Possible memory leak?

Maxim Dounin mdounin at mdounin.ru
Wed Mar 27 20:26:00 UTC 2019


On Wed, Mar 27, 2019 at 02:54:41PM -0400, wkbrad wrote:

> Combine all of that with the fact that this issue happens on all systems and
> that the direct competitor doesn't have this issue, that makes me think this
> is something that Nginx needs to address directly.

If by "direct competitor" you mean Apache you've previously 
mentioned in this thread, note that:

- Apache doesn't try to provide a safe configuration reload, and 
  will be in an unusable state if something goes wrong while 
loading the new configuration (not to mention that Apache can't do 
a configuration reload while processing ongoing requests at the 
same time, and instead pauses all processing till reload is 
complete).  This is not something nginx can afford, and hence we 
do it differently.  While our approach may need more memory, this 
is something we are ready to pay to make sure no requests will be 

- And, really, nginx and Apache are not direct competitors.  If 
  Apache works for you - use it, it is a reputable server we all 
love and use or used in the past.  Though it doesn't scale good 
enough to thousands of connections, and that's why nginx was 
written in the first place.  And it also cannot handle upgrades 
and configuration reloads seamlessly, so it cannot be used as a 
frontend server on loaded sites unless you have a way to direct 
traffic to a different server.  Nevertheless, even on loaded sites 
Apache can be (and often is) used as a backend server behind 
nginx, and it does this just fine.

What nginx does to keep configuration reloads seamless certainly 
require additional resources, but this is something we do for a 
good reason.  And this particular problem is relatively easy to 
mitigate by keeping a configuration small (the other side of the 
problem is that you anyway need about 2x memory on the server, 
including various client-related buffers, so nginx will be able to 
start two sets of worker processes during the configuration 
reload, and this is something you can't mitigate at all; the good 
part is that this memory is not wasted but used for page cache 
between reloads).  Also, if you really think this is a major 
problem, you may want to start working on improving system 
allocators to handle this better, it is something certainly 

Maxim Dounin

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