How to optimize my performances using FlatFileItemReader and Asynchronous Processors

I have a simple csv file with ~400,000 line(one column only) It takes me alot of time to read the records and process them

the processor validating records against couchbase

the writer - writing into remote topic Takes me around 30 mins. thats insane.

I read that flatfileItemreader is not thread safe. so my chunk value is 1.

I read the Asynchronous processing could assist. but I cant see any improvements.

Thats my code:

@Configuration
@EnableBatchProcessing
public class NotificationFileProcessUploadedFileJob {


    @Value("${expected.snid.header}")
    public String snidHeader;

    @Value("${num.of.processing.chunks.per.file}")
    public int numOfProcessingChunksPerFile;

    @Autowired
    private InfrastructureConfigurationConfig infrastructureConfigurationConfig;

    private static final String OVERRIDDEN_BY_EXPRESSION = null;


    @Inject
    private JobBuilderFactory jobs;

    @Inject
    private StepBuilderFactory stepBuilderFactory;

    @Inject
    ExecutionContextPromotionListener executionContextPromotionListener;


    @Bean
    public Job processUploadedFileJob() throws Exception {
        return this.jobs.get("processUploadedFileJob").start((processSnidUploadedFileStep())).build();

    }

    @Bean
    public Step processSnidUploadedFileStep() {
        return stepBuilderFactory.get("processSnidFileStep")
                .<PushItemDTO, PushItemDTO>chunk(numOfProcessingChunksPerFile)
                .reader(snidFileReader(OVERRIDDEN_BY_EXPRESSION))
                .processor(asyncItemProcessor())
                .writer(asyncItemWriter())
            //    .throttleLimit(20)
             //   .taskJobExecutor(infrastructureConfigurationConfig.taskJobExecutor())


                        //     .faultTolerant()
                        //   .skipLimit(10) //default is set to 0
                        //     .skip(MySQLIntegrityConstraintViolationException.class)
                .build();
    }

    @Inject
    ItemWriter writer;

    @Bean
    public AsyncItemWriter asyncItemWriter() {
        AsyncItemWriter asyncItemWriter=new AsyncItemWriter();
        asyncItemWriter.setDelegate(writer);
        return asyncItemWriter;
    }


    @Bean
    @Scope(value = "step", proxyMode = ScopedProxyMode.INTERFACES)
    public ItemStreamReader<PushItemDTO> snidFileReader(@Value("#{jobParameters[filePath]}") String filePath) {
        FlatFileItemReader<PushItemDTO> itemReader = new FlatFileItemReader<PushItemDTO>();
        itemReader.setLineMapper(snidLineMapper());
        itemReader.setLinesToSkip(1);
        itemReader.setResource(new FileSystemResource(filePath));
        return itemReader;
    }


    @Bean
    public AsyncItemProcessor asyncItemProcessor() {

        AsyncItemProcessor<PushItemDTO, PushItemDTO> asyncItemProcessor = new AsyncItemProcessor();

        asyncItemProcessor.setDelegate(processor(OVERRIDDEN_BY_EXPRESSION, OVERRIDDEN_BY_EXPRESSION, OVERRIDDEN_BY_EXPRESSION,
                OVERRIDDEN_BY_EXPRESSION, OVERRIDDEN_BY_EXPRESSION, OVERRIDDEN_BY_EXPRESSION, OVERRIDDEN_BY_EXPRESSION));
        asyncItemProcessor.setTaskExecutor(infrastructureConfigurationConfig.taskProcessingExecutor());

        return asyncItemProcessor;

    }

    @Scope(value = "step", proxyMode = ScopedProxyMode.INTERFACES)
    @Bean
    public ItemProcessor<PushItemDTO, PushItemDTO> processor(@Value("#{jobParameters[pushMessage]}") String pushMessage,
                                                             @Value("#{jobParameters[jobId]}") String jobId,
                                                             @Value("#{jobParameters[taskId]}") String taskId,
                                                             @Value("#{jobParameters[refId]}") String refId,
                                                             @Value("#{jobParameters[url]}") String url,
                                                             @Value("#{jobParameters[targetType]}") String targetType,
                                                             @Value("#{jobParameters[gameType]}") String gameType) {
        return new PushItemProcessor(pushMessage, jobId, taskId, refId, url, targetType, gameType);
    }

    @Bean
    public LineMapper<PushItemDTO> snidLineMapper() {
        DefaultLineMapper<PushItemDTO> lineMapper = new DefaultLineMapper<PushItemDTO>();
        DelimitedLineTokenizer lineTokenizer = new DelimitedLineTokenizer();
        lineTokenizer.setDelimiter(",");
        lineTokenizer.setStrict(true);
        lineTokenizer.setStrict(true);
        String[] splittedHeader = snidHeader.split(",");
        lineTokenizer.setNames(splittedHeader);
        BeanWrapperFieldSetMapper<PushItemDTO> fieldSetMapper = new BeanWrapperFieldSetMapper<PushItemDTO>();
        fieldSetMapper.setTargetType(PushItemDTO.class);

        lineMapper.setLineTokenizer(lineTokenizer);
        lineMapper.setFieldSetMapper(new PushItemFieldSetMapper());
        return lineMapper;
    }
}


 @Bean
    @Override
    public SimpleAsyncTaskExecutor taskProcessingExecutor() {
        SimpleAsyncTaskExecutor simpleAsyncTaskExecutor = new SimpleAsyncTaskExecutor();
        simpleAsyncTaskExecutor.setConcurrencyLimit(300);
        return simpleAsyncTaskExecutor;
    }

How do you think I could improve the processing performances and make them faster? thank you