This article introduces the new interface and the new code structure on account of the newly designed API for Connectors in Apache SeaTunnel. This helps developers quickly understand API and transformation layer improvements. On the other hand, it can guide contributors how to use the new API to develop new connectors.See this issue for details.
In order to separate from the old code, we have defined new modules for execution flow. This facilitates parallel development at the current stage, and reduces the difficulty of merging.
seatunnel-connectors-v2 connector-v2 code implementationseatunnel-translation translation layer for the connector-v2seatunnel-transform-v2 transform v2 connector implementationseatunnel-connector-v2-e2e connector v2 e2e codeseatunnel-engine-examples seatunnel connector-v2 example use Zeta local running instanceseatunnel-flink-connector-v2-example seatunnel connector-v2 example use Flink local running instanceseatunnel-spark-connector-v2-example seatunnel connector-v2 example use Spark local running instanceWe have prepared three locally executable example programs in seatunnel-examples:
seatunnel-examples/seatunnel-engine-examples/src/main/java/org/apache/seatunnel/example/engine/SeaTunnelEngineLocalExample.java, which runs on the Zeta engineseatunnel-examples/seatunnel-flink-connector-v2-example/src/main/java/org/apache/seatunnel/example/flink/v2/SeaTunnelApiExample.java, which runs on the Flink engineseatunnel-examples/seatunnel-spark-connector-v2-example/src/main/java/org/apache/seatunnel/example/spark/v2/SeaTunnelApiExample.java, which runs on the Spark engineYou can debug these examples to help you better understand the running logic of the program. The configuration files used are saved in the resources/examples folder. If you want to add your own connectors, you need to follow the steps below.
To add a new connector to the example using the Zeta engine, follow these steps:
groupId, artifactId, and version to seatunnel-examples/seatunnel-engine-examples/pom.xml (or to seatunnel-examples/seatunnel-flink-connector-v2-example/pom.xml or seatunnel-examples/seatunnel-spark-connector-v2-example/pom.xml if you want to run it on the Flink or Spark engine, respectively).scope set to test or provided, add these dependencies to seatunnel-examples/seatunnel-engine-examples/pom.xml and change the scope to compile.resources/examples.SeaTunnelEngineLocalExample.java main method.Create a new module under the seatunnel-connectors-v2 directory and name it connector-{ConnectorName}.
The pom.xml file can refer to the pom.xml file of the existing connector, and add the current sub-module to seatunnel-connectors-v2/pom.xml.
Create two packages corresponding to source and sink
package org.apache.seatunnel.connectors.seatunnel.{ConnectorName}}.source package org.apache.seatunnel.connectors.seatunnel.{ConnectorName}}.sink
add connector info to plugin-mapping.properties file in seatunnel root path.
add connector dependency to seatunnel-dist/pom.xml, so the connector jar can be find in binary package.
There are several classes that must be implemented on the source side, namely {ConnectorName}Source, {ConnectorName}SourceFactory, {ConnectorName}SourceReader; There are several classes that must be implemented on the sink side, namely {ConnectorName}Sink, {ConnectorName}SinkFactory, {ConnectorName}SinkWriter Please refer to other connectors for details
{ConnectorName}SourceFactory and {ConnectorName}SinkFactory needs to be annotated with the @AutoService (Factory.class) annotation on the class name, and in addition to the required methods, source side an additional creatSource method needs to be rewritten and sink side an additional creatSink method needs to be rewritten
{ConnectorName}Source needs to override the getProducedCatalogTables method; {ConnectorName}Sink needs to override the getWriteCatalogTable method
We have created three starter projects: seatunnel-core/seatunnel-starter, seatunnel-core/seatunnel-flink-starter, and seatunnel-core/seatunnel-spark-starter. Here you can find how to parse configuration files into executable Zeta/Flink/Spark processes.
The seatunnel-api module is used to store the new interfaces defined by the SeaTunnel API. By implementing these interfaces, developers can create SeaTunnel Connectors that support multiple engines.
We realize the conversion between SeaTunnel API and Engine API by adapting the interfaces of different engines, so as to achieve the effect of translation, and let our SeaTunnel Connector support the operation of multiple different engines. The corresponding code address, seatunnel-translation, this module has the corresponding translation layer implementation. If you are interested, you can view the code and help us improve the current code.
The API design of the current version of SeaTunnel draws on the design concept of Flink.
createSource method.factoryIdentifier is used to identify the name of the current Factory, which is also configured in the configuration file to distinguish different connectors.optionRule is used to define the parameters supported by the current connector. This method can be used to define the logic of the parameters, such as which parameters are required, which are optional, which are mutually exclusive, etc. SeaTunnel will use OptionRule to verify the validity of the user's configuration. Please refer to the Option below.@AutoService(Factory.class) annotation to TableSourceFactory.getBoundedness which determines whether the current Source is a stream Source or a batch Source, so you can specify a Source by dynamic configuration (refer to the default method), which can be either a stream or a batch.getProducedCatalogTables is used to get the schema of the data. The connector can choose to hard-code to implement a fixed schema or implement a custom schema through user-defined configuration. The latter is recommended.Use this enumerator to get the data read shard (SourceSplit) situation, different shards may be assigned to different SourceReaders to read data. Contains several key methods:
open method is used to initialize the SourceSplitEnumerator. In this method, you can initialize resources such as database connections or states.run: Used to perform a spawn SourceSplit and call SourceSplitEnumerator.Context.assignSplit: to distribute the shards to the SourceReader.addSplitsBackSourceSplitEnumerator: is required to redistribute these Splits when SourceSplit cannot be processed normally or restarted due to the exception of SourceReader.registerReaderProcess: some SourceReaders that are registered after the run is run. If there is no SourceSplit distributed at this time, it can be distributed to these new readers (yes, you need to maintain your SourceSplit distribution in SourceSplitEnumerator most of the time).handleSplitRequest: If some Readers actively request SourceSplit from SourceSplitEnumerator, this method can be called SourceSplitEnumerator.Context.assignSplit to sends shards to the corresponding Reader.snapshotState: It is used for stream processing to periodically return the current state that needs to be saved. If there is a state restoration, it will be called SeaTunnelSource.restoreEnumerator to constructs a SourceSplitEnumerator and restore the saved state to the SourceSplitEnumerator.notifyCheckpointComplete: It is used for subsequent processing after the state is successfully saved, and can be used to store the state or mark in third-party storage.handleSourceEvent is used to handle events from the SourceReader. You can customize events, such as changes in the state of the SourceReader.close is used to close the SourceSplitEnumerator and release resources.The SourceSplitEnumerator.Context is the context for the SourceSplitEnumerator, which interacts with SeaTunnel. It includes several key methods:
currentParallelism: Used to get the current task's parallelism.registeredReaders: Used to get the list of currently registered SourceReader.assignSplit: Used to assign splits to SourceReader.signalNoMoreSplits: Used to notify a SourceReader that there are no more splits.sendEventToSourceReader: Used to send events to SourceReader.getMetricsContext: Used to get the current task's MetricsContext for recording metrics.getEventListener: Used to get the current task's EventListener for sending events to SeaTunnel.The interface used to save shards. Different shards need to define different splitIds. You can implement this interface to save the data that shards need to save, such as kafka‘s partition and topic, hbase’s columnfamily and other information, which are used by SourceReader to determine Which part of the total data should be read.
The interface that directly interacts with the data source, and the action of reading data from the data source is completed by implementing this interface.
pollNext: It is the core of Reader. Through this interface, the process of reading the data of the data source and returning it to SeaTunnel is realized. Whenever you are ready to pass data to SeaTunnel, you can call the Collector.collect method in the parameter, which can be called an infinite number of times to complete a large amount of data reading. But the data format supported at this stage can only be SeaTunnelRow. Because our Source is a stream-batch integration, the Connector has to decide when to end data reading in batch mode. For example, a batch reads 100 pieces of data at a time. After the reading is completed, it needs pollNext to call in to SourceReader.Context.signalNoMoreElementnotify SeaTunnel that there is no data to read . , then you can use these 100 pieces of data for batch processing. Stream processing does not have this requirement, so most SourceReaders with integrated stream batches will have the following code:java if(Boundedness.BOUNDED.equals(context.getBoundedness())){ // signal to the source that we have reached the end of the data. context.signalNoMoreElement(); break; }
It means that SeaTunnel will be notified only in batch mode.
addSplits: Used by the framework to assign SourceSplit to different SourceReaders, SourceReader should save the obtained shards, and then pollNextread the corresponding shard data in it, but there may be times when the Reader does not read shards (maybe SourceSplit has not been generated or The current Reader is indeed not allocated), at this time, pollNextcorresponding processing should be made, such as continuing to wait.handleNoMoreSplits: When triggered, it indicates that there are no more shards, and the Connector Source is required to optionally make corresponding feedbacksnapshotStateIt: is used for stream processing to periodically return the current state that needs to be saved, that is, the fragmentation information (SeaTunnel saves the fragmentation information and state together to achieve dynamic allocation).notifyCheckpointComplete: Like notifyCheckpointAborted the name, it is a callback for different states of checkpoint.The SourceReader.Context is the context for the SourceReader, which interacts with SeaTunnel. It includes several key methods:
getIndexOfSubtask: Used to get the current Reader's subTask index.getBoundedness: Used to get the current Reader's Boundedness, whether it is stream or batch.signalNoMoreElement: Used to notify SeaTunnel that there are no more elements to read.sendSplitRequest: Used to request splits from the SourceSplitEnumerator when the Reader has no splits.sendSourceEventToEnumerator: Used to send events to the SourceSplitEnumerator.getMetricsContext: Used to get the current task's MetricsContext for recording metrics.getEventListener: Used to get the current task's EventListener for sending events to SeaTunnel.createSink method.factoryIdentifier is used to identify the name of the current Factory, which is also configured in the configuration file to distinguish different connectors.optionRule is used to define the parameters supported by the current connector. You can use this method to define the logic of the parameters, such as which parameters are required, which parameters are optional, which parameters are mutually exclusive, etc. SeaTunnel will use OptionRule to verify the validity of the user's configuration. Please refer to the Option below.@AutoService(Factory.class) annotation to the TableSinkFactory class.It is used to define the way to write data to the destination, and obtain instances such as SinkWriter and SinkCommitter through this interface. An important feature of the sink side is the processing of distributed transactions. SeaTunnel defines two different Committers: SinkCommitter used to process transactions for different subTasks SinkAggregatedCommitter. Process transaction results for all nodes. Different Connector Sinks can be selected according to component properties, whether to implement only SinkCommitter or SinkAggregatedCommitter, or both.
createWriter is used to create a SinkWriter instance. The SinkWriter is an interface that interacts with the data source, allowing data to be written to the data source through this interface.restoreWriter is used to restore the SinkWriter to its previous state during state recovery. This method is called when the task is restored.getWriteCatalogTable is used to get the SeaTunnel CatalogTable corresponding to the table written by the Sink. SeaTunnel will handle metrics-related logic based on this CatalogTable.It is used to directly interact with the output source, and provide the data obtained by SeaTunnel through the data source to the Writer for data writing.
write: Responsible for transferring data to SinkWriter, you can choose to write it directly, or write it after buffering a certain amount of data. Currently, only the data type is supported SeaTunnelRow.prepareCommit: Executed before commit, you can write data directly here, or you can implement phase one in 2pc, and then implement phase two in SinkCommitter or SinkAggregatedCommitter. What this method returns is the commit information, which will be provided SinkCommitter and SinkAggregatedCommitter used for the next stage of transaction processing.snapshotState is used to periodically return the current state to be saved during stream processing. If there is a state recovery, SeaTunnelSink.restoreWriter will be called to construct the SinkWriter and restore the saved state to the SinkWriter.abortPrepare is executed when prepareCommit fails, used to roll back the operations of prepareCommit.close is used to close the SinkWriter and release resources.The Context is the context for the SinkWriter, which interacts with SeaTunnel. It includes several key methods:
getIndexOfSubtask: Used to get the current Writer's subTask index.getNumberOfParallelSubtasks: Used to get the current task's parallelism.getMetricsContext: Used to get the current task's MetricsContext for recording metrics.getEventListener: Used to get the current task's EventListener for sending events to SeaTunnel.Used to process the data information returned by SinkWriter.prepareCommit, including the transaction information that needs to be submitted. Unlike SinkAggregatedCommitter, SinkCommitter is executed on each node. We recommend using SinkAggregatedCommitter.
commit: Used to submit the transaction information returned by SinkWriter.prepareCommit. If it fails, idempotency must be implemented to ensure that the engine retry can work normally.abort: Used to roll back the operations of SinkWriter.prepareCommit. If it fails, idempotency must be implemented to ensure that the engine retry can work normally.Used to process the data information returned by SinkWriter.prepareCommit, including the transaction information that needs to be submitted. However, it will be processed together on a single node, which can avoid the problem of inconsistency caused by the failure of the second part of the stage.
init: Used to initialize the SinkAggregatedCommitter. You can initialize some resources for the connector here, such as connecting to a database or initializing some states.restoreCommit: Used to restore the SinkAggregatedCommitter to its previous state during state recovery. This method is called when the task is restored, and we should retry committing the unfinished transactions in this method.commit: Used to submit the transaction information returned by SinkWriter.prepareCommit. If it fails, idempotency must be implemented to ensure that the engine retry can work normally.combine: Used to aggregate the transaction information returned by SinkWriter.prepareCommit and then generate aggregated transaction information.abort: Used to roll back the operations of SinkWriter.prepareCommit. If it fails, idempotency must be implemented to ensure that the engine retry can work normally.close: Used to close the SinkAggregatedCommitter and release resources.In the current version, it is recommended to implement SinkAggregatedCommitter as the first choice, which can provide strong consistency guarantee in Flink/Spark. At the same time, commit should be idempotent, and save engine retry can work normally.
When we implement TableSourceFactory and TableSinkFactory, the corresponding Option will be created. Each Option corresponds to a configuration, but different configurations will have different types. Common types can be created by directly calling the corresponding method. But if our parameter type is an object, we can use POJO to represent parameters of object type, and need to use org.apache.seatunnel.api.configuration.util.OptionMark on each parameter to indicate that this is A child Option. OptionMark has two parameters, name is used to declare the parameter name corresponding to the field. If it is empty, we will convert the small camel case corresponding to java to underscore by default, such as: myUserPassword -> my_user_password . In most cases, the default is empty. description is used to indicate the description of the current parameter. This parameter is optional. It is recommended to be consistent with the documentation. For specific examples, please refer to org.apache.seatunnel.connectors.seatunnel.assertion.sink.AssertSinkFactory.
In TableSourceFactory and TableSinkFactory, the optionRule method returns the parameter logic, which defines which parameters are supported by our connector, which parameters are required, which parameters are optional, which parameters are mutually exclusive, and which parameters are bundled required. This method will be used when we visually create the connector logic, and it will also be used to generate a complete parameter object based on the user's configured parameters, so that connector developers do not need to check each parameter in the config individually and can use it directly. You can refer to existing implementations, such as org.apache.seatunnel.connectors.seatunnel.elasticsearch.source.ElasticsearchSourceFactory. For many sources that support schema configuration, a common option is used, and if a schema is needed, you can refer to org.apache.seatunnel.api.table.catalog.CatalogTableUtil.SCHEMA.
All Connector implementations should be under the seatunnel-connectors-v2, and the examples that can be referred to at this stage are under this module.