Spring-batch partitioned step duplicated processing

Question

I have thousands of records to process using spring-batch and it takes too much time for our business requirement. The logic is simply to read a CSV file record by record and do the processing.

I want to parallelise the step execution to speed up batch processing. I think the best choice would be to partition the step and execute let's say 1-100 records in one thread, 101-200 in another and so on. But instead, every thread processes all of the records.

The same happens in this very simple example:

1. 10 rows in CSV file
2. 5 threads
3. Each should process 2 records
4. Instead each processes 10 records

@Configuration
@RequiredArgsConstructor
public class JobConfig {
    private final JobBuilderFactory jobBuilderFactory;
    private final StepBuilderFactory stepBuilderFactory;

    @Value("classpath:employees.csv")
    private Resource resourceFile;

    @Bean("MyJob1")
    public Job createJob() {
        return jobBuilderFactory.get("my job 1")
            .incrementer(new RunIdIncrementer())
            .start(step())
            .build();
    }

    @Bean("MyStep1")
    public Step step() {
        return stepBuilderFactory.get("my step 1")
            .partitioner("my step 1", new SimplePartitioner())
            .partitionHandler(partitionHandler())
            .build();
    }

    @Bean("slaveStep")
    public Step slaveStep() {
        return stepBuilderFactory.get("read csv stream")
            .<Employee, Employee>chunk(1)
            .reader(flatFileItemReader())
            .processor((ItemProcessor<Employee, Employee>) employee -> {
                System.out.printf("Processed item %s%n", employee.getId());
                return employee;
            })
            .writer(list -> {
                for (Employee item : list) {
                    System.out.println(item);
                }
            })
            .build();
    }

    @StepScope
    @Bean
    public FlatFileItemReader<Employee> flatFileItemReader() {
        FlatFileItemReader<Employee> reader = new FlatFileItemReader<>();
        reader.setResource(resourceFile);

        DefaultLineMapper<Employee> lineMapper = new DefaultLineMapper<>();
        lineMapper.setFieldSetMapper(fieldSet -> {
            String[] values = fieldSet.getValues();
            return Employee.builder()
                .id(Integer.parseInt(values[0]))
                .firstName(values[1])
                .build();
        });

        lineMapper.setLineTokenizer(new DelimitedLineTokenizer(";"));
        reader.setLineMapper(lineMapper);

        return reader;
    }

    @Bean
    public PartitionHandler partitionHandler() {
        TaskExecutorPartitionHandler taskExecutorPartitionHandler = new TaskExecutorPartitionHandler();

        taskExecutorPartitionHandler.setTaskExecutor(taskExecutor());
        taskExecutorPartitionHandler.setStep(slaveStep());
        taskExecutorPartitionHandler.setGridSize(5);

        return taskExecutorPartitionHandler;
    }

    @Bean
    public TaskExecutor taskExecutor() {
        ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
        taskExecutor.setMaxPoolSize(5);
        taskExecutor.setCorePoolSize(5);
        taskExecutor.setQueueCapacity(5);
        taskExecutor.afterPropertiesSet();
        return taskExecutor;
    }
}

@SpringBootApplication
@EnableBatchProcessing
public class SpringBatchTestsApplication implements CommandLineRunner {
    private final JobLauncher jobLauncher;
    private final Job job;

    public SpringBatchTestsApplication(JobLauncher jobLauncher,
                                       @Qualifier("MyJob1") Job job) {
        this.jobLauncher = jobLauncher;
        this.job = job;
    }

    public static void main(String[] args) {
        SpringApplication.run(SpringBatchTestsApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        jobLauncher.run(job, new JobParameters());
    }
}

@Value
@Builder
public class Employee {
    private final int id;
    private final String firstName;
}

employees.csv:

1;Jakub
2;Mike
3;Pawel
4;Joana
5;Michal
6;Joe
7;Bailey
8;Bailhache
9;John
10;Eva

Example (example because the order is not important) expected output for 5 threads (gridSize):

Processed item 1
Employee(id=1, firstName=Jakub)
Processed item 2
Employee(id=2, firstName=Mike)
Processed item 3
Employee(id=3, firstName=Pawel)
Processed item 4
Employee(id=4, firstName=Joana)
Processed item 5
Employee(id=5, firstName=Michal)
Processed item 6
Employee(id=6, firstName=Joe)
Processed item 7
Employee(id=7, firstName=Bailey)
Processed item 8
Employee(id=8, firstName=Bailhache)
Processed item 9
Employee(id=9, firstName=John)
Processed item 10
Employee(id=10, firstName=Eva)

The actual output is that the above occurs 5 times.

Answer 1

This should be the solution look at the partitioner he will take care of counting the lines of the file and divde them for the reader and the usage of @Value("#{stepExecutionContext['fromLine']}") to inject in the reader the correct lines to read.

An please use injection instead of calling the methods.

@Configuration
@RequiredArgsConstructor
public class JobConfig {

    private static final Logger log = LoggerFactory.getLogger(JobConfig.class);

    private final JobBuilderFactory jobBuilderFactory;
    private final StepBuilderFactory stepBuilderFactory;

    @Value(value = "classpath:employees.csv")
    private Resource resource;

    @Bean("MyJob1")
    public Job createJob(@Qualifier("MyStep1") Step stepMaster) {
        return jobBuilderFactory.get("MyJob1")
            .incrementer(new RunIdIncrementer())
            .start(stepMaster)
            .build();
    }

    @Bean("MyStep1")
    public Step step(PartitionHandler partitionHandler, Partitioner partitioner) {
        return stepBuilderFactory.get("MyStep1")
            .partitioner("slaveStep", partitioner)
            .partitionHandler(partitionHandler)
            .build();
    }

    @Bean("slaveStep")
    public Step slaveStep(FlatFileItemReader<Employee> reader) {
        return stepBuilderFactory.get("slaveStep")
            .<Employee, Employee>chunk(1)
            .reader(reader)
            .processor((ItemProcessor<Employee, Employee>) employee -> {
                System.out.printf("Processed item %s%n", employee.getId());
                return employee;
            })
            .writer(list -> {
                for (Employee item : list) {
                    System.out.println(item);
                }
            })
            .build();
    }
    
    @Bean
    public Partitioner partitioner() {
        return gridSize -> {
            Map<String, ExecutionContext> result = new HashMap<>();
            int lines = 0;
            try(BufferedReader reader = new BufferedReader(new InputStreamReader(resource.getInputStream()))) {
                while (reader.readLine() != null) lines++;
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            int range = lines / gridSize;
            int remains = lines % gridSize;
            int fromLine = 0;
            int toLine = range;
            for (int i = 1; i <= gridSize; i++) {
                if(i == gridSize) {
                    toLine += remains;
                }
                ExecutionContext value = new ExecutionContext();
                value.putInt("fromLine", fromLine);
                value.putInt("toLine", toLine);
                fromLine = toLine;
                toLine += range;
                result.put("partition" + i, value);
            }
            return result;
        };
    }
        

    @StepScope
    @Bean
    public FlatFileItemReader<Employee> flatFileItemReader(@Value("#{stepExecutionContext['fromLine']}") int startLine, @Value("#{stepExecutionContext['toLine']}") int lastLine) {
        FlatFileItemReader<Employee> reader = new FlatFileItemReader<>();
        reader.setResource(resource);

        DefaultLineMapper<Employee> lineMapper = new DefaultLineMapper<>();
        lineMapper.setFieldSetMapper(fieldSet -> {
            String[] values = fieldSet.getValues();
            return Employee.builder()
                    .id(Integer.parseInt(values[0]))
                    .firstName(values[1])
                    .build();
        });

        lineMapper.setLineTokenizer(new DelimitedLineTokenizer(";"));
        reader.setLineMapper(lineMapper);
        reader.setCurrentItemCount(startLine);
        reader.setMaxItemCount(lastLine);

        return reader;
    }

    @Bean
    public PartitionHandler partitionHandler(@Qualifier("slaveStep") Step step, TaskExecutor taskExecutor) {
        TaskExecutorPartitionHandler taskExecutorPartitionHandler = new TaskExecutorPartitionHandler();

        taskExecutorPartitionHandler.setTaskExecutor(taskExecutor);
        taskExecutorPartitionHandler.setStep(step);
        taskExecutorPartitionHandler.setGridSize(5);

        return taskExecutorPartitionHandler;
    }

    @Bean
    public TaskExecutor taskExecutor() {
        ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
        taskExecutor.setMaxPoolSize(5);
        taskExecutor.setCorePoolSize(5);
        taskExecutor.setQueueCapacity(5);
        taskExecutor.afterPropertiesSet();
        return taskExecutor;
    }
    
}

Answer 2

I don't know whether my solution is the best but it is worked.

I added two parameters as global in JobConfig class:

private int startLine = -1;
private int lastLine = 1;

Then I set these parameters to reader in flatFileItemReader method:

reader.setCurrentItemCount(startLine);
reader.setMaxItemCount(lastLine);
startLine+=2;
lastLine+=2;

All code:

@Configuration
@RequiredArgsConstructor
public class JobConfig {
    private final JobBuilderFactory jobBuilderFactory;
    private final StepBuilderFactory stepBuilderFactory;

    private int startLine = -1;
    private int lastLine = 1;

    @Value("classpath:employees.csv")
    private Resource resourceFile;

    @Bean("MyJob1")
    public Job createJob() {
        return jobBuilderFactory.get("my job 1")
                .incrementer(new RunIdIncrementer())
                .start(step())
                .build();
    }

    @Bean("MyStep1")
    public Step step() {
        return stepBuilderFactory.get("my step 1")
                .partitioner("my step 1", new SimplePartitioner())
                .partitionHandler(partitionHandler())
                .build();
    }

    @Bean("slaveStep")
    public Step slaveStep() {
        return stepBuilderFactory.get("read csv stream")
                .<Employee, Employee>chunk(1)
                .reader(flatFileItemReader())
                .processor((ItemProcessor<Employee, Employee>) employee -> {
                    System.out.printf("Processed item %s%n", employee.getId());
                    return employee;
                })
                .writer(list -> {
                    for (Employee item : list) {
                        //System.out.println(item);
                    }
                })
                .build();
    }

    @StepScope
    @Bean
    public FlatFileItemReader<Employee> flatFileItemReader() {
        FlatFileItemReader<Employee> reader = new FlatFileItemReader<>();
        reader.setResource(resourceFile);

        DefaultLineMapper<Employee> lineMapper = new DefaultLineMapper<>();
        lineMapper.setFieldSetMapper(fieldSet -> {
            String[] values = fieldSet.getValues();
            return Employee.builder()
                    .id(Integer.parseInt(values[0]))
                    .firstName(values[1])
                    .build();
        });

        lineMapper.setLineTokenizer(new DelimitedLineTokenizer(";"));
        reader.setLineMapper(lineMapper);
        reader.setCurrentItemCount(startLine);
        reader.setMaxItemCount(lastLine);
        startLine+=2;
        lastLine+=2;
        return reader;
    }

    @Bean
    public PartitionHandler partitionHandler() {
        TaskExecutorPartitionHandler taskExecutorPartitionHandler = new TaskExecutorPartitionHandler();

        taskExecutorPartitionHandler.setTaskExecutor(taskExecutor());
        taskExecutorPartitionHandler.setStep(slaveStep());
        taskExecutorPartitionHandler.setGridSize(5);

        return taskExecutorPartitionHandler;
    }

    @Bean
    public TaskExecutor taskExecutor() {
        ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
        taskExecutor.setMaxPoolSize(5);
        taskExecutor.setCorePoolSize(5);
        taskExecutor.setQueueCapacity(5);
        taskExecutor.afterPropertiesSet();
        return taskExecutor;
    }
}

Answer 3

I think in principle my initial idea to partition reading from the CSV file is wrong. Partitioning is effective when it is easy to partition the resource from which the reading will be performed.

1. For example database table. Every thread would read the separate range of the records.
2. Several files. Every thread would read the separate file.

However, partitioning the file where one thread would read a specific range of the records will not necessarily mean any performance gain: Split one large file into multiple InputStream(s) to be processed in multithreading in Java

One-line improvement to employ several threads into batch processing would be to add SimpleAsyncTaskExecutor . Each chunk of items then is read, processed and written in a separate thread:

@Bean("MyStep1")
public Step step() {
    return stepBuilderFactory.get("my step 1")
        .<Employee, Employee>chunk(1)
        .reader(flatFileItemReader())
        .processor((ItemProcessor<Employee, Employee>) employee -> {
            System.out.printf("Processed item %s%n", employee.getId());
            return employee;
        })
        .writer(list -> {
            for (Employee item : list) {
                System.out.println(item);
            }
        })
        .taskExecutor(new SimpleAsyncTaskExecutor("spring_batch"))
        .build();
}