Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/729#discussion_r100676978
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/statistics/StatisticsAggBatch.java
---
@@ -0,0 +1,256 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.drill.exec.physical.impl.statistics;
+
+import com.google.common.collect.Lists;
+import com.sun.codemodel.JExpr;
+import org.apache.drill.common.expression.ErrorCollector;
+import org.apache.drill.common.expression.ErrorCollectorImpl;
+import org.apache.drill.common.expression.FunctionCallFactory;
+import org.apache.drill.common.expression.LogicalExpression;
+import org.apache.drill.common.expression.SchemaPath;
+import org.apache.drill.common.expression.ValueExpressions;
+import org.apache.drill.exec.exception.ClassTransformationException;
+import org.apache.drill.exec.exception.OutOfMemoryException;
+import org.apache.drill.exec.exception.SchemaChangeException;
+import org.apache.drill.exec.expr.ClassGenerator;
+import org.apache.drill.exec.expr.CodeGenerator;
+import org.apache.drill.exec.expr.ExpressionTreeMaterializer;
+import org.apache.drill.exec.expr.TypeHelper;
+import org.apache.drill.exec.expr.ValueVectorWriteExpression;
+import org.apache.drill.exec.ops.FragmentContext;
+import org.apache.drill.exec.physical.config.StatisticsAggregate;
+import org.apache.drill.exec.physical.impl.aggregate.StreamingAggBatch;
+import org.apache.drill.exec.physical.impl.aggregate.StreamingAggTemplate;
+import org.apache.drill.exec.physical.impl.aggregate.StreamingAggregator;
+import org.apache.drill.exec.planner.physical.StatsAggPrel.OperatorPhase;
+import org.apache.drill.exec.record.BatchSchema.SelectionVectorMode;
+import org.apache.drill.exec.record.MaterializedField;
+import org.apache.drill.exec.record.RecordBatch;
+import org.apache.drill.exec.record.TypedFieldId;
+import org.apache.drill.exec.store.ImplicitColumnExplorer;
+import org.apache.drill.exec.vector.ValueVector;
+import org.apache.drill.exec.vector.complex.FieldIdUtil;
+import org.apache.drill.exec.vector.complex.MapVector;
+
+import java.io.IOException;
+import java.util.GregorianCalendar;
+import java.util.List;
+import java.util.TimeZone;
+
+/**
+ * TODO: This needs cleanup. Currently the key values are constants and we
compare the constants
+ * for every record. Seems unnecessary.
+ *
+ * Example input and output:
+ * Schema of incoming batch: region_id (VARCHAR), sales_city (VARCHAR),
cnt (BIGINT)
+ * Schema of output:
+ * "schema" : BIGINT - Schema number. For each schema change this
number is incremented.
+ * "computed" : BIGINT - What time is it computed?
+ * "columns" : MAP - Column names
--- End diff --
Maps are key/value collections. (A map in Drill is really a nested record
or tuple.)
Should I infer that the map contains column names as keys, types as a
values? How are types encoded? The name associated with the type in MinorType?
Or, do we also include the additional MajorType info such as
Required/Nullable/Repeated? For decimals, do we also track precision, etc?
For names, if the name is nested, is this the full path name "a.b"? Are
names case sensitive?
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