Changes with nginx 1.9.13                                        29 Mar
2016
*) Change: non-idempotent requests (POST, LOCK, PATCH) are no longer
   passed to the next server by default if a request has been sent 
to a
backend; the “non_idempotent” parameter of the
“proxy_next_upstream”
directive explicitly allows retrying such requests.
*) Feature: the ngx_http_perl_module can be built dynamically.
*) Feature: UDP support in the stream module.
*) Feature: the "aio_write" directive.
*) Feature: now cache manager monitors number of elements in caches 
and
tries to avoid cache keys zone overflows.
*) Bugfix: "task already active" and "second aio post" alerts might
   appear in logs when using the "sendfile" and "aio" directives 
with
subrequests.
*) Bugfix: "zero size buf in output" alerts might appear in logs if
   caching was used and a client closed a connection prematurely.
*) Bugfix: connections with clients might be closed needlessly if
   caching was used.
   Thanks to Justin Li.
*) Bugfix: nginx might hog CPU if the "sendfile" directive was used 
on
Linux or Solaris and a file being sent was changed during
sending.
*) Bugfix: connections might hang when using the "sendfile" and "aio
   threads" directives.
*) Bugfix: in the "proxy_pass", "fastcgi_pass", "scgi_pass", and
   "uwsgi_pass" directives when using variables.
   Thanks to Piotr S..
*) Bugfix: in the ngx_http_sub_filter_module.
*) Bugfix: if an error occurred in a cached backend connection, the
   request was passed to the next server regardless of the
   proxy_next_upstream directive.
*) Bugfix: "CreateFile() failed" errors when creating temporary 
files on
Windows.
–
Maxim D.
http://nginx.org/