question about proxy_buffers

[merlin corey]

2009/6/11 Jérôme Loyet <jerome at loyet.net>:
> 2009/6/10 merlin corey <merlincorey at dc949.org>:
>> I'm not Igor so I cannot be totally sure, but my understanding of it
>> has always been 1- requests to the backend can use only one buffer and
>> the response gets buffered to disk.  As such, I generally start out
>> sites with log level info (might be too low) and try to tune down
>> requests getting buffered if at all possible.  I also try to stick
>> with magic numbers good for the architecture (so 8 and 16 based,
>> generally).
>>
> Thx for the answer merlin,
>
> I did some test. The request I make to nginx is proxied to the
> backend. There is only one request made at the same time.
> I request a 5Mo file.
>
> First: with minimum buffers:
> proxy_buffers 2 4k;
>
> I have this in the log: 2009/06/11 19:40:05 [warn] 24607#0: *104 an
> upstream response is buffered to a temporary file
> /LIBRE/nginx/proxy_temp/0000000000 while reading upstream, ....
>
> Then I set 10 buffers of 1Mo:
> proxy_buffers 10 1m;
> and nothing appears in logs.
>
> This tells me that a request can use more than one buffer.
>
> I'll set up small buffers but a large number:
> proxy_buffers 2048 8k;
>
> Is it too much ?
>
>>
>> 2009/6/9 Jérôme Loyet <jerome at loyet.net>:
>>> Hi all,
>>>
>>> I'm not sure how proxy_buffers are used.
>>>
>>> 1- requests to the backend can use only one buffer. If the reponse is
>>> bigger than one buffer, some part of the response is buffered to disk.
>>> 2- requests to the backen can use multiple buffers. If the response is
>>> bigger than on buffer, nginx will use more buffers (if available of
>>> course).
>>>
>>> So depending on the answer, I would use :
>>> 1- big buffers so that 80% of the requests can feet in on buffer. And
>>> enough buffers so that 80% of the requests can be buffered
>>> 2- small buffers and a lots of buffers
>>>
>>> don't know what to use :) any clue ?
>>>
>>> thx
>>> ++ jerome
>>>
>>>
>>
>>
>
>

Nice work!  I guess for figuring out if it is too much you need to
look at your system and determine if it will be using too much memory,
but I would bet you can easily handle the 16MB + whatever structure
overhead for those 2048 buffers.  Possibly other factors like paging
and caching (on CPU level) might come into play, too, but probably not
at our (human) granuality.