I write a web crawler.

The crawler has 2 steps:

1. get a html page
2. then parse the page

I want to use message queue to improve performance and throughput.

I think 2 scenarios:

scenario 1:

    structure: 
    urlProducer -> queue1 -> urlConsumer -> queue2 -> parserConsumer

urlProducer: get a target url and add it to queue1

urlConsumer: according to the job info, get the html page and add it to queue2

parserConsumer: according to the job info, parse the page

scenario 2:

    structure:
    urlProducer -> queue1 -> urlConsumer
    parserProducer-> queue2 -> parserConsumer

urlProducer : get a target url and add it to queue1

urlConsumer: according to the job info, get the html page and write it to db

parserProducer: get the html page from db and add it to queue2

parserConsumer: according to the job info, parse the page

There are multiple producers or consumers in each structure.

scenario1 likes a chaining call. It's difficult to find the point of problem, when occurring errors.

scenario2 decouples queue1 and queue2. It's easy to find the point of problem, when occurring errors.

I'm not sure the notion is correct.

Which one is the best scenario? Or other scenarios?

Thanks~