Elaborate usage of PlatformTransactionManager

[quaff]

There are many places to configure transactionManager, it's unclear whether it's mandatory or not, from my understanding, it's should be optional since dataSource is mandatory, Spring Batch could create DataSourceTransactionManager() as default, correct me if I'm wrong.

And it's unclear whether it's used for batch metadata operations or JDBC reader/writer of step, if Spring Boot's @BatchDataSource and @BatchTransactionManager are used for separated DataSource, which transactionManager should be used for StepBuilder::chunk?

spring-batch/spring-batch-core/src/main/java/org/springframework/batch/core/step/builder/StepBuilder.java

Line 118 in e1b0f15

public <I, O> SimpleStepBuilder<I, O> chunk(int chunkSize, PlatformTransactionManager transactionManager) {

[fmbenhassine]

Spring Batch could create DataSourceTransactionManager() as default, correct me if I'm wrong.

Spring Batch used to do that, but it was causing issues like #816.

it's unclear whether it's used for batch metadata operations or JDBC reader/writer of step

Those can be different: one can use a ResourcelessTransactionManager for meta-data and a JdbcTransactionManager for business data.

I will plan to clarify the docs with a note about this.