Concurrent AJAX file upload LIMIT

问题:

I'm doing multiple file uploader to upload my files by using XMLHttp 2. When i'm doing this, if i upload the files one by one (by sending a file through an ajax request and waiting it to complete before sending the next and so on), the uploader works well. But when i upload multiple files by using concurrent ajax requests to upload multiple files concurrently, the browser hangs down. Here is the performance comparison,

So is there any maximum limit for UPLOAD FILE SIZE or NUMBER OF AJAX REQUESTS that the browser can handle concurrently?

Note: That red numbers shows the total upload time in that the Firefox(using firebug) consumes to upload all the files. In parallel upload, since all uploads happening concurrently, i took the time consumed by the largest file which ended at last.

回答1:

There's no theoretical maximum for the number of concurrent uploads (unless the browser builders put one in explicitly).

However, in practice, upload speed performance drops significantly after two or three concurrent uploads due to bandwidth choking, with the exception of very low latency whereby the tcp window limits the maximum speed of a single upload.

I would recommend setting a concurrency limit of 2, especially if you're providing this to external users whose bandwidth may vary. Alternatively, you could do speed benchmarking as well, adapting the concurrency level based on measured upload performance.