Github user rxin commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19269#discussion_r140379971
  
    --- Diff: 
sql/core/src/main/java/org/apache/spark/sql/sources/v2/writer/DataSourceV2Writer.java
 ---
    @@ -0,0 +1,71 @@
    +/*
    + * 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.spark.sql.sources.v2.writer;
    +
    +import org.apache.spark.annotation.InterfaceStability;
    +import org.apache.spark.sql.Row;
    +import org.apache.spark.sql.SaveMode;
    +import org.apache.spark.sql.sources.v2.DataSourceV2Options;
    +import org.apache.spark.sql.sources.v2.WriteSupport;
    +import org.apache.spark.sql.types.StructType;
    +
    +/**
    + * A data source writer that is returned by
    + * {@link WriteSupport#createWriter(StructType, SaveMode, 
DataSourceV2Options)}.
    + * It can mix in various writing optimization interfaces to speed up the 
data saving. The actual
    + * writing logic is delegated to {@link WriteTask} that is returned by 
{@link #createWriteTask()}.
    + *
    + * The writing procedure is:
    + *   1. Create a write task by {@link #createWriteTask()}, serialize and 
send it to all the
    + *      partitions of the input data(RDD).
    + *   2. For each partition, create a data writer with the write task, and 
write the data of the
    --- End diff --
    
    That doesn't really help if one of the task fails and gets relaunched.



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