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Subject [GitHub] [flink] wuchong commented on a change in pull request #7969: [FLINK-11896] [table-planner-blink] Introduce stream physical nodes
Date Thu, 14 Mar 2019 12:16:05 GMT
wuchong commented on a change in pull request #7969: [FLINK-11896] [table-planner-blink] Introduce
stream physical nodes
URL: https://github.com/apache/flink/pull/7969#discussion_r265539811

 File path: flink-table/flink-table-planner-blink/src/main/scala/org/apache/flink/table/plan/nodes/physical/stream/StreamExecGroupAggregateBase.scala
 @@ -0,0 +1,50 @@
+ * 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
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.flink.table.plan.nodes.physical.stream
+import org.apache.calcite.plan.{RelOptCluster, RelTraitSet}
+import org.apache.calcite.rel.{RelNode, SingleRel}
+import org.apache.calcite.rel.core.Aggregate
+  * Base stream physical RelNode for unbounded group aggregate.
+  *
+  * <P>There are two differences between stream group aggregate and [[Aggregate]]:
+  * 1. stream group aggregate supports two-stage aggregation to reduce shuffle data:
+  * local-aggregation and global-aggregation.
+  * local-aggregation produces a partial result for each group before shuffle,
+  * and then global-aggregation produces final result based on shuffled partial result.
+  * Two-stage aggregation is enabled only if all aggregate functions are splittable.
+  * (e.g. SUM, AVG, MAX) see [[org.apache.calcite.sql.SqlSplittableAggFunction]] for more
+  * 2. stream group aggregate supports partial-final aggregation to resolve data-skew for
+  * distinct agg. partial-aggregation produces a partial distinct agg result for each bucket
+  * and then final-aggregation produces final result based on partial result.
+  * Both partial-aggregation and final-aggregation need to shuffle data.
+  * partial-final aggregation is enabled only if all distinct aggregate calls are mergeable.
 Review comment:
   I think the local global can be enabled when all aggregate calls are mergeable. And the
partial final can be enabled when all aggregates are splittable.

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