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https://issues.apache.org/jira/browse/DRILL-4081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15006145#comment-15006145
]
ASF GitHub Bot commented on DRILL-4081:
---------------------------------------
Github user jacques-n commented on a diff in the pull request:
https://github.com/apache/drill/pull/257#discussion_r44883499
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/record/SchemaUtil.java ---
@@ -0,0 +1,159 @@
+/**
+ * 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.record;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import org.apache.drill.common.expression.SchemaPath;
+import org.apache.drill.common.types.TypeProtos.DataMode;
+import org.apache.drill.common.types.TypeProtos.MajorType;
+import org.apache.drill.common.types.TypeProtos.MinorType;
+import org.apache.drill.common.types.Types;
+import org.apache.drill.exec.expr.TypeHelper;
+import org.apache.drill.exec.memory.BufferAllocator;
+import org.apache.drill.exec.ops.OperatorContext;
+import org.apache.drill.exec.physical.impl.sort.RecordBatchData;
+import org.apache.drill.exec.record.BatchSchema.SelectionVectorMode;
+import org.apache.drill.exec.vector.ValueVector;
+import org.apache.drill.exec.vector.complex.UnionVector;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Utility class for dealing with changing schemas
+ */
+public class SchemaUtil {
+
+ /**
+ * Returns the merger of schemas. The merged schema will include the
union all columns. If there is a type conflict
+ * between columns with the same schemapath but different types, the
merged schema will contain a Union type.
+ * @param schemas
+ * @return
+ */
+ public static BatchSchema mergeSchemas(BatchSchema... schemas) {
+ Map<SchemaPath,Set<MinorType>> typeSetMap = Maps.newLinkedHashMap();
+
+ for (BatchSchema s : schemas) {
+ for (MaterializedField field : s) {
+ SchemaPath path = field.getPath();
+ Set<MinorType> currentTypes = typeSetMap.get(path);
+ if (currentTypes == null) {
+ currentTypes = Sets.newHashSet();
+ typeSetMap.put(path, currentTypes);
+ }
+ MinorType newType = field.getType().getMinorType();
+ if (newType == MinorType.UNION) {
+ for (MinorType subType : field.getType().getSubTypeList()) {
+ currentTypes.add(subType);
+ }
+ } else {
+ currentTypes.add(newType);
+ }
+ }
+ }
+
+ List<MaterializedField> fields = Lists.newArrayList();
+
+ for (SchemaPath path : typeSetMap.keySet()) {
+ Set<MinorType> types = typeSetMap.get(path);
+ if (types.size() > 1) {
--- End diff --
Isn't it possible two different map types would be added above? If so, it
seems like we would produce a union when we shouldn't.
> Handle schema changes in ExternalSort
> -------------------------------------
>
> Key: DRILL-4081
> URL: https://issues.apache.org/jira/browse/DRILL-4081
> Project: Apache Drill
> Issue Type: Improvement
> Reporter: Steven Phillips
> Assignee: Steven Phillips
>
> This improvement will make use of the Union vector to handle schema changes.
> When a new schema appears, the schema will be "merged" with the previous
> schema. The result will be a new schema that uses Union type to store the
> columns where this is a type conflict. All of the batches (including the
> batches that have already arrived) will be coerced into this new schema.
> A new comparison function will be included to handle the comparison of Union
> type. Comparison of union type will work as follows:
> 1. All numeric types can be mutually compared, and will be compared using
> Drill implicit cast rules.
> 2. All other types will not be compared against other types, but only among
> values of the same type.
> 3. There will be an overall precedence of types with regards to ordering.
> This precedence is not yet defined, but will be as part of the work on this
> issue.
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