improvements

python/delta/tables.py

@@ -594,14 +594,43 @@ def addFeatureSupport(self, featureName: str) -> None:
         DeltaTable._verify_type_str(featureName, "featureName")
         self._jdt.addFeatureSupport(featureName)
 
+    @since(3.4)  # type: ignore[arg-type]
+    def dropFeatureSupport(self, featureName: str, truncateHistory: Optional[bool] = None) -> None:
+        """
+        Modify the protocol to drop a supported feature. The operation always normalizes the
+        resulting protocol. Protocol normalization is the process of converting a table features
+        protocol to the weakest possible form. This primarily refers to converting a table features
+        protocol to a legacy protocol. A table features protocol can be represented with the legacy
+        representation only when the feature set of the former exactly matches a legacy protocol.
+        Normalization can also decrease the reader version of a table features protocol when it is
+        higher than necessary. For example:
+
+        (1, 7, None, {AppendOnly, Invariants, CheckConstraints}) -> (1, 3)
+        (3, 7, None, {RowTracking}) -> (1, 7, RowTracking)
+
+        The dropFeatureSupport method can be used as follows:
+        delta.tables.DeltaTable.dropFeatureSupport("rowTracking")
+
+        :param featureName: The name of the feature to drop.
+        :param truncateHistory: Optional value whether to truncate history. If not specified,
+                                the history is not truncated.
+        :return: None.
+        """
+        DeltaTable._verify_type_str(featureName, "featureName")
+        if truncateHistory is None:
+            self._jdt.dropFeatureSupport(featureName)
+        else:
+            DeltaTable._verify_type_bool(truncateHistory, "truncateHistory")
+            self._jdt.dropFeatureSupport(featureName, truncateHistory)
+
     @since(1.2)  # type: ignore[arg-type]
     def restoreToVersion(self, version: int) -> DataFrame:
         """
         Restore the DeltaTable to an older version of the table specified by version number.
 
         Example::
 
-            io.delta.tables.DeltaTable.restoreToVersion(1)
+            delta.tables.DeltaTable.restoreToVersion(1)
 
         :param version: target version of restored table
         :return: Dataframe with metrics of restore operation.
@@ -622,8 +651,8 @@ def restoreToTimestamp(self, timestamp: str) -> DataFrame:
 
         Example::
 
-            io.delta.tables.DeltaTable.restoreToTimestamp('2021-01-01')
-            io.delta.tables.DeltaTable.restoreToTimestamp('2021-01-01 01:01:01')
+            delta.tables.DeltaTable.restoreToTimestamp('2021-01-01')
+            delta.tables.DeltaTable.restoreToTimestamp('2021-01-01 01:01:01')
 
         :param timestamp: target timestamp of restored table
         :return: Dataframe with metrics of restore operation.
@@ -658,6 +687,11 @@ def optimize(self) -> "DeltaOptimizeBuilder":
         jbuilder = self._jdt.optimize()
         return DeltaOptimizeBuilder(self._spark, jbuilder)
 
+    @classmethod
+    def _verify_type_bool(self, variable, name):
+        if not isinstance(variable, bool) or variable is None:
+            raise ValueError("%s needs to be a boolean but got '%s'." % (name, type(variable)))
+
     @staticmethod  # type: ignore[arg-type]
     def _verify_type_str(variable: str, name: str) -> None:
         if not isinstance(variable, str) or variable is None:

python/delta/tests/test_deltatable.py

@@ -1151,16 +1151,19 @@ def test_delta_table_builder_with_bad_args(self) -> None:
         with self.assertRaises(TypeError):
             builder.property("1", 1)  # type: ignore[arg-type]
 
-    def test_protocolUpgrade(self) -> None:
+    def __create_df_for_feature_tests(self) -> DeltaTable:
         try:
-            self.spark.conf.set('spark.databricks.delta.minWriterVersion', '2')
             self.spark.conf.set('spark.databricks.delta.minReaderVersion', '1')
+            self.spark.conf.set('spark.databricks.delta.minWriterVersion', '2')
             self.__writeDeltaTable([('a', 1), ('b', 2), ('c', 3), ('d', 4)])
-            dt = DeltaTable.forPath(self.spark, self.tempFile)
-            dt.upgradeTableProtocol(1, 3)
+            return DeltaTable.forPath(self.spark, self.tempFile)
         finally:
-            self.spark.conf.unset('spark.databricks.delta.minWriterVersion')
             self.spark.conf.unset('spark.databricks.delta.minReaderVersion')
+            self.spark.conf.unset('spark.databricks.delta.minWriterVersion')
+
+    def test_protocolUpgrade(self) -> None:
+        dt = self.__create_df_for_feature_tests()
+        dt.upgradeTableProtocol(1, 3)
 
         # cannot downgrade once upgraded
         dt.upgradeTableProtocol(1, 2)
@@ -1189,14 +1192,7 @@ def test_protocolUpgrade(self) -> None:
             dt.upgradeTableProtocol(1, {})  # type: ignore[arg-type]
 
     def test_addFeatureSupport(self) -> None:
-        try:
-            self.spark.conf.set('spark.databricks.delta.minReaderVersion', '1')
-            self.spark.conf.set('spark.databricks.delta.minWriterVersion', '2')
-            self.__writeDeltaTable([('a', 1), ('b', 2), ('c', 3), ('d', 4)])
-            dt = DeltaTable.forPath(self.spark, self.tempFile)
-        finally:
-            self.spark.conf.unset('spark.databricks.delta.minReaderVersion')
-            self.spark.conf.unset('spark.databricks.delta.minWriterVersion')
+        dt = self.__create_df_for_feature_tests()
 
         # bad args
         with self.assertRaisesRegex(Py4JJavaError, "DELTA_UNSUPPORTED_FEATURES_IN_CONFIG"):
@@ -1224,6 +1220,69 @@ def test_addFeatureSupport(self) -> None:
         self.assertEqual(sorted(dt_details["tableFeatures"]),
                          ["appendOnly", "deletionVectors", "invariants"])
 
+    def test_dropFeatureSupport(self) -> None:
+        dt = self.__create_df_for_feature_tests()
+
+        dt.addFeatureSupport("testRemovableWriter")
+        dt_details = dt.detail().collect()[0].asDict()
+        self.assertTrue(dt_details["minReaderVersion"] == 1)
+        self.assertTrue(dt_details["minWriterVersion"] == 7, "Should upgrade to table features")
+        self.assertEqual(sorted(dt_details["tableFeatures"]),
+                         ["appendOnly", "invariants", "testRemovableWriter"])
+
+        # Attempt truncating the history when dropping a feature that is not required.
+        # This verifies the truncateHistory option was correctly passed.
+        with self.assertRaisesRegex(Exception,
+                                    "DELTA_FEATURE_DROP_HISTORY_TRUNCATION_NOT_ALLOWED"):
+            dt.dropFeatureSupport("testRemovableWriter", True)
+
+        dt.dropFeatureSupport("testRemovableWriter")
+        dt_details = dt.detail().collect()[0].asDict()
+        self.assertTrue(dt_details["minReaderVersion"] == 1)
+        self.assertTrue(dt_details["minWriterVersion"] == 2, "Should return to legacy protocol")
+
+        dt.addFeatureSupport("testRemovableReaderWriter")
+        dt_details = dt.detail().collect()[0].asDict()
+        self.assertTrue(dt_details["minReaderVersion"] == 3, "Should upgrade to table features")
+        self.assertTrue(dt_details["minWriterVersion"] == 7, "Should upgrade to table features")
+        self.assertEqual(sorted(dt_details["tableFeatures"]),
+                         ["appendOnly", "invariants", "testRemovableReaderWriter"])
+
+        dt.dropFeatureSupport("testRemovableReaderWriter")
+        dt_details = dt.detail().collect()[0].asDict()
+        self.assertTrue(dt_details["minReaderVersion"] == 1, "Should return to legacy protocol")
+        self.assertTrue(dt_details["minWriterVersion"] == 2, "Should return to legacy protocol")
+
+        # Try to drop an unsupported feature.
+        with self.assertRaisesRegex(Exception, "DELTA_FEATURE_DROP_UNSUPPORTED_CLIENT_FEATURE"):
+            dt.dropFeatureSupport("__invalid_feature__")
+
+        # Try to drop a feature that is not present in the protocol.
+        with self.assertRaisesRegex(Exception, "DELTA_FEATURE_DROP_FEATURE_NOT_PRESENT"):
+            dt.dropFeatureSupport("testRemovableReaderWriter")
+
+        # Try to drop a non-removable feature.
+        with self.assertRaisesRegex(Exception, "DELTA_FEATURE_DROP_NONREMOVABLE_FEATURE"):
+            dt.dropFeatureSupport("testReaderWriter")
+
+        with self.assertRaisesRegex(ValueError, "featureName needs to be a string"):
+            dt.dropFeatureSupport(12345)  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "featureName needs to be a string"):
+            dt.dropFeatureSupport([12345])  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "featureName needs to be a string"):
+            dt.dropFeatureSupport({})  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "featureName needs to be a string"):
+            dt.dropFeatureSupport([])  # type: ignore[arg-type]
+
+        with self.assertRaisesRegex(ValueError, "truncateHistory needs to be a boolean"):
+            dt.dropFeatureSupport("testRemovableWriter", 12345)  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "truncateHistory needs to be a boolean"):
+            dt.dropFeatureSupport("testRemovableWriter", [12345])  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "truncateHistory needs to be a boolean"):
+            dt.dropFeatureSupport("testRemovableWriter", {})  # type: ignore[arg-type]
+        with self.assertRaisesRegex(ValueError, "truncateHistory needs to be a boolean"):
+            dt.dropFeatureSupport("testRemovableWriter", [])  # type: ignore[arg-type]
+
     def test_restore_to_version(self) -> None:
         self.__writeDeltaTable([('a', 1), ('b', 2)])
         self.__overwriteDeltaTable([('a', 3), ('b', 2)],

spark/src/main/scala/io/delta/tables/DeltaTable.scala

@@ -20,9 +20,9 @@ import scala.collection.JavaConverters._
 
 import org.apache.spark.sql.delta._
 import org.apache.spark.sql.delta.DeltaTableUtils.withActiveSession
-import org.apache.spark.sql.delta.actions.{Protocol, TableFeatureProtocolUtils}
+import org.apache.spark.sql.delta.actions.TableFeatureProtocolUtils
 import org.apache.spark.sql.delta.catalog.DeltaTableV2
-import org.apache.spark.sql.delta.commands.AlterTableSetPropertiesDeltaCommand
+import org.apache.spark.sql.delta.commands.{AlterTableDropFeatureDeltaCommand, AlterTableSetPropertiesDeltaCommand}
 import org.apache.spark.sql.delta.sources.DeltaSQLConf
 import io.delta.tables.execution._
 import org.apache.hadoop.fs.Path
@@ -562,6 +562,73 @@ class DeltaTable private[tables](
     toDataset(sparkSession, alterTableCmd)
   }
 
+  private def executeDropFeature(featureName: String, truncateHistory: Option[Boolean]): Unit = {
+    val alterTableCmd = AlterTableDropFeatureDeltaCommand(
+      table = table,
+      featureName = featureName,
+      truncateHistory = truncateHistory.getOrElse(false))
+    toDataset(sparkSession, alterTableCmd)
+  }
+
+  /**
+   * Modify the protocol to drop a supported feature. The operation always normalizes the
+   * resulting protocol. Protocol normalization is the process of converting a table features
+   * protocol to the weakest possible form. This primarily refers to converting a table features
+   * protocol to a legacy protocol. A table features protocol can be represented with the legacy
+   * representation only when the feature set of the former exactly matches a legacy protocol.
+   * Normalization can also decrease the reader version of a table features protocol when it is
+   * higher than necessary. For example:
+   *
+   * (1, 7, None, {AppendOnly, Invariants, CheckConstraints}) -> (1, 3)
+   * (3, 7, None, {RowTracking}) -> (1, 7, RowTracking)
+   *
+   * The dropFeatureSupport method can be used as follows:
+   * {{{
+   *   io.delta.tables.DeltaTable.dropFeatureSupport("rowTracking")
+   * }}}
+   *
+   * See online documentation for more details.
+   *
+   * @param featureName The name of the feature to drop.
+   * @param truncateHistory Whether to truncate history before downgrading the protocol.
+   * @return None.
+   * @since 3.4.0
+   */
+  def dropFeatureSupport(
+      featureName: String,
+      truncateHistory: Boolean): Unit = withActiveSession(sparkSession) {
+    executeDropFeature(featureName, Some(truncateHistory))
+  }
+
+  /**
+   * Modify the protocol to drop a supported feature. The operation always normalizes the
+   * resulting protocol. Protocol normalization is the process of converting a table features
+   * protocol to the weakest possible form. This primarily refers to converting a table features
+   * protocol to a legacy protocol. A table features protocol can be represented with the legacy
+   * representation only when the feature set of the former exactly matches a legacy protocol.
+   * Normalization can also decrease the reader version of a table features protocol when it is
+   * higher than necessary. For example:
+   *
+   * (1, 7, None, {AppendOnly, Invariants, CheckConstraints}) -> (1, 3)
+   * (3, 7, None, {RowTracking}) -> (1, 7, RowTracking)
+   *
+   * The dropFeatureSupport method can be used as follows:
+   * {{{
+   *   io.delta.tables.DeltaTable.dropFeatureSupport("rowTracking")
+   * }}}
+   *
+   * Note, this command will not truncate history.
+   *
+   * See online documentation for more details.
+   *
+   * @param featureName The name of the feature to drop.
+   * @return None.
+   * @since 3.4.0
+   */
+  def dropFeatureSupport(featureName: String): Unit = withActiveSession(sparkSession) {
+    executeDropFeature(featureName, None)
+  }
+
   /**
    * Clone a DeltaTable to a given destination to mirror the existing table's data and metadata.
    *

spark/src/main/scala/org/apache/spark/sql/delta/TableFeature.scala

@@ -1044,7 +1044,7 @@ object TestReaderWriterMetadataAutoUpdateFeature
   }
 }
 
-private[sql] object TestRemovableWriterFeature
+object TestRemovableWriterFeature
   extends WriterFeature(name = "testRemovableWriter")
   with FeatureAutomaticallyEnabledByMetadata
   with RemovableFeature {
@@ -1093,7 +1093,7 @@ private[sql] object TestRemovableWriterFeatureWithDependency
     Set(TestRemovableReaderWriterFeature, TestRemovableWriterFeature)
 }
 
-private[sql] object TestRemovableReaderWriterFeature
+object TestRemovableReaderWriterFeature
   extends ReaderWriterFeature(name = "testRemovableReaderWriter")
     with FeatureAutomaticallyEnabledByMetadata
     with RemovableFeature {

spark/src/main/scala/org/apache/spark/sql/delta/commands/alterDeltaTableCommands.scala

@@ -322,7 +322,7 @@ case class AlterTableDropFeatureDeltaCommand(
     // Check whether the protocol contains the feature in either the writer features list or
     // the reader+writer features list. Note, protocol needs to denormalized to allow dropping
     // features from legacy protocols.
-    val protocol = table.initialSnapshot.protocol
+    val protocol = table.deltaLog.update().protocol
     val protocolContainsFeatureName =
       protocol.implicitlyAndExplicitlySupportedFeatures.map(_.name).contains(featureName)
     if (!protocolContainsFeatureName) {

spark/src/test/scala/io/delta/tables/DeltaTableSuite.scala

@@ -22,7 +22,7 @@ import java.util.Locale
 import scala.language.postfixOps
 
 // scalastyle:off import.ordering.noEmptyLine
-import org.apache.spark.sql.delta.{AppendOnlyTableFeature, DeltaIllegalArgumentException, DeltaLog, DeltaTableFeatureException, FakeFileSystem, InvariantsTableFeature, TestReaderWriterFeature, TestWriterFeature}
+import org.apache.spark.sql.delta.{AppendOnlyTableFeature, DeltaIllegalArgumentException, DeltaLog, DeltaTableFeatureException, FakeFileSystem, InvariantsTableFeature, TestReaderWriterFeature, TestRemovableReaderWriterFeature, TestRemovableWriterFeature, TestWriterFeature}
 import org.apache.spark.sql.delta.actions.{ Metadata, Protocol }
 import org.apache.spark.sql.delta.storage.LocalLogStore
 import org.apache.spark.sql.delta.test.DeltaSQLCommandTest
@@ -247,6 +247,7 @@ class DeltaTableHadoopOptionsSuite extends QueryTest
     "cloneAtVersion",
     "delete",
     "detail",
+    "dropFeatureSupport",
     "generate",
     "history",
     "merge",
@@ -631,8 +632,7 @@ class DeltaTableHadoopOptionsSuite extends QueryTest
     }
   }
 
-  test(
-    "addFeatureSupport - with filesystem options.") {
+  test("addFeatureSupport - with filesystem options.") {
     withTempDir { dir =>
       val path = fakeFileSystemPath(dir)
       val fsOptions = fakeFileSystemOptions
@@ -670,6 +670,70 @@ class DeltaTableHadoopOptionsSuite extends QueryTest
     }
   }
 
+  test("dropFeatureSupport - with filesystem options.") {
+    withTempDir { dir =>
+      val path = fakeFileSystemPath(dir)
+      val fsOptions = fakeFileSystemOptions
+
+      // create a table with a default Protocol.
+      val testSchema = spark.range(1).schema
+      val log = DeltaLog.forTable(spark, new Path(path), fsOptions)
+      log.createLogDirectoriesIfNotExists()
+      log.store.write(
+        FileNames.unsafeDeltaFile(log.logPath, 0),
+        Iterator(Metadata(schemaString = testSchema.json).json, Protocol(1, 2).json),
+        overwrite = false,
+        log.newDeltaHadoopConf())
+      log.update()
+
+      // update the protocol to support a writer feature.
+      val table = DeltaTable.forPath(spark, path, fsOptions)
+      table.addFeatureSupport(TestRemovableWriterFeature.name)
+      assert(log.update().protocol === Protocol(1, 7).withFeatures(Seq(
+        AppendOnlyTableFeature,
+        InvariantsTableFeature,
+        TestRemovableWriterFeature)))
+
+      // Attempt truncating the history when dropping a feature that is not required.
+      // This verifies the truncateHistory option was correctly passed.
+      assert(intercept[DeltaTableFeatureException] {
+        table.dropFeatureSupport("testRemovableWriter", truncateHistory = true)
+      }.getErrorClass === "DELTA_FEATURE_DROP_HISTORY_TRUNCATION_NOT_ALLOWED")
+
+      // Drop feature.
+      table.dropFeatureSupport(TestRemovableWriterFeature.name)
+      // After dropping the feature we should return back to the original protocol.
+      assert(log.update().protocol === Protocol(1, 2))
+
+      table.addFeatureSupport(TestRemovableReaderWriterFeature.name)
+      assert(
+        log.update().protocol === Protocol(3, 7).withFeatures(Seq(
+          AppendOnlyTableFeature,
+          InvariantsTableFeature,
+          TestRemovableReaderWriterFeature)))
+
+      // Drop feature.
+      table.dropFeatureSupport(TestRemovableReaderWriterFeature.name)
+      // After dropping the feature we should return back to the original protocol.
+      assert(log.update().protocol === Protocol(1, 2))
+
+      // Try to drop an unsupported feature.
+      assert(intercept[DeltaTableFeatureException] {
+        table.dropFeatureSupport("__invalid_feature__")
+      }.getErrorClass === "DELTA_FEATURE_DROP_UNSUPPORTED_CLIENT_FEATURE")
+
+      // Try to drop a feature that is not present in the protocol.
+      assert(intercept[DeltaTableFeatureException] {
+        table.dropFeatureSupport(TestRemovableReaderWriterFeature.name)
+      }.getErrorClass === "DELTA_FEATURE_DROP_FEATURE_NOT_PRESENT")
+
+      // Try to drop a non-removable feature.
+      assert(intercept[DeltaTableFeatureException] {
+        table.dropFeatureSupport(TestReaderWriterFeature.name)
+      }.getErrorClass === "DELTA_FEATURE_DROP_NONREMOVABLE_FEATURE")
+    }
+  }
+
   test("details - with filesystem options.") {
     withTempDir{ dir =>
       val path = fakeFileSystemPath(dir)