Spring Batch 5 면접: 파티셔닝, 청크, 장애 허용

// Java 21 기반 Spring Batch 5 잡 설정
@Configuration
public class BatchJobConfig {

    // JobRepository는 실행 메타데이터를 저장합니다
    // 잡 재시작과 모니터링을 가능하게 합니다
    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public BatchJobConfig(JobRepository jobRepository,
                          PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    // Job은 전체 배치 프로세스를 캡슐화합니다
    // 순차적으로 실행되는 하나 이상의 Step으로 구성됩니다
    @Bean
    public Job importUserJob(Step processUsersStep, Step cleanupStep) {
        return new JobBuilder("importUserJob", jobRepository)
                .start(processUsersStep)      // 메인 처리 Step
                .next(cleanupStep)             // 정리 Step
                .build();
    }

    // Step은 독립된 작업 단위를 나타냅니다
    // 두 가지 모델: Tasklet(단일 작업) 또는 Chunk(반복 처리)
    @Bean
    public Step processUsersStep(ItemReader<UserRecord> reader,
                                  ItemProcessor<UserRecord, User> processor,
                                  ItemWriter<User> writer) {
        return new StepBuilder("processUsersStep", jobRepository)
                .<UserRecord, User>chunk(100, transactionManager)  // 100건마다 커밋
                .reader(reader)       // 원본 데이터를 읽음
                .processor(processor) // 각 아이템을 변환
                .writer(writer)       // 100건 단위로 기록
                .build();
    }
}

// Tasklet: 반복 없는 단일 동작
@Component
public class CleanupTasklet implements Tasklet {

    private final Path tempDirectory = Path.of("/tmp/batch-work");

    @Override
    public RepeatStatus execute(StepContribution contribution,
                                 ChunkContext chunkContext) throws Exception {
        // 처리 과정에서 생긴 임시 파일을 모두 삭제
        try (var files = Files.walk(tempDirectory)) {
            files.filter(Files::isRegularFile)
                 .forEach(this::deleteQuietly);
        }

        // FINISHED는 tasklet이 작업을 완료했음을 의미
        // CONTINUABLE은 실행을 다시 시작(폴링에 유용)
        return RepeatStatus.FINISHED;
    }

    private void deleteQuietly(Path file) {
        try {
            Files.delete(file);
        } catch (IOException e) {
            // 로그만 남기고 계속 - 파일 하나로 잡을 실패시키지 않음
        }
    }
}

// 청크 처리: 대용량 처리
@Configuration
public class ChunkProcessingConfig {

    @Bean
    public Step processOrdersStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<OrderRecord> reader,
                                   ItemProcessor<OrderRecord, ProcessedOrder> processor,
                                   ItemWriter<ProcessedOrder> writer) {
        return new StepBuilder("processOrdersStep", jobRepository)
                // 500개 청크: 500건 읽기, 처리, 기록 후 커밋
                .<OrderRecord, ProcessedOrder>chunk(500, transactionManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                // 진행 상황 모니터링용 리스너
                .listener(new ChunkProgressListener())
                .build();
    }
}

// ItemReader: 한 번에 한 아이템씩 읽음
@StepScope
@Component
public class OrderItemReader implements ItemReader<OrderRecord> {

    // @StepScope: Step 실행마다 새 인스턴스
    // 동적인 잡 파라미터 주입을 가능하게 함
    @Value("#{jobParameters['startDate']}")
    private LocalDate startDate;

    private Iterator<OrderRecord> orderIterator;

    @BeforeStep
    public void initializeReader(StepExecution stepExecution) {
        // Step 시작 시 데이터 로딩
        List<OrderRecord> orders = fetchOrdersFromDate(startDate);
        this.orderIterator = orders.iterator();
    }

    @Override
    public OrderRecord read() {
        // 데이터 끝을 알리기 위해 null 반환
        // Spring Batch는 null을 받을 때까지 read()를 호출
        if (orderIterator.hasNext()) {
            return orderIterator.next();
        }
        return null;  // 데이터셋의 끝
    }

    private List<OrderRecord> fetchOrdersFromDate(LocalDate date) {
        // 데이터 소스에서 조회
        return List.of();  // 실제 구현
    }
}

// ItemProcessor: 각 아이템을 개별적으로 변환
@Component
public class OrderItemProcessor implements ItemProcessor<OrderRecord, ProcessedOrder> {

    private final PricingService pricingService;
    private final ValidationService validationService;

    public OrderItemProcessor(PricingService pricingService,
                               ValidationService validationService) {
        this.pricingService = pricingService;
        this.validationService = validationService;
    }

    @Override
    public ProcessedOrder process(OrderRecord item) {
        // null 반환은 아이템을 필터링(기록되지 않음)
        if (!validationService.isValid(item)) {
            return null;  // 아이템 필터링
        }

        // 비즈니스 변환
        BigDecimal finalPrice = pricingService.calculatePrice(item);

        return new ProcessedOrder(
                item.orderId(),
                item.customerId(),
                finalPrice,
                LocalDateTime.now()
        );
    }
}

// ItemWriter: 청크 전체를 한 번에 기록
@Component
public class OrderItemWriter implements ItemWriter<ProcessedOrder> {

    private final JdbcTemplate jdbcTemplate;

    public OrderItemWriter(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) {
        // 청크는 처리된 모든 아이템을 포함
        // 성능 최적화를 위한 배치 기록
        List<? extends ProcessedOrder> items = chunk.getItems();

        jdbcTemplate.batchUpdate(
                "INSERT INTO processed_orders (order_id, customer_id, final_price, processed_at) VALUES (?, ?, ?, ?)",
                items,
                items.size(),
                (ps, order) -> {
                    ps.setLong(1, order.orderId());
                    ps.setLong(2, order.customerId());
                    ps.setBigDecimal(3, order.finalPrice());
                    ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                }
        );
    }
}

// 청크 크기의 동적 설정
@Configuration
public class ChunkSizingConfig {

    // 대부분 상황에서 합리적인 기본값
    private static final int DEFAULT_CHUNK_SIZE = 100;

    // 가벼운 아이템(필드가 적은 경우)
    private static final int LIGHT_ITEMS_CHUNK_SIZE = 500;

    // 무거운 아이템(blob, 문서)
    private static final int HEAVY_ITEMS_CHUNK_SIZE = 25;

    @Bean
    public Step processLightDataStep(JobRepository jobRepository,
                                      PlatformTransactionManager txManager,
                                      ItemReader<LightRecord> reader,
                                      ItemWriter<LightRecord> writer) {
        return new StepBuilder("processLightDataStep", jobRepository)
                // 가벼운 아이템: 커밋 횟수를 줄이기 위해 더 큰 청크
                .<LightRecord, LightRecord>chunk(LIGHT_ITEMS_CHUNK_SIZE, txManager)
                .reader(reader)
                .writer(writer)
                .build();
    }

    @Bean
    public Step processDocumentsStep(JobRepository jobRepository,
                                      PlatformTransactionManager txManager,
                                      ItemReader<Document> reader,
                                      ItemProcessor<Document, ProcessedDocument> processor,
                                      ItemWriter<ProcessedDocument> writer) {
        return new StepBuilder("processDocumentsStep", jobRepository)
                // 무거운 문서: 메모리 사용을 제한하기 위해 작은 청크
                .<Document, ProcessedDocument>chunk(HEAVY_ITEMS_CHUNK_SIZE, txManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                .build();
    }
}

// 파티셔닝된 잡 설정
@Configuration
public class PartitionedJobConfig {

    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public PartitionedJobConfig(JobRepository jobRepository,
                                 PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    @Bean
    public Job partitionedImportJob(Step partitionedStep) {
        return new JobBuilder("partitionedImportJob", jobRepository)
                .start(partitionedStep)
                .build();
    }

    // 매니저 Step: 파티션을 조율
    @Bean
    public Step partitionedStep(Partitioner partitioner,
                                 Step workerStep,
                                 TaskExecutor taskExecutor) {
        return new StepBuilder("partitionedStep", jobRepository)
                // Partitioner를 통해 작업 분할
                .partitioner("workerStep", partitioner)
                // 각 파티션마다 실행할 Step
                .step(workerStep)
                // 8개 병렬 스레드
                .taskExecutor(taskExecutor)
                // 생성할 파티션 수
                .gridSize(8)
                .build();
    }

    // 병렬 실행을 위한 TaskExecutor
    @Bean
    public TaskExecutor batchTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(8);
        executor.setMaxPoolSize(16);
        executor.setQueueCapacity(50);
        executor.setThreadNamePrefix("batch-partition-");
        executor.initialize();
        return executor;
    }
}

// ID 범위 기반 Partitioner
@Component
public class RangePartitioner implements Partitioner {

    private final JdbcTemplate jdbcTemplate;

    public RangePartitioner(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public Map<String, ExecutionContext> partition(int gridSize) {
        // 데이터셋의 경계를 조회
        Long minId = jdbcTemplate.queryForObject(
                "SELECT MIN(id) FROM orders WHERE status = 'PENDING'", Long.class);
        Long maxId = jdbcTemplate.queryForObject(
                "SELECT MAX(id) FROM orders WHERE status = 'PENDING'", Long.class);

        if (minId == null || maxId == null) {
            return Map.of();  // 처리할 데이터 없음
        }

        // 각 파티션의 크기를 계산
        long range = (maxId - minId) / gridSize + 1;
        Map<String, ExecutionContext> partitions = new HashMap<>();

        for (int i = 0; i < gridSize; i++) {
            ExecutionContext context = new ExecutionContext();
            long start = minId + (i * range);
            long end = Math.min(start + range - 1, maxId);

            // 각 파티션이 자신의 경계를 받음
            context.putLong("minId", start);
            context.putLong("maxId", end);
            context.putInt("partitionNumber", i);

            partitions.put("partition" + i, context);
        }

        return partitions;
    }
}

// 메시징을 활용한 원격 파티셔닝 설정
@Configuration
public class RemotePartitioningConfig {

    @Bean
    public Step managerStep(JobRepository jobRepository,
                             Partitioner partitioner,
                             MessageChannelPartitionHandler partitionHandler) {
        return new StepBuilder("managerStep", jobRepository)
                .partitioner("workerStep", partitioner)
                // 원격 worker와 통신하는 핸들러
                .partitionHandler(partitionHandler)
                .build();
    }

    // PartitionHandler가 ExecutionContext를 worker로 전송
    @Bean
    public MessageChannelPartitionHandler partitionHandler(
            MessagingTemplate messagingTemplate,
            JobExplorer jobExplorer) {
        MessageChannelPartitionHandler handler = new MessageChannelPartitionHandler();
        handler.setStepName("workerStep");
        handler.setGridSize(4);
        handler.setMessagingOperations(messagingTemplate);
        handler.setJobExplorer(jobExplorer);
        // worker 완료 대기 타임아웃
        handler.setPollInterval(5000L);
        return handler;
    }
}

// worker 측 설정
@Configuration
public class WorkerConfiguration {

    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public WorkerConfiguration(JobRepository jobRepository,
                                PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    // worker는 파티션을 받아 Step을 실행
    @Bean
    public Step workerStep(ItemReader<OrderRecord> reader,
                            ItemProcessor<OrderRecord, ProcessedOrder> processor,
                            ItemWriter<ProcessedOrder> writer) {
        return new StepBuilder("workerStep", jobRepository)
                .<OrderRecord, ProcessedOrder>chunk(100, transactionManager)
                // 파티션 파라미터를 받기 위해 @StepScope 적용
                .reader(reader)
                .processor(processor)
                .writer(writer)
                .build();
    }

    // 파티션 경계를 사용하는 Reader
    @Bean
    @StepScope
    public JdbcCursorItemReader<OrderRecord> partitionedReader(
            DataSource dataSource,
            @Value("#{stepExecutionContext['minId']}") Long minId,
            @Value("#{stepExecutionContext['maxId']}") Long maxId) {
        return new JdbcCursorItemReaderBuilder<OrderRecord>()
                .name("partitionedOrderReader")
                .dataSource(dataSource)
                .sql("SELECT * FROM orders WHERE id BETWEEN ? AND ? AND status = 'PENDING'")
                .preparedStatementSetter(ps -> {
                    ps.setLong(1, minId);
                    ps.setLong(2, maxId);
                })
                .rowMapper(new OrderRecordRowMapper())
                .build();
    }
}

// 완전한 장애 허용 설정
@Configuration
public class FaultTolerantStepConfig {

    @Bean
    public Step faultTolerantStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<DataRecord> reader,
                                   ItemProcessor<DataRecord, ProcessedRecord> processor,
                                   ItemWriter<ProcessedRecord> writer,
                                   SkipPolicy customSkipPolicy) {
        return new StepBuilder("faultTolerantStep", jobRepository)
                .<DataRecord, ProcessedRecord>chunk(100, transactionManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                // 장애 허용 모드 활성화
                .faultTolerant()
                // SKIP: 검증 오류를 최대 10건까지 무시
                .skipLimit(10)
                .skip(ValidationException.class)
                .skip(DataIntegrityViolationException.class)
                // 일부 오류는 절대 스킵하지 않음
                .noSkip(FatalBatchException.class)
                // RETRY: 일시적 오류는 재시도
                .retryLimit(3)
                .retry(TransientDataAccessException.class)
                .retry(DeadlockLoserDataAccessException.class)
                // 재시도 사이의 지수적 백오프
                .backOffPolicy(exponentialBackOffPolicy())
                // 스킵을 로깅하는 리스너
                .listener(skipListener())
                .build();
    }

    @Bean
    public BackOffPolicy exponentialBackOffPolicy() {
        ExponentialBackOffPolicy policy = new ExponentialBackOffPolicy();
        policy.setInitialInterval(1000);  // 1초
        policy.setMultiplier(2.0);         // 재시도마다 두 배
        policy.setMaxInterval(10000);      // 최대 10초
        return policy;
    }

    @Bean
    public SkipListener<DataRecord, ProcessedRecord> skipListener() {
        return new SkipListener<>() {
            @Override
            public void onSkipInRead(Throwable t) {
                // 읽을 수 없는 아이템 로깅
            }

            @Override
            public void onSkipInProcess(DataRecord item, Throwable t) {
                // 처리에 실패한 아이템 로깅
            }

            @Override
            public void onSkipInWrite(ProcessedRecord item, Throwable t) {
                // 기록에 실패한 아이템 로깅
            }
        };
    }
}

// 고급 비즈니스 로직을 가진 SkipPolicy
@Component
public class AdaptiveSkipPolicy implements SkipPolicy {

    private static final int MAX_SKIP_COUNT = 100;
    private static final double MAX_SKIP_PERCENTAGE = 0.05;  // 최대 5%

    private final AtomicInteger totalProcessed = new AtomicInteger(0);
    private final AtomicInteger skipCount = new AtomicInteger(0);

    @Override
    public boolean shouldSkip(Throwable exception, long skipCountSoFar) {
        // 치명적 오류는 절대 스킵하지 않음
        if (exception instanceof FatalBatchException
                || exception instanceof OutOfMemoryError) {
            return false;
        }

        // 스킵 수의 절대 상한
        if (skipCountSoFar >= MAX_SKIP_COUNT) {
            return false;  // 잡 중단
        }

        // 비율 상한
        int total = totalProcessed.get();
        if (total > 1000) {  // 워밍업 후에만 적용
            double skipPercentage = (double) skipCountSoFar / total;
            if (skipPercentage > MAX_SKIP_PERCENTAGE) {
                return false;  // 비율적으로 오류가 너무 많음
            }
        }

        // 검증 및 데이터 오류 스킵
        return exception instanceof ValidationException
                || exception instanceof DataFormatException
                || exception instanceof IllegalArgumentException;
    }

    // 진행 추적을 위해 리스너에서 호출
    public void incrementProcessed() {
        totalProcessed.incrementAndGet();
    }
}

// 잡 재시작 관리 서비스
@Service
public class JobRestartService {

    private final JobLauncher jobLauncher;
    private final JobExplorer jobExplorer;
    private final JobRepository jobRepository;
    private final Job importJob;

    public JobRestartService(JobLauncher jobLauncher,
                              JobExplorer jobExplorer,
                              JobRepository jobRepository,
                              @Qualifier("importJob") Job importJob) {
        this.jobLauncher = jobLauncher;
        this.jobExplorer = jobExplorer;
        this.jobRepository = jobRepository;
        this.importJob = importJob;
    }

    public JobExecution restartFailedJob(Long jobExecutionId) throws Exception {
        // 실패한 실행 조회
        JobExecution failedExecution = jobExplorer.getJobExecution(jobExecutionId);

        if (failedExecution == null) {
            throw new IllegalArgumentException("Job execution not found: " + jobExecutionId);
        }

        // 잡 재시작 가능 여부 확인
        if (!failedExecution.getStatus().equals(BatchStatus.FAILED)) {
            throw new IllegalStateException("Only FAILED jobs can be restarted");
        }

        // 원래 실행과 동일한 파라미터 사용
        JobParameters originalParams = failedExecution.getJobParameters();

        // 잡 재실행 - 마지막 체크포인트에서 자동 재개
        return jobLauncher.run(importJob, originalParams);
    }

    public List<JobExecution> findRestartableJobs() {
        // 아직 재시작되지 않은 모든 FAILED 실행 나열
        return jobExplorer.findJobInstancesByJobName(importJob.getName(), 0, 100)
                .stream()
                .flatMap(instance -> jobExplorer.getJobExecutions(instance).stream())
                .filter(exec -> exec.getStatus() == BatchStatus.FAILED)
                .filter(this::isRestartable)
                .toList();
    }

    private boolean isRestartable(JobExecution execution) {
        // 더 최신의 성공 실행이 없는지 확인
        JobInstance instance = execution.getJobInstance();
        return jobExplorer.getJobExecutions(instance).stream()
                .noneMatch(exec -> exec.getStatus() == BatchStatus.COMPLETED);
    }
}

// 멀티 스레드 Step: 여러 스레드가 같은 데이터셋을 처리
@Configuration
public class MultiThreadedStepConfig {

    @Bean
    public Step multiThreadedStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<Record> reader,
                                   ItemProcessor<Record, ProcessedRecord> processor,
                                   ItemWriter<ProcessedRecord> writer,
                                   TaskExecutor taskExecutor) {
        return new StepBuilder("multiThreadedStep", jobRepository)
                .<Record, ProcessedRecord>chunk(100, transactionManager)
                // 주의: reader는 thread-safe해야 함
                .reader(synchronizedReader(reader))
                .processor(processor)
                .writer(writer)
                // 4개 스레드가 청크를 병렬 처리
                .taskExecutor(taskExecutor)
                .throttleLimit(4)
                .build();
    }

    // reader를 thread-safe로 만드는 래퍼
    private ItemReader<Record> synchronizedReader(ItemReader<Record> reader) {
        SynchronizedItemStreamReader<Record> syncReader = new SynchronizedItemStreamReader<>();
        syncReader.setDelegate((ItemStreamReader<Record>) reader);
        return syncReader;
    }
}

// 독립 Step을 병렬 실행
@Configuration
public class ParallelStepsConfig {

    @Bean
    public Job parallelJob(JobRepository jobRepository,
                            Step loadCustomersStep,
                            Step loadProductsStep,
                            Step loadOrdersStep,
                            Step processDataStep) {
        // 병렬 플로우: customers와 products를 동시에 적재
        Flow loadCustomersFlow = new FlowBuilder<Flow>("loadCustomersFlow")
                .start(loadCustomersStep)
                .build();

        Flow loadProductsFlow = new FlowBuilder<Flow>("loadProductsFlow")
                .start(loadProductsStep)
                .build();

        Flow loadOrdersFlow = new FlowBuilder<Flow>("loadOrdersFlow")
                .start(loadOrdersStep)
                .build();

        // Split이 플로우를 병렬 실행
        return new JobBuilder("parallelJob", jobRepository)
                .start(new FlowBuilder<Flow>("parallelLoadFlow")
                        .split(new SimpleAsyncTaskExecutor())
                        .add(loadCustomersFlow, loadProductsFlow, loadOrdersFlow)
                        .build())
                // 병렬 적재 후 순차 처리
                .next(processDataStep)
                .build()
                .build();
    }
}

// Micrometer 기반 모니터링 설정
@Configuration
public class BatchMetricsConfig {

    private final MeterRegistry meterRegistry;

    public BatchMetricsConfig(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
    }

    @Bean
    public JobExecutionListener metricsJobListener() {
        return new JobExecutionListener() {

            private Timer.Sample jobTimer;

            @Override
            public void beforeJob(JobExecution jobExecution) {
                // 잡 소요 시간 타이머 시작
                jobTimer = Timer.start(meterRegistry);
                Counter.builder("batch.job.started")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .register(meterRegistry)
                        .increment();
            }

            @Override
            public void afterJob(JobExecution jobExecution) {
                // 총 소요 시간 기록
                jobTimer.stop(Timer.builder("batch.job.duration")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .tag("status", jobExecution.getStatus().toString())
                        .register(meterRegistry));

                // 상태별 잡 카운터
                Counter.builder("batch.job.completed")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .tag("status", jobExecution.getStatus().toString())
                        .register(meterRegistry)
                        .increment();
            }
        };
    }

    @Bean
    public StepExecutionListener metricsStepListener() {
        return new StepExecutionListener() {

            @Override
            public void afterStep(StepExecution stepExecution) {
                String jobName = stepExecution.getJobExecution().getJobInstance().getJobName();
                String stepName = stepExecution.getStepName();

                // 처리량 메트릭
                Gauge.builder("batch.step.read.count", stepExecution, StepExecution::getReadCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                Gauge.builder("batch.step.write.count", stepExecution, StepExecution::getWriteCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                Gauge.builder("batch.step.skip.count", stepExecution, StepExecution::getSkipCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                return null;
            }
        };
    }
}

// 부하를 실제로 균형 잡는 Partitioner
@Component
public class BalancedPartitioner implements Partitioner {

    private final JdbcTemplate jdbcTemplate;

    public BalancedPartitioner(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public Map<String, ExecutionContext> partition(int gridSize) {
        // 처리할 전체 아이템 수 계산
        Integer totalCount = jdbcTemplate.queryForObject(
                "SELECT COUNT(*) FROM orders WHERE status = 'PENDING'", Integer.class);

        if (totalCount == null || totalCount == 0) {
            return Map.of();
        }

        // 파티션당 목표 크기 계산
        int itemsPerPartition = (int) Math.ceil((double) totalCount / gridSize);

        Map<String, ExecutionContext> partitions = new HashMap<>();

        // 균형 잡힌 파티션을 위해 OFFSET/LIMIT 사용
        // 범위 분할보다 비용은 크지만 균형을 보장
        for (int i = 0; i < gridSize; i++) {
            ExecutionContext context = new ExecutionContext();
            context.putInt("offset", i * itemsPerPartition);
            context.putInt("limit", itemsPerPartition);
            context.putInt("partitionNumber", i);

            partitions.put("partition" + i, context);
        }

        return partitions;
    }
}

// OffsetBasedReader.java
// 오프셋 기반 파티셔닝과 호환되는 Reader
@StepScope
@Component
public class OffsetBasedReader implements ItemReader<OrderRecord>, ItemStream {

    private final JdbcTemplate jdbcTemplate;
    private Iterator<OrderRecord> iterator;

    @Value("#{stepExecutionContext['offset']}")
    private int offset;

    @Value("#{stepExecutionContext['limit']}")
    private int limit;

    public OffsetBasedReader(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void open(ExecutionContext executionContext) {
        // 이 파티션에 할당된 부분만 정확히 로딩
        List<OrderRecord> records = jdbcTemplate.query(
                "SELECT * FROM orders WHERE status = 'PENDING' ORDER BY id LIMIT ? OFFSET ?",
                new OrderRecordRowMapper(),
                limit, offset
        );
        this.iterator = records.iterator();
    }

    @Override
    public OrderRecord read() {
        return iterator.hasNext() ? iterator.next() : null;
    }

    @Override
    public void update(ExecutionContext executionContext) {
        // 필요 시 재시작용 상태 저장
    }

    @Override
    public void close() {
        // 정리
    }
}

// 잡 간 의존성 관리
@Service
public class JobDependencyService {

    private final JobExplorer jobExplorer;
    private final JobLauncher jobLauncher;
    private final Map<String, Job> jobs;

    public JobDependencyService(JobExplorer jobExplorer,
                                  JobLauncher jobLauncher,
                                  Map<String, Job> jobs) {
        this.jobExplorer = jobExplorer;
        this.jobLauncher = jobLauncher;
        this.jobs = jobs;
    }

    public JobExecution runWithDependencies(String jobName,
                                             JobParameters params,
                                             List<String> dependsOn) throws Exception {
        // 모든 의존성이 성공했는지 확인
        for (String dependency : dependsOn) {
            if (!hasSuccessfulExecution(dependency, params)) {
                throw new JobExecutionException(
                        "Dependency not satisfied: " + dependency);
            }
        }

        Job job = jobs.get(jobName);
        if (job == null) {
            throw new IllegalArgumentException("Unknown job: " + jobName);
        }

        return jobLauncher.run(job, params);
    }

    private boolean hasSuccessfulExecution(String jobName, JobParameters params) {
        // 동일한 비즈니스 파라미터로 COMPLETED인 실행 검색
        return jobExplorer.findJobInstancesByJobName(jobName, 0, 1)
                .stream()
                .flatMap(instance -> jobExplorer.getJobExecutions(instance).stream())
                .filter(exec -> exec.getStatus() == BatchStatus.COMPLETED)
                .anyMatch(exec -> matchesBusinessParams(exec.getJobParameters(), params));
    }

    private boolean matchesBusinessParams(JobParameters actual, JobParameters expected) {
        // 비즈니스 파라미터 비교(실행 타임스탬프 무시)
        String actualDate = actual.getString("businessDate");
        String expectedDate = expected.getString("businessDate");
        return Objects.equals(actualDate, expectedDate);
    }
}

// 프로세서 유닛 테스트
@ExtendWith(MockitoExtension.class)
class OrderProcessorTest {

    @Mock
    private PricingService pricingService;

    @Mock
    private ValidationService validationService;

    @InjectMocks
    private OrderItemProcessor processor;

    @Test
    void shouldProcessValidOrder() {
        // Given
        OrderRecord input = new OrderRecord(1L, 100L, BigDecimal.TEN);
        when(validationService.isValid(input)).thenReturn(true);
        when(pricingService.calculatePrice(input)).thenReturn(new BigDecimal("12.50"));

        // When
        ProcessedOrder result = processor.process(input);

        // Then
        assertThat(result).isNotNull();
        assertThat(result.finalPrice()).isEqualTo(new BigDecimal("12.50"));
    }

    @Test
    void shouldFilterInvalidOrder() {
        // Given
        OrderRecord input = new OrderRecord(1L, 100L, BigDecimal.TEN);
        when(validationService.isValid(input)).thenReturn(false);

        // When
        ProcessedOrder result = processor.process(input);

        // Then - null은 필터링됨을 의미
        assertThat(result).isNull();
        verify(pricingService, never()).calculatePrice(any());
    }
}

// 잡 전체에 대한 통합 테스트
@SpringBatchTest
@SpringBootTest
@ActiveProfiles("test")
class ImportJobIntegrationTest {

    @Autowired
    private JobLauncherTestUtils jobLauncherTestUtils;

    @Autowired
    private JobRepositoryTestUtils jobRepositoryTestUtils;

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @BeforeEach
    void setup() {
        // 테스트 사이의 메타데이터 정리
        jobRepositoryTestUtils.removeJobExecutions();
        // 테스트 데이터 초기화
        jdbcTemplate.execute("DELETE FROM processed_orders");
        jdbcTemplate.execute("DELETE FROM orders");
    }

    @Test
    void shouldCompleteJobSuccessfully() throws Exception {
        // Given - 테스트 데이터
        insertTestOrders(100);

        // When
        JobParameters params = new JobParametersBuilder()
                .addLocalDate("businessDate", LocalDate.now())
                .addLong("run.id", System.currentTimeMillis())
                .toJobParameters();

        JobExecution execution = jobLauncherTestUtils.launchJob(params);

        // Then
        assertThat(execution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
        assertThat(countProcessedOrders()).isEqualTo(100);
    }

    @Test
    void shouldHandleEmptyDataset() throws Exception {
        // Given - 데이터 없음

        // When
        JobExecution execution = jobLauncherTestUtils.launchJob();

        // Then - 데이터가 없어도 잡은 성공
        assertThat(execution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
    }

    @Test
    void shouldRestartFromFailurePoint() throws Exception {
        // Given - 처리 도중의 오류 시뮬레이션
        insertTestOrders(100);
        insertPoisonOrder(50);  // 오류 발생

        // When - 첫 실행 실패
        JobExecution firstExecution = jobLauncherTestUtils.launchJob();
        assertThat(firstExecution.getStatus()).isEqualTo(BatchStatus.FAILED);

        // 데이터 수정
        removePoisonOrder(50);

        // When - 재시작
        JobExecution restartExecution = jobLauncherTestUtils.launchJob(
                firstExecution.getJobParameters());

        // Then - 실패 지점부터 재개
        assertThat(restartExecution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
    }

    private void insertTestOrders(int count) {
        for (int i = 1; i <= count; i++) {
            jdbcTemplate.update(
                    "INSERT INTO orders (id, customer_id, amount, status) VALUES (?, ?, ?, 'PENDING')",
                    i, i * 10, BigDecimal.valueOf(i * 10));
        }
    }

    private int countProcessedOrders() {
        return jdbcTemplate.queryForObject(
                "SELECT COUNT(*) FROM processed_orders", Integer.class);
    }
}

// 대용량을 위한 최적화된 Writer
@Component
public class OptimizedJdbcWriter implements ItemWriter<ProcessedOrder> {

    private final JdbcTemplate jdbcTemplate;
    private final DataSource dataSource;

    public OptimizedJdbcWriter(JdbcTemplate jdbcTemplate, DataSource dataSource) {
        this.jdbcTemplate = jdbcTemplate;
        this.dataSource = dataSource;
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) throws Exception {
        List<? extends ProcessedOrder> items = chunk.getItems();

        if (items.isEmpty()) {
            return;
        }

        // 배치와 함께 PreparedStatement 사용
        try (Connection connection = dataSource.getConnection();
             PreparedStatement ps = connection.prepareStatement(
                     "INSERT INTO processed_orders (order_id, customer_id, final_price, processed_at) " +
                             "VALUES (?, ?, ?, ?)")) {

            for (ProcessedOrder order : items) {
                ps.setLong(1, order.orderId());
                ps.setLong(2, order.customerId());
                ps.setBigDecimal(3, order.finalPrice());
                ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                ps.addBatch();
            }

            // 모든 INSERT를 한 번의 네트워크 호출로 실행
            ps.executeBatch();
        }
    }
}

// StagingTableWriter.java
// 초대용량을 위한 스테이징 테이블 패턴
@Component
public class StagingTableWriter implements ItemWriter<ProcessedOrder>, StepExecutionListener {

    private final JdbcTemplate jdbcTemplate;
    private String stagingTable;

    public StagingTableWriter(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void beforeStep(StepExecution stepExecution) {
        // 이 Step을 위한 임시 테이블 생성
        stagingTable = "staging_orders_" + stepExecution.getId();
        jdbcTemplate.execute(
                "CREATE TEMP TABLE " + stagingTable + " (LIKE processed_orders INCLUDING ALL)");
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) {
        // 스테이징 테이블에 기록(FK 제약 없음)
        String sql = "INSERT INTO " + stagingTable +
                " (order_id, customer_id, final_price, processed_at) VALUES (?, ?, ?, ?)";

        jdbcTemplate.batchUpdate(sql, chunk.getItems(), chunk.size(),
                (ps, order) -> {
                    ps.setLong(1, order.orderId());
                    ps.setLong(2, order.customerId());
                    ps.setBigDecimal(3, order.finalPrice());
                    ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                });
    }

    @Override
    public ExitStatus afterStep(StepExecution stepExecution) {
        if (stepExecution.getStatus() == BatchStatus.COMPLETED) {
            // 최종 테이블로 일괄 복사
            jdbcTemplate.execute(
                    "INSERT INTO processed_orders SELECT * FROM " + stagingTable);
        }
        // 스테이징 테이블 정리
        jdbcTemplate.execute("DROP TABLE IF EXISTS " + stagingTable);
        return stepExecution.getExitStatus();
    }
}