Github user rdblue commented on a diff in the pull request:
https://github.com/apache/spark/pull/19269#discussion_r140371372
--- 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 --
Maybe Spark should be able to disable speculative tasks at runtime instead
of requiring data sources to rollback. I'd prefer that, but I don't think it is
something that needs to change now. We can always add an interface if/when it
is supported that allows data sources to communicate a lack of support for
speculation.
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