[SPARK-26356][SQL] remove SaveMode from data source v2 #24233

cloud-fan · 2019-03-28T04:46:13Z

What changes were proposed in this pull request?

In data source v1, save mode specified in DataFrameWriter is passed to data source implementation directly, and each data source can define its own behavior about save mode. This is confusing and we want to get rid of save mode in data source v2.

For data source v2, we expect data source to implement the TableCatalog API, and end-users use SQL(or the new write API described in this doc) to acess data sources. The SQL API has very clear semantic and we don't need save mode at all.

However, for simple data sources that do not have table management (like a JIRA data source, a noop sink, etc.), it's not ideal to ask them to implement the TableCatalog API, and throw exception here and there.

TableProvider API is created for simple data sources. It can only get tables, without any other table management methods. This means, it can only deal with existing tables.

TableProvider fits well with DataStreamReader and DataStreamWriter, as they can only read/write existing tables. However, TableProvider doesn't fit DataFrameWriter well, as the save mode requires more than just get table. More specifically, ErrorIfExists mode needs to check if table exists, and create table. Ignore mode needs to check if table exists. When end-users specify ErrorIfExists or Ignore mode and write data to TableProvider via DataFrameWriter, Spark fails the query and asks users to use Append or Overwrite mode.

The file source is in the middle of TableProvider and TableCatalog: it's simple but it can check table(path) exists and create table(path). That said, file source supports all the save modes.

Currently file source implements TableProvider, and it's not working because TableProvider doesn't support ErrorIfExists and Ignore modes. Ideally we should create a new API for path-based data sources, but to unblock the work of file source v2 migration, this PR proposes to special-case file source v2 in DataFrameWriter, to make it work.

This PR also removes SaveMode from data source v2, as now only the internal file source v2 needs it.

How was this patch tested?

existing tests

cloud-fan · 2019-03-28T04:48:41Z

sql/core/src/test/scala/org/apache/spark/sql/sources/v2/DataSourceV2Suite.scala

          assert(!new File(sessionPath).exists)
          checkAnswer(spark.read.format(format).option("path", optionPath).load(), df)
        }
      }
    }
  }
-
-  test("SPARK-25700: do not read schema when writing in other modes except append and overwrite") {


This test is not needed anymore, as ErrorIfExists and Ignore modes are unsupported now.

cloud-fan · 2019-03-28T04:49:03Z

cc @rdblue @gengliangwang @gatorsmile

SparkQA · 2019-03-28T05:04:30Z

Test build #104036 has finished for PR 24233 at commit 2018ac2.

This patch fails to generate documentation.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2019-03-28T07:05:01Z

Test build #104037 has finished for PR 24233 at commit 3f38569.

This patch fails due to an unknown error code, -9.
This patch merges cleanly.
This patch adds no public classes.

cloud-fan · 2019-03-28T07:14:54Z

retest this please

SparkQA · 2019-03-28T10:28:47Z

Test build #104040 has finished for PR 24233 at commit 3f38569.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

gengliangwang · 2019-03-28T11:35:19Z

...e/src/main/scala/org/apache/spark/sql/execution/datasources/v2/WriteToDataSourceV2Exec.scala

 import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.catalyst.expressions.Attribute
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.execution.{SparkPlan, UnaryExecNode}
 import org.apache.spark.sql.sources.{AlwaysTrue, Filter}
 import org.apache.spark.sql.sources.v2.SupportsWrite
-import org.apache.spark.sql.sources.v2.writer.{BatchWrite, DataWriterFactory, SupportsDynamicOverwrite, SupportsOverwrite, SupportsSaveMode, SupportsTruncate, WriteBuilder, WriterCommitMessage}
+import org.apache.spark.sql.sources.v2.writer.{BatchWrite, DataWriterFactory, SupportsDynamicOverwrite, SupportsOverwrite, SupportsTruncate, WriteBuilder, WriterCommitMessage}


Nit: import org.apache.spark.sql.sources.v2.writer._

I don't agree with this.

Wildcard imports make it difficult to cherry-pick commits and increase conflicts. It is also difficult to see where symbols are coming from and pollutes the namespace with everything in a package instead of just the required names.

For example, I recently hit problems adding a logical package for expressions because of places that imported expressions._ along with plans._.

gengliangwang · 2019-03-28T17:24:58Z

+1 on the proposal.

gengliangwang · 2019-03-28T17:46:35Z

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/noop/NoopDataSource.scala

-private[noop] object NoopWriteBuilder extends WriteBuilder
-  with SupportsSaveMode with SupportsTruncate {
-  override def mode(mode: SaveMode): WriteBuilder = this
+private[noop] object NoopWriteBuilder extends WriteBuilder with SupportsTruncate {


Since now DSV2(except file sources) can only write to an existing table, here the write path of NoopDataSource will still fail (analyzer rule ResolveOutputRelation)

SparkQA · 2019-03-28T21:04:59Z

Test build #104056 has finished for PR 24233 at commit 7a7c790.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2019-03-29T01:57:08Z

Test build #104061 has finished for PR 24233 at commit 740faa1.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2019-03-29T04:46:59Z

Test build #104071 has finished for PR 24233 at commit 4bd5aad.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

gengliangwang · 2019-03-29T07:38:20Z

retest this please.

SparkQA · 2019-03-29T11:48:42Z

Test build #104083 has finished for PR 24233 at commit 4bd5aad.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

dongjoon-hyun · 2019-03-31T05:43:29Z

Retest this please.

SparkQA · 2019-03-31T07:05:02Z

Test build #104132 has finished for PR 24233 at commit 4bd5aad.

This patch fails due to an unknown error code, -9.
This patch merges cleanly.
This patch adds no public classes.

HyukjinKwon · 2019-04-01T01:15:17Z

retest this please

SparkQA · 2019-04-01T05:22:13Z

Test build #104150 has finished for PR 24233 at commit 4bd5aad.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

rdblue · 2019-04-01T19:46:36Z

...alyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala

+    table.resolved && query.resolved && {
+      // When the table schema is empty, skip the schema check.
+      // TODO: introduce a table capability to disable schema check.
+      table.schema.isEmpty || {


Why is this necessary for removing SaveMode? It seems unrelated.

I think that we should add the table capability instead of adding this check. What does this unblock?

The noop data source reports its schema as empty, but can accept input data set of any schema.

Previously, SupportsSaveMode was a special case, and we skip schema check for it. Now, only file source is a special case, and schema check is applied to noop data source as well.

It sounds like this commit depends on adding a capability to turn off schema validation. That commit should go in first to avoid adding code that we have to remember to revert later.

rdblue · 2019-04-01T19:48:55Z

sql/core/src/main/java/org/apache/spark/sql/sources/v2/TableProvider.java

@@ -24,7 +24,7 @@

 /**
 * The base interface for v2 data sources which don't have a real catalog. Implementations must
- * have a public, 0-arg constructor.
+ * have a public, 0-arg constructor, and can only deal with existing tables.


The phrase "deal with" is not very specific. I think it would be better to say what these tables can be used for: data operations like read, append, delete, and overwrite. Not operations that require metadata changes.

rdblue · 2019-04-01T19:50:02Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

+        // the save modes, which violates the semantic of `TableProvider`. Here we special-case
+        // file source and pass the save mode to file source directly. This hack can be removed
+        // after we figure out a general interface for path-based data sources.
+        case table: FileTable =>


Why is this hack necessary? Why not put off v2 support for path-based tables?

Because we want to migrate file source to v2, to validate the API of Table, ScanBuilder, WriteBuilder, etc.

This hack is just to work around the issue that we do not have a proper entry API for path-based data source, which I believe we will have later on.

I think this is not a bad idea. We can unblock the file source migration, and we can keep the DS v2 clean (FileTable is an internal class). Besides that this hack will be removed once we have path-based API in DS v2.

File sources do not use v2 by default, so this is not a necessary change for this commit. I think it should be in a separate PR. We can discuss whether it is a good idea to add this hack in the next DSv2 sync.

Please remove it from this PR.

I'm adding this to my agenda for the sync-up.

I believe that we agreed in the sync-up to remove this hack. Is there a reason why it is still included?

I explained in the comment: #24233 (comment)

Removing the hack breaks several tests and I'd like to do it in another PR. Since SupportsSaveMode is a hack, which means we already have a hack for file source v2 in DataFrameWriter.save. To keep the PR small, I think it's better to still keep the hack(it's not creating a new hack) and open a new PR to remove it and update the tests.

rdblue · 2019-04-01T19:55:23Z

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/noop/NoopSuite.scala

@@ -54,7 +56,7 @@ class NoopSuite extends SharedSQLContext {
          accum.add(1)
          x
        }
-        .write.format("noop").save()
+        .write.format("noop").mode("append").save()


Can we change the default mode for v2 to append if no mode is set? That seems more reasonable than always requiring mode("append").

Personally I support it, but I'd like to do it in another PR, as we expect to have discussions about backward compatibility for changing the default mode.

Okay, then I think this PR depends on the PR to make append the default mode for v2. Please get that in first.

Otherwise, this PR will make unnecessary changes to several places and we will have to roll those changes back to make append the default mode.

what if we end up with not changing the default mode (e.g. the community doesn't agree with it)? do you think that's a blocker to forbid ErrorIfExists and Ignore mode for TableProvider?

No, I don't think so. We would just have to make changes like this one. My motivation is to avoid making these changes because this touches several files just to set the mode to append.

We can't change the default like this. It'd be a huge nightmare for users to upgrade, because it's a subtle semantic change. If we want to piss off all Spark users that write data pipelines, changing the default from one to another here is a great way to achieve that.

We can however introduce new APIs to make it more obvious what's happening.

The proposal is only to change the default when using v2. If we don't change the default for v2, then the default is to always fail, which I think is worse.

SparkQA · 2019-04-02T07:05:01Z

Test build #104186 has finished for PR 24233 at commit 83d199d.

This patch fails due to an unknown error code, -9.
This patch merges cleanly.
This patch adds no public classes.

SparkQA · 2019-05-17T19:46:09Z

Test build #105498 has finished for PR 24233 at commit 22ba355.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

rdblue · 2019-05-17T19:58:35Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

   * </ul>
+   * <p>
+   * When writing to data source v1, the default option is `ErrorIfExist`. When writing to data
+   * source v2, the default option is `Append`.


I think @rxin objected to changing the default mode for DSv2. Has that changed?

I think that this is a good idea because the most sensible default for v2 is to append if no mode is set, instead of failing because the mode is not supported. This doesn't change v1 behavior, so I think it is okay.

I think @rxin has a concern about breaking existing ETL pipelines. Now we only change the default mode for DS v2(exclude file sources), I think there is no compatibility issue.

rdblue · 2019-05-17T20:02:53Z

sql/core/src/test/scala/org/apache/spark/sql/sources/v2/DataSourceV2Suite.scala

@@ -219,14 +219,14 @@ class DataSourceV2Suite extends QueryTest with SharedSQLContext {
        assert(spark.read.format(cls.getName).option("path", path).load().collect().isEmpty)

        spark.range(10).select('id as 'i, -'id as 'j).write.format(cls.getName)
-          .option("path", path).save()
+          .option("path", path).mode("append").save()


I don't think this change is needed because the default mode for v2 is append.

Before my PR, we write the files twice: once without the save mode, once with append mode.

Now I switch order, to make sure that the second write doesn't specify save mode, and prove the default mode is append.

cloud-fan · 2019-05-22T16:12:59Z

Note that, file source v2 is still supported in DataFrameWriter after this PR. In a previous data source v2 community sync, we agreed to not support file source v2 in DataFrameWriter, until we implement a path-based data source v2 API.

I think this is out of the scope of this PR, which aims to remove the SupportsSaveMode. We should open another PR to remove the support of file source v2 in DataFrameWriter, and update the failed tests.

rdblue · 2019-05-23T01:55:52Z

@cloud-fan, I don't recall that conclusion from a sync. Can you quote from the notes that you're talking about?

I'm fine fixing this in a follow-up, as long as there's a blocker filed so that this doesn't go into the 3.0 release.

cloud-fan · 2019-05-23T09:01:57Z

Let me quote something from your meeting notes:

PR #24233: Remove SaveMode
Ryan: This PR has a hack that passes SaveMode directly to file sources. Because the behavior of v1 is unknown, this should not be included in a release.
Wenchen: This is needed in order to use v2 file sources. Intent is migrate the file source to provide a reference implementation. Without the hack, v2 sources can’t be used (by default) because we know it [v2] is broken [i.e., can’t run CTAS].
Ryan: v2 isn’t broken. The only problem is path-based tables because we don’t know how they should behave [Gengliang is looking into this]. Catalog tables aren’t broken so we should focus on getting that support done.
Russel/Matt: is this needed for current tests to pass?
Wenchen: no, tests run using v1.
Russel: +1 for not including the hack.
Ryan: Also, tests for the new plans will require an in-memory source that will be a cleaner reference implementation.

At that time, I didn't realize that we do have test cases relying on file source v2 writing. That's why I think it's better to do it in another PR and update the tests. I've created a ticket to track it: https://issues.apache.org/jira/browse/SPARK-27815

rdblue · 2019-05-23T15:30:39Z

@cloud-fan, I don't think that issue is accurate. The problem is that there is a hack to continue passing SaveMode into some sources. That's what needs to be removed. Please update the issue to be more clear and mark it as a blocker, then I think we can move forward with this PR.

rdblue · 2019-05-23T16:09:07Z

@cloud-fan, thanks for fixing the issue. I think this is ready to go. +1 from me.

cloud-fan · 2019-05-23T16:18:47Z

Hi @dongjoon-hyun , do you have time to take a look at this please? thanks!

dongjoon-hyun · 2019-05-24T03:13:01Z

Retest this please.

dongjoon-hyun · 2019-05-24T03:20:43Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

@@ -268,9 +269,26 @@ final class DataFrameWriter[T] private[sql](ds: Dataset[T]) {

      import org.apache.spark.sql.execution.datasources.v2.DataSourceV2Implicits._
      provider.getTable(dsOptions) match {
+        // TODO: for backward compatibility reasons, the builtin file source needs to support all


Can we have an IDed TODO? TODO: -> TODO(SPARK-XXX):?

dongjoon-hyun · 2019-05-24T03:21:34Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

@@ -268,9 +269,26 @@ final class DataFrameWriter[T] private[sql](ds: Dataset[T]) {

      import org.apache.spark.sql.execution.datasources.v2.DataSourceV2Implicits._
      provider.getTable(dsOptions) match {
+        // TODO: for backward compatibility reasons, the builtin file source needs to support all
+        // the save modes, which violates the semantic of `TableProvider`. Here we special-case


nit. Here we special-case?

dongjoon-hyun · 2019-05-24T03:39:31Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

   * </ul>
+   * <p>
+   * When writing to data source v1, the default option is `ErrorIfExist`. When writing to data


nit ErrorIfExist -> ErrorIfExists

dongjoon-hyun · 2019-05-24T03:42:54Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

@@ -78,15 +80,14 @@ final class DataFrameWriter[T] private[sql](ds: Dataset[T]) {
   * @since 1.4.0
   */
  def mode(saveMode: String): DataFrameWriter[T] = {
-    this.mode = saveMode.toLowerCase(Locale.ROOT) match {
+    mode(saveMode.toLowerCase(Locale.ROOT) match {
      case "overwrite" => SaveMode.Overwrite
      case "append" => SaveMode.Append
      case "ignore" => SaveMode.Ignore
      case "error" | "errorifexists" | "default" => SaveMode.ErrorIfExists


This should be changed because "default" is not ErrorIfExists for DSv2.

Could you add a test coverage for this? It seems that we don't have yet.

dongjoon-hyun · 2019-05-24T04:26:22Z

Thank you for pinging me, @cloud-fan . Mostly, it looks good to me. I have only one concern about .mode("default") behavior, #24233 (comment) and the other comments are minor.

SparkQA · 2019-05-24T06:11:57Z

Test build #105749 has finished for PR 24233 at commit 22ba355.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

gatorsmile · 2019-05-24T06:12:40Z

sql/core/src/main/java/org/apache/spark/sql/sources/v2/TableProvider.java

@@ -26,6 +26,9 @@
 * The base interface for v2 data sources which don't have a real catalog. Implementations must
 * have a public, 0-arg constructor.
 * <p>
+ * Note that, TableProvider can only apply data operations to existing tables, like read, append,
+ * delete, and overwrite. Not operations that require metadata changes, like create/drop tables.


Not operations -> It does not support the operations

gatorsmile

LGTM

cloud-fan · 2019-05-24T12:41:18Z

@dongjoon-hyun good catch about .mode("default")! I've fixed it and added tests.

SparkQA · 2019-05-24T15:41:44Z

Test build #105761 has finished for PR 24233 at commit 15d2071.

This patch passes all tests.
This patch merges cleanly.
This patch adds no public classes.

dongjoon-hyun · 2019-05-24T17:42:06Z

sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala

+      case "append" => mode(SaveMode.Append)
+      case "ignore" => mode(SaveMode.Ignore)
+      case "error" | "errorifexists" => mode(SaveMode.ErrorIfExists)
+      case "default" => this


gatorsmile · 2019-05-24T17:44:55Z

Thanks! Merged to master.

dongjoon-hyun · 2019-05-24T17:44:59Z

sql/core/src/test/scala/org/apache/spark/sql/test/DataFrameReaderWriterSuite.scala

+      .format("org.apache.spark.sql.test")
+      .mode("default")
+      .save()
+    assert(LastOptions.saveMode === SaveMode.ErrorIfExists)


dongjoon-hyun

+1, LGTM, too.

In data source v1, save mode specified in `DataFrameWriter` is passed to data source implementation directly, and each data source can define its own behavior about save mode. This is confusing and we want to get rid of save mode in data source v2. For data source v2, we expect data source to implement the `TableCatalog` API, and end-users use SQL(or the new write API described in [this doc](https://docs.google.com/document/d/1gYm5Ji2Mge3QBdOliFV5gSPTKlX4q1DCBXIkiyMv62A/edit?ts=5ace0718#heading=h.e9v1af12g5zo)) to acess data sources. The SQL API has very clear semantic and we don't need save mode at all. However, for simple data sources that do not have table management (like a JIRA data source, a noop sink, etc.), it's not ideal to ask them to implement the `TableCatalog` API, and throw exception here and there. `TableProvider` API is created for simple data sources. It can only get tables, without any other table management methods. This means, it can only deal with existing tables. `TableProvider` fits well with `DataStreamReader` and `DataStreamWriter`, as they can only read/write existing tables. However, `TableProvider` doesn't fit `DataFrameWriter` well, as the save mode requires more than just get table. More specifically, `ErrorIfExists` mode needs to check if table exists, and create table. `Ignore` mode needs to check if table exists. When end-users specify `ErrorIfExists` or `Ignore` mode and write data to `TableProvider` via `DataFrameWriter`, Spark fails the query and asks users to use `Append` or `Overwrite` mode. The file source is in the middle of `TableProvider` and `TableCatalog`: it's simple but it can check table(path) exists and create table(path). That said, file source supports all the save modes. Currently file source implements `TableProvider`, and it's not working because `TableProvider` doesn't support `ErrorIfExists` and `Ignore` modes. Ideally we should create a new API for path-based data sources, but to unblock the work of file source v2 migration, this PR proposes to special-case file source v2 in `DataFrameWriter`, to make it work. This PR also removes `SaveMode` from data source v2, as now only the internal file source v2 needs it. existing tests Closes apache#24233 from cloud-fan/file. Authored-by: Wenchen Fan <wenchen@databricks.com> Signed-off-by: gatorsmile <gatorsmile@gmail.com>

cloud-fan commented Mar 28, 2019

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remove SaveMode from data source v2

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cloud-fan force-pushed the file branch from 2018ac2 to 3f38569 Compare March 28, 2019 05:12

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cloud-fan force-pushed the file branch from 7a7c790 to 740faa1 Compare March 28, 2019 22:35

address comment

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gengliangwang mentioned this pull request Mar 29, 2019

[SPARK-26915][SQL] DataFrameWriter.save() should write without schema validation #23836

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dongjoon-hyun approved these changes May 24, 2019

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gatorsmile closed this in 7d318bf May 24, 2019

dongjoon-hyun mentioned this pull request Oct 14, 2019

[SPARK-29442][SQL] Set default mode should override the existing mode #26094

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[SPARK-26356][SQL] remove SaveMode from data source v2 #24233

[SPARK-26356][SQL] remove SaveMode from data source v2 #24233

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cloud-fan commented Mar 28, 2019 •

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