP")
+          .catalogConfig("polaris.config.purge-view-metadata-on-drop")
+          .description(
+              "If set to true, Polaris will attempt to delete view metadata files when a view is dropped.")
+          .defaultValue(true)
+          .buildFeatureConfiguration();
+
   public static final FeatureConfiguration<Integer> STORAGE_CREDENTIAL_DURATION_SECONDS =
       PolarisConfiguration.<Integer>builder()
           .key("STORAGE_CREDENTIAL_DURATION_SECONDS")

runtime/service/src/main/java/org/apache/polaris/service/catalog/iceberg/IcebergCatalog.java

@@ -801,7 +801,13 @@ protected ViewOperations newViewOps(TableIdentifier identifier) {
 
   @Override
   public boolean dropView(TableIdentifier identifier) {
-    return dropTableLike(PolarisEntitySubType.ICEBERG_VIEW, identifier, Map.of(), true).isSuccess();
+    boolean purge =
+        callContext
+            .getRealmConfig()
+            .getConfig(FeatureConfiguration.PURGE_VIEW_METADATA_ON_DROP, catalogEntity);
+
+    return dropTableLike(PolarisEntitySubType.ICEBERG_VIEW, identifier, Map.of(), purge)
+        .isSuccess();
   }
 
   @Override