[TYPO3-performance] Spreading HTTP request among multiple hostnames

[georg kuehnberger]

Martin Kutschker wrote:
> Mario Rimann schrieb:
>> Hi
>>
>> I recently played around with a new Firefox/Firebug add-on called "page
>> speed" [1] which is comparable to YSlow from Yahoo. The tool allows you
>> to generate reports regarding the performance of your website. And one
>> recommendation I saw was:
>>
>> ---
>> Parallelize downloads across hostnames
>> This page makes 40 parallelizable requests to www.domain.tld. Increase
>> download parallelization by distributing these requests across multiple
>> hostnames:
>> [list of 40 static files like css and images]
>> ---
>>
>> I know why this is recommended 
> 
> Could you elaborate or provide a link with an explanation? Unless there
> are "cheap" webservers handling only static content on the other side I
> don't see why my browser will be faster this way. Or is it simply
> because browsers will only make a limited number of requests to the same
> host?
> Masi

Masi, you guessed right:

Browsers DO limit the number of concurrent downloads from one Domain.
AFAIR 4 requests to one resolved IP are the usual concurrent max limit a 
broser would do. (I feel the yslow pages somewhere explained that 
browser-behavior - however dont find the link by now - sorry).

Beware though: adding hrefs pointing to too much hostnames would harm 
the clients real+percieved speed though;
reason: the OS-DNS lookup/resolution would take more time than the 
benefit of parallel delivery. (depending on the avail bandwidth thought) 
Avverage conclusion is/was not to use more than 2(-3) hostnames.

As we're talking (relatively) static files only here, I'd like however 
to recommend to:
a) timestamp/expire-header
b) minify
c) gzip
d) revers-proxy
all of those files, before considering a CDN - Your effort will it WILL 
pay off faster).
However as soon as a)-d) are done, or having discarding those options 
(for whatever constraints), CDNs definitely DO help support your task 
for a meaningful price/value.

regards georg