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Integrating with Spark extensions

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Feature available since 1.11.

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To get even better lineage coverage for Spark extensions, we recommend implementing lineage extraction directly within the extensions' code and this page contains documentation on that.

Spark ecosystem comes with a plenty of extensions that affect lineage extraction logic. spark-interfaces-scala package contains Scala traits which can be implemented on the extension's side to generate high quality metadata for OpenLineage events.

In general, a mechanism works in a following way:

  • Package spark-interfaces-scala is a simple and lightweight. Its only purpose is to contain methods to generate OpenLineage model objects (like facets, datasets) programmatically and interfaces' definitions (Scala traits) to expose lineage information from nodes of Spark logical plan.
  • Any extension that adds custom node to Spark logical plan can implement the interfaces.
  • Spark OpenLineage integration, when traversing logical plan tree, checks if its nodes implement those interfaces and uses their methods to extract lineage metadata from those nodes.

Problem definition​

OpenLineage Spark integration is based on openlineage-spark-*.jar library attached to a running Spark job. The library traverses Spark logical plan on run state updates to generate OpenLineage events. While traversing plan's tree, the library extracts input and output datasets as well as other interesting aspects of this particular job, run or datasets involved in the processing. Extraction code for each node is contained within openlineage-spark.jar.

Two main issues with this approach are:

  • Spark ecosystem comes with plenty of extensions and many of them add custom nodes into the logical plan of the query executed. These nodes need to be traversed and understood by openlineage-spark to extract lineage out of them. This brings serious complexity to the code base. Not only OpenLineage has to cover multiple Spark versions, but also each Spark version supports multiple versions of multiple extensions.

  • Spark extensions know a lot of valuable metadata that can be published within OpenLineage events. It makes sense to allow extensions publish facets on their own. This issue contains great example of useful aspects that can be retrieved from Iceberg extension.

Solution​

A remedy to the problems above is to migrate lineage extraction logic directly to Spark LogicalPlan nodes. The advantages of this approach are:

  • One-to-one version matching - there is no further need for a single integration code to support multiple versions of a Spark extension.
  • Avoid breaking changes - this approach limits amount of upgrades that break integration between openlineage-spark and other extensions, as lineage extraction code is directly put into extensions codebase which assures that changes on the Spark extension side are not breaking it.

spark-interfaces-scala package contains traits that shall be implemented as well as extra utility classes to let integrate OpenLineage within any Spark extension.

Package code should not be shipped with extension that implements traits. Dependency should be marked as compile-only. Implementation of the code calling the methods should be responsible for providing spark-interfaces-scala on the classpath.

Please note that this package as well as the traits should be considered experimental and may evolve in the future. All the current logic has been put into *.scala.v1 package. First, it is possible we develop the same interfaces in Java. Secondly, in case of non-compatible changes, we are going to release v2 interfaces. We're aiming to support different versions within spark integration.

Extracting lineage from plan nodes​

The easy way - return all the metadata about dataset​

Spark optimized logical plan is a tree created of LogicalPlan nodes. Oftentimes, it is a Spark extension internal class that implements LogicalPlan and becomes node within a tree. In this case, it is reasonable to implement lineage extraction logic directly within that class.

Two interfaces have been prepared:

  • io.openlineage.spark.builtin.scala.v1.InputLineageNode with getInputs method,
  • io.openlineage.spark.builtin.scala.v1.OutputLineageNode with getOutputs method.

They return list of InputDatasetWithFacets and OutputDatasetWithFacets respectively. Each trait has methods to expose dataset facets as well facets that relate to particular dataset only in the context of current run, like amount of bytes read from a certain dataset.

When extracting dataset name and namespace is non-trivial​

The simple approach is to let the extension provide dataset identifier containing namespace as name. However, in some cases this can be cumbersome. For example, within Spark's codebase there are several nodes whose output dataset is DatasourceV2Relation and extracting dataset's name and namespace from such nodes includes non-trivial logic. In such scenarios, it does not make sense to require an extension to re-implement the logic already present within spark-openlineage code. To solve this, the traits introduce datasets with delegates which don't contain exact dataset identifier with name and namespace. Instead, they contain pointer to other member of the plan where spark-openlineage should extract identifier from.

For this scenario, case classes InputDatasetWithDelegate and OutputDatasetWithDelegate have been created. They allow assigning facets to a dataset, while still letting other code to extract metadata for the same dataset. The classes contain node object property which defines node within logical plan to contain more metadata about the dataset. In other words, returning a delegate will make OpenLineage Spark integration extract lineage from the delegate and enrich it with facets attached to a delegate.

An example implementation for ReplaceIcebergData node:

override def getOutputs(context: OpenLineageContext): List[OutputDatasetWithFacets] = {
    if (!table.isInstanceOf[DataSourceV2Relation]) {
      List()
    } else {
      val relation = table.asInstanceOf[DataSourceV2Relation]
      val datasetFacetsBuilder: DatasetFacetsBuilder = {
        new OpenLineage.DatasetFacetsBuilder()
          .lifecycleStateChange(
          context
            .openLineage
            .newLifecycleStateChangeDatasetFacet(
              OpenLineage.LifecycleStateChangeDatasetFacet.LifecycleStateChange.OVERWRITE,
              null
            )
        )
      }
      
      // enrich dataset with additional facets like a dataset version
      DatasetVersionUtils.getVersionOf(relation) match {
        case Some(version) => datasetFacetsBuilder.version(
          context
            .openLineage
            .newDatasetVersionDatasetFacet(version)
        )
        case None =>
      }

      // return output dataset while pointing that more dataset details shall be extracted from
      // `relation` object.
      List(
        OutputDatasetWithDelegate(
          relation,
          datasetFacetsBuilder,
          new OpenLineage.OutputDatasetOutputFacetsBuilder()
        )
      )
    }
  }

When extension implements a relation within standard LogicalRelation​

In this scenario, Spark extension is using standard LogicalRelation node within the logical plan. However, the node may contain extension's specific relation property which extends org.apache.spark.sql.sources.BaseRelation. In this case, we allow BaseRelation implementation to implement io.openlineage.spark.builtin.scala.v1.LineageRelation interface.

When extension implements a provider to create relations​

An extension can contain implementation of org.apache.spark.sql.sources.RelationProvider which again does not use any custom nodes within the logical plan, but provides classes to create relations. To support this scenario, io.openlineage.spark.builtin.scala.v1.LineageDatasetProvider can be implemented.

When extension uses Spark DataSource v2 API​

Some extensions rely on Spark DataSource V2 API and implement TableProvider, Table, ScanBuilder etc. that are used within Spark to create DataSourceV2Relation instances.

A logical plan node DataSourceV2Relation contains Table field with a properties map of type Map<String, String>. openlineage-spark uses this map to extract dataset information for lineage event from DataSourceV2Relation. It is checking for the properties openlineage.dataset.name and openlineage.dataset.namespace. If they are present, it uses them to identify a dataset. Please be aware that namespace and name need to conform to naming convention.

Properties can be also used to pass any dataset facet. For example:

openlineage.dataset.facets.customFacet={"property1": "value1", "property2": "value2"}

will enrich dataset with customFacet:

"inputs": [{
"name": "...",
"namespace": "...",
"facets": {
    "customFacet": {
        "property1": "value1",
        "property2": "value2",
        "_producer": "..."
    },
    "schema": { }
}]

Column Level Lineage​

Lineage is extracted from the optimized logical plan. The plan is a tree with the root being the output dataset and leaves the input datasets. In order to collect column level lineage we need to track dependencies between input and output fields.

Each node within plan has to understand which input attributes it consumes and how they affect output attributes produced by the node. Attribute fields within plan are identified by ExprId. In order to build column level lineage, dependencies between input and output attributes for each plan's node need to be identified.

In order to emit column level lineage from a given spark node, io.openlineage.spark.builtin.scala.v1.ColumnLevelLineageNode trait has to be implemented. The trait should implement following methods

  • def columnLevelLineageInputs(context: OpenLineageContext): List[DatasetFieldLineage]
  • def columnLevelLineageOutputs(context: OpenLineageContext): List[DatasetFieldLineage]
  • columnLevelLineageDependencies(context: OpenLineageContext): List[ExpressionDependency]

First two methods are used to identify input and output fields as well as matching the fields to expressions which use the fields. Returned field lineage can contain identifier, which is mostly field name, but can also be represented by a delegate object pointing to expression where the identifier shall be extracted from.

ExpressionDependency allows matching, for each Spark plan node, input expressions onto output expressions. Having all the inputs and outputs identified, as well as intermediate dependencies between the expressions used, allow building column level lineage facet.

Code below contains an example of ColumnLevelLineageNode within Iceberg's MergeRows class that implements MERGE INTO for Spark 3.4:

case class MergeRows(
    ...,
    matchedOutputs: Seq[Seq[Seq[Expression]]],
    notMatchedOutputs: Seq[Seq[Expression]],
    output: Seq[Attribute],
    child: LogicalPlan
) extends UnaryNode with ColumnLevelLineageNode {
  
    override def columnLevelLineageDependencies(context: OpenLineageContext): List[ExpressionDependency] = {
      val deps: ListBuffer[ExpressionDependency] = ListBuffer()

      // For each matched and not-matched outputs `ExpressionDependencyWithDelegate` is created
      // This means for output expression id `attr.exprId.id`, `expr` node needs to be examined to 
      // detect input expression ids. 
      output.zipWithIndex.foreach {
        case (attr: Attribute, index: Int) =>
          notMatchedOutputs
            .toStream
            .filter(exprs => exprs.size > index)
            .map(exprs => exprs(index))
            .foreach(expr => deps += ExpressionDependencyWithDelegate(OlExprId(attr.exprId.id), expr))
          matchedOutputs
            .foreach {
              matched =>
                matched
                  .toStream
                  .filter(exprs => exprs.size > index)
                  .map(exprs => exprs(index))
                  .foreach(expr => deps += ExpressionDependencyWithDelegate(OlExprId(attr.exprId.id), expr))
            }
      }

      deps.toList
    }

    override def columnLevelLineageInputs(context: OpenLineageContext): List[DatasetFieldLineage] = {
      // Delegates input field extraction to other logical plan node
      List(InputDatasetFieldFromDelegate(child))
    }

    override def columnLevelLineageOutputs(context: OpenLineageContext): List[DatasetFieldLineage] = {
      // For each output attribute return its name and ExprId assigned to it.
      // We're aiming for lineage traits to stay Spark version agnostic and don't want to rely 
      // on Spark classes. That's why `OlExprId` is used to pass `ExprId`
      output.map(a => OutputDatasetField(a.name, OlExprId(a.exprId.id))).toList
    }
  }

Please note that ExpressionDependency can be extended in the future to contain more information on how inputs were used to produce a certain output attribute.