diff --git a/client/rest-high-level/src/main/java/org/elasticsearch/client/dataframe/transforms/pivot/SingleGroupSource.java b/client/rest-high-level/src/main/java/org/elasticsearch/client/dataframe/transforms/pivot/SingleGroupSource.java
index 8168d8850e7..b1234277d8c 100644
--- a/client/rest-high-level/src/main/java/org/elasticsearch/client/dataframe/transforms/pivot/SingleGroupSource.java
+++ b/client/rest-high-level/src/main/java/org/elasticsearch/client/dataframe/transforms/pivot/SingleGroupSource.java
@@ -30,32 +30,9 @@ public abstract class SingleGroupSource implements ToXContentObject {
     protected static final ParseField FIELD = new ParseField("field");
 
     public enum Type {
-        TERMS(0),
-        HISTOGRAM(1),
-        DATE_HISTOGRAM(2);
-
-        private final byte id;
-
-        Type(int id) {
-            this.id = (byte) id;
-        }
-
-        public byte getId() {
-            return id;
-        }
-
-        public static Type fromId(byte id) {
-            switch (id) {
-                case 0:
-                    return TERMS;
-                case 1:
-                    return HISTOGRAM;
-                case 2:
-                    return DATE_HISTOGRAM;
-                default:
-                    throw new IllegalArgumentException("unknown type");
-            }
-        }
+        TERMS,
+        HISTOGRAM,
+        DATE_HISTOGRAM;
 
         public String value() {
             return name().toLowerCase(Locale.ROOT);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/DataFrameTransformConfig.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/DataFrameTransformConfig.java
index a8e14faf2f0..89eab5605ca 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/DataFrameTransformConfig.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/DataFrameTransformConfig.java
@@ -215,7 +215,7 @@ public class DataFrameTransformConfig extends AbstractDiffable<DataFrameTransfor
     }
 
     public static DataFrameTransformConfig fromXContent(final XContentParser parser, @Nullable final String optionalTransformId,
-            boolean lenient) throws IOException {
+            boolean lenient) {
 
         return lenient ? LENIENT_PARSER.apply(parser, optionalTransformId) : STRICT_PARSER.apply(parser, optionalTransformId);
     }
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/DateHistogramGroupSource.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/DateHistogramGroupSource.java
index a60a7ef98e9..f4bf094235a 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/DateHistogramGroupSource.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/DateHistogramGroupSource.java
@@ -20,7 +20,7 @@ import java.time.ZoneOffset;
 import java.util.Objects;
 
 
-public class DateHistogramGroupSource extends SingleGroupSource<DateHistogramGroupSource> {
+public class DateHistogramGroupSource extends SingleGroupSource {
 
     private static final String NAME = "data_frame_date_histogram_group";
     private static final ParseField TIME_ZONE = new ParseField("time_zone");
@@ -51,7 +51,7 @@ public class DateHistogramGroupSource extends SingleGroupSource<DateHistogramGro
             return new DateHistogramGroupSource(field);
         });
 
-        declareValuesSourceFields(parser, null);
+        declareValuesSourceFields(parser);
 
         parser.declareField((histogram, interval) -> {
             if (interval instanceof Long) {
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfig.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfig.java
index de394fa3f19..e5ba14c381a 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfig.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfig.java
@@ -40,9 +40,9 @@ public class GroupConfig implements Writeable, ToXContentObject {
     private static final Logger logger = LogManager.getLogger(GroupConfig.class);
 
     private final Map<String, Object> source;
-    private final Map<String, SingleGroupSource<?>> groups;
+    private final Map<String, SingleGroupSource> groups;
 
-    public GroupConfig(final Map<String, Object> source, final Map<String, SingleGroupSource<?>> groups) {
+    public GroupConfig(final Map<String, Object> source, final Map<String, SingleGroupSource> groups) {
         this.source = ExceptionsHelper.requireNonNull(source, DataFrameField.GROUP_BY.getPreferredName());
         this.groups = groups;
     }
@@ -64,7 +64,7 @@ public class GroupConfig implements Writeable, ToXContentObject {
         });
     }
 
-    public Map <String, SingleGroupSource<?>> getGroups() {
+    public Map <String, SingleGroupSource> getGroups() {
         return groups;
     }
 
@@ -109,7 +109,7 @@ public class GroupConfig implements Writeable, ToXContentObject {
     public static GroupConfig fromXContent(final XContentParser parser, boolean lenient) throws IOException {
         NamedXContentRegistry registry = parser.getXContentRegistry();
         Map<String, Object> source = parser.mapOrdered();
-        Map<String, SingleGroupSource<?>> groups = null;
+        Map<String, SingleGroupSource> groups = null;
 
         if (source.isEmpty()) {
             if (lenient) {
@@ -133,9 +133,9 @@ public class GroupConfig implements Writeable, ToXContentObject {
         return new GroupConfig(source, groups);
     }
 
-    private static Map<String, SingleGroupSource<?>> parseGroupConfig(final XContentParser parser,
+    private static Map<String, SingleGroupSource> parseGroupConfig(final XContentParser parser,
             boolean lenient) throws IOException {
-        LinkedHashMap<String, SingleGroupSource<?>> groups = new LinkedHashMap<>();
+        LinkedHashMap<String, SingleGroupSource> groups = new LinkedHashMap<>();
 
         // be parsing friendly, whether the token needs to be advanced or not (similar to what ObjectParser does)
         XContentParser.Token token;
@@ -158,7 +158,7 @@ public class GroupConfig implements Writeable, ToXContentObject {
 
             token = parser.nextToken();
             ensureExpectedToken(XContentParser.Token.START_OBJECT, token, parser::getTokenLocation);
-            SingleGroupSource<?> groupSource;
+            SingleGroupSource groupSource;
             switch (groupType) {
             case TERMS:
                 groupSource = TermsGroupSource.fromXContent(parser, lenient);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/HistogramGroupSource.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/HistogramGroupSource.java
index 95e1068e0f4..737590a0cc1 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/HistogramGroupSource.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/HistogramGroupSource.java
@@ -17,7 +17,7 @@ import java.util.Objects;
 
 import static org.elasticsearch.common.xcontent.ConstructingObjectParser.optionalConstructorArg;
 
-public class HistogramGroupSource extends SingleGroupSource<HistogramGroupSource> {
+public class HistogramGroupSource extends SingleGroupSource {
 
     static final ParseField INTERVAL = new ParseField("interval");
     private static final String NAME = "data_frame_histogram_group";
@@ -44,7 +44,7 @@ public class HistogramGroupSource extends SingleGroupSource<HistogramGroupSource
             double interval = (double) args[1];
             return new HistogramGroupSource(field, interval);
         });
-        declareValuesSourceFields(parser, null);
+        declareValuesSourceFields(parser);
         parser.declareDouble(optionalConstructorArg(), INTERVAL);
         return parser;
     }
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/PivotConfig.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/PivotConfig.java
index 4eef08bd9c0..993ba78482a 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/PivotConfig.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/PivotConfig.java
@@ -91,7 +91,7 @@ public class PivotConfig implements Writeable, ToXContentObject {
         builder.field(CompositeAggregationBuilder.SOURCES_FIELD_NAME.getPreferredName());
         builder.startArray();
 
-        for (Entry<String, SingleGroupSource<?>> groupBy : groups.getGroups().entrySet()) {
+        for (Entry<String, SingleGroupSource> groupBy : groups.getGroups().entrySet()) {
             builder.startObject();
             builder.startObject(groupBy.getKey());
             builder.field(groupBy.getValue().getType().value(), groupBy.getValue());
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/SingleGroupSource.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/SingleGroupSource.java
index 8ba5caddb6f..0cdef0e4c3a 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/SingleGroupSource.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/SingleGroupSource.java
@@ -13,7 +13,6 @@ import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.xcontent.AbstractObjectParser;
 import org.elasticsearch.common.xcontent.ToXContentObject;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.support.ValueType;
 
 import java.io.IOException;
 import java.util.Locale;
@@ -24,7 +23,7 @@ import static org.elasticsearch.common.xcontent.ConstructingObjectParser.optiona
 /*
  * Base class for a single source for group_by
  */
-public abstract class SingleGroupSource<AB extends SingleGroupSource<AB>> implements Writeable, ToXContentObject {
+public abstract class SingleGroupSource implements Writeable, ToXContentObject {
 
     public enum Type {
         TERMS(0),
@@ -64,8 +63,7 @@ public abstract class SingleGroupSource<AB extends SingleGroupSource<AB>> implem
     // TODO: add script
     protected final String field;
 
-    static <VB extends SingleGroupSource<?>, T> void declareValuesSourceFields(AbstractObjectParser<VB, T> parser,
-            ValueType targetValueType) {
+    static <T> void declareValuesSourceFields(AbstractObjectParser<? extends SingleGroupSource, T> parser) {
         // either script or field
         parser.declareString(optionalConstructorArg(), FIELD);
     }
@@ -109,7 +107,7 @@ public abstract class SingleGroupSource<AB extends SingleGroupSource<AB>> implem
             return false;
         }
 
-        final SingleGroupSource<?> that = (SingleGroupSource<?>) other;
+        final SingleGroupSource that = (SingleGroupSource) other;
 
         return Objects.equals(this.field, that.field);
     }
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/TermsGroupSource.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/TermsGroupSource.java
index 8c18e43be07..d4585a611b3 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/TermsGroupSource.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/TermsGroupSource.java
@@ -15,7 +15,7 @@ import java.io.IOException;
 /*
  * A terms aggregation source for group_by
  */
-public class TermsGroupSource extends SingleGroupSource<TermsGroupSource> {
+public class TermsGroupSource extends SingleGroupSource {
     private static final String NAME = "data_frame_terms_group";
 
     private static final ConstructingObjectParser<TermsGroupSource, Void> STRICT_PARSER = createParser(false);
@@ -27,7 +27,7 @@ public class TermsGroupSource extends SingleGroupSource<TermsGroupSource> {
             return new TermsGroupSource(field);
         });
 
-        SingleGroupSource.declareValuesSourceFields(parser, null);
+        SingleGroupSource.declareValuesSourceFields(parser);
         return parser;
     }
 
diff --git a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfigTests.java b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfigTests.java
index e503d887cf3..f7b95525842 100644
--- a/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfigTests.java
+++ b/x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/dataframe/transforms/pivot/GroupConfigTests.java
@@ -29,14 +29,14 @@ public class GroupConfigTests extends AbstractSerializingTestCase<GroupConfig> {
 
     public static GroupConfig randomGroupConfig() {
         Map<String, Object> source = new LinkedHashMap<>();
-        Map<String, SingleGroupSource<?>> groups = new LinkedHashMap<>();
+        Map<String, SingleGroupSource> groups = new LinkedHashMap<>();
 
         // ensure that the unlikely does not happen: 2 group_by's share the same name
         Set<String> names = new HashSet<>();
         for (int i = 0; i < randomIntBetween(1, 20); ++i) {
             String targetFieldName = randomAlphaOfLengthBetween(1, 20);
             if (names.add(targetFieldName)) {
-                SingleGroupSource<?> groupBy;
+                SingleGroupSource groupBy;
                 Type type = randomFrom(SingleGroupSource.Type.values());
                 switch (type) {
                 case TERMS:
@@ -88,7 +88,7 @@ public class GroupConfigTests extends AbstractSerializingTestCase<GroupConfig> {
         }
     }
 
-    private static Map<String, Object> getSource(SingleGroupSource<?> groupSource) {
+    private static Map<String, Object> getSource(SingleGroupSource groupSource) {
         try (XContentBuilder xContentBuilder = XContentFactory.jsonBuilder()) {
             XContentBuilder content = groupSource.toXContent(xContentBuilder, ToXContent.EMPTY_PARAMS);
             return XContentHelper.convertToMap(BytesReference.bytes(content), true, XContentType.JSON).v2();
diff --git a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportGetDataFrameTransformsAction.java b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportGetDataFrameTransformsAction.java
index bbdd8a6dee8..00bc15b1db6 100644
--- a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportGetDataFrameTransformsAction.java
+++ b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportGetDataFrameTransformsAction.java
@@ -28,8 +28,6 @@ import org.elasticsearch.xpack.core.dataframe.action.GetDataFrameTransformsActio
 import org.elasticsearch.xpack.core.dataframe.transforms.DataFrameTransformConfig;
 import org.elasticsearch.xpack.dataframe.persistence.DataFrameInternalIndex;
 
-import java.io.IOException;
-
 import static org.elasticsearch.xpack.core.dataframe.DataFrameField.INDEX_DOC_TYPE;
 
 
@@ -62,7 +60,7 @@ public class TransportGetDataFrameTransformsAction extends AbstractTransportGetR
     }
 
     @Override
-    protected DataFrameTransformConfig parse(XContentParser parser) throws IOException {
+    protected DataFrameTransformConfig parse(XContentParser parser) {
         return DataFrameTransformConfig.fromXContent(parser, null, true);
     }
 
diff --git a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportPreviewDataFrameTransformAction.java b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportPreviewDataFrameTransformAction.java
index b65830f72e7..b5642310df3 100644
--- a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportPreviewDataFrameTransformAction.java
+++ b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/action/TransportPreviewDataFrameTransformAction.java
@@ -85,9 +85,8 @@ public class TransportPreviewDataFrameTransformAction extends
                             DataFrameIndexerTransformStats stats = DataFrameIndexerTransformStats.withDefaultTransformId();
                             // remove all internal fields
                             List<Map<String, Object>> results = pivot.extractResults(agg, deducedMappings, stats)
-                                    .map(record -> {
+                                    .peek(record -> {
                                         record.keySet().removeIf(k -> k.startsWith("_"));
-                                        return record;
                                     }).collect(Collectors.toList());
                             listener.onResponse(results);
                         },
diff --git a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/checkpoint/CheckpointException.java b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/checkpoint/CheckpointException.java
index 0a0a50761f0..f8405d37057 100644
--- a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/checkpoint/CheckpointException.java
+++ b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/checkpoint/CheckpointException.java
@@ -7,20 +7,13 @@
 package org.elasticsearch.xpack.dataframe.checkpoint;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.common.io.stream.StreamInput;
 
-import java.io.IOException;
-
-public class CheckpointException extends ElasticsearchException {
-    public CheckpointException(String msg, Object... params) {
+class CheckpointException extends ElasticsearchException {
+    CheckpointException(String msg, Object... params) {
         super(msg, null, params);
     }
 
-    public CheckpointException(String msg, Throwable cause, Object... params) {
+    CheckpointException(String msg, Throwable cause, Object... params) {
         super(msg, cause, params);
     }
-
-    public CheckpointException(StreamInput in) throws IOException {
-        super(in);
-    }
 }
diff --git a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/DataFrameTransformTask.java b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/DataFrameTransformTask.java
index 4088863a895..b8ceb2e7bd4 100644
--- a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/DataFrameTransformTask.java
+++ b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/DataFrameTransformTask.java
@@ -240,7 +240,7 @@ public class DataFrameTransformTask extends AllocatedPersistentTask implements S
     public synchronized void triggered(Event event) {
         //  for now no rerun, so only trigger if checkpoint == 0
         if (currentCheckpoint.get() == 0 && event.getJobName().equals(SCHEDULE_NAME + "_" + transform.getId())) {
-            logger.debug("Data frame indexer [" + event.getJobName() + "] schedule has triggered, state: [" + indexer.getState() + "]");
+            logger.debug("Data frame indexer [{}] schedule has triggered, state: [{}]", event.getJobName(), indexer.getState());
             indexer.maybeTriggerAsyncJob(System.currentTimeMillis());
         }
     }
@@ -336,7 +336,7 @@ public class DataFrameTransformTask extends AllocatedPersistentTask implements S
         @Override
         public synchronized boolean maybeTriggerAsyncJob(long now) {
             if (taskState.get() == DataFrameTransformTaskState.FAILED) {
-                logger.debug("Schedule was triggered for transform [" + getJobId() + "] but task is failed.  Ignoring trigger.");
+                logger.debug("Schedule was triggered for transform [{}] but task is failed. Ignoring trigger.", getJobId());
                 return false;
             }
 
diff --git a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/pivot/SchemaUtil.java b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/pivot/SchemaUtil.java
index deb4afdb73d..95798e4c564 100644
--- a/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/pivot/SchemaUtil.java
+++ b/x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/transforms/pivot/SchemaUtil.java
@@ -133,10 +133,11 @@ public final class SchemaUtil {
             String sourceMapping = sourceFieldName == null ? null : sourceMappings.get(sourceFieldName);
             String destinationMapping = Aggregations.resolveTargetMapping(aggregationName, sourceMapping);
 
-            logger.debug(
-                    "Deduced mapping for: [" + targetFieldName + "], agg type [" + aggregationName + "] to [" + destinationMapping + "]");
+            logger.debug("Deduced mapping for: [{}], agg type [{}] to [{}]",
+                    targetFieldName, aggregationName, destinationMapping);
+
             if (Aggregations.isDynamicMapping(destinationMapping)) {
-                logger.info("Dynamic target mapping set for field ["+ targetFieldName +"] and aggregation [" + aggregationName +"]");
+                logger.debug("Dynamic target mapping set for field [{}] and aggregation [{}]", targetFieldName, aggregationName);
             } else if (destinationMapping != null) {
                 targetMapping.put(targetFieldName, destinationMapping);
             } else {
@@ -146,8 +147,7 @@ public final class SchemaUtil {
 
         fieldNamesForGrouping.forEach((targetFieldName, sourceFieldName) -> {
             String destinationMapping = sourceMappings.get(sourceFieldName);
-            logger.debug(
-                    "Deduced mapping for: [" + targetFieldName + "] to [" + destinationMapping + "]");
+            logger.debug("Deduced mapping for: [{}] to [{}]", targetFieldName, destinationMapping);
             if (destinationMapping != null) {
                 targetMapping.put(targetFieldName, destinationMapping);
             } else {
@@ -187,7 +187,9 @@ public final class SchemaUtil {
                             final Map<?, ?> map = (Map<?, ?>) typeMap;
                             if (map.containsKey("type")) {
                                 String type = map.get("type").toString();
-                                logger.debug("Extracted type for [" + fieldName + "] : [" + type + "] from index [" + indexName +"]");
+                                if (logger.isTraceEnabled()) {
+                                    logger.trace("Extracted type for [" + fieldName + "] : [" + type + "] from index [" + indexName + "]");
+                                }
                                 // TODO: overwrites types, requires resolve if
                                 // types are mixed
                                 extractedTypes.put(fieldName, type);