New directives: proxy_cache_lock on/off, proxy_cache_lock_timeout. With
proxy_cache_lock set to on, only one request will be allowed to go to
upstream for a particular cache item. Others will wait for a response
to appear in cache (or cache lock released) up to proxy_cache_lock_timeout.
Waiting requests will recheck if they have cached response ready (or are
allowed to run) every 500ms.
Note: we intentionally don't intercept NGX_DECLINED possibly returned by
ngx_http_file_cache_read(). This needs more work (possibly safe, but needs
further investigation). Anyway, it's exceptional situation.
Note: probably there should be a way to disable caching of responses
if there is already one request fetching resource to cache (without waiting
at all). Two possible ways include another cache lock option ("no_cache")
or using proxy_no_cache with some supplied variable.
Note: probably there should be a way to lock updating requests as well. For
now "proxy_cache_use_stale updating" is available.
It's possible that configured limit_rate will permit more bytes per
single operation than sendfile_max_chunk. To protect disk from takeover
by a single client it is necessary to apply sendfile_max_chunk as a limit
regardless of configured limit_rate.
See here for report (in Russian):
http://mailman.nginx.org/pipermail/nginx-ru/2010-March/032806.html
If proxy_pass was used with variables and there was no URI component,
nginx always used unparsed URI. This isn't consistent with "no variables"
case, where e.g. rewrites are applied even if there is no URI component.
Fix is to use the same logic in both cases, i.e. only use unparsed URI if
it's valid and request is the main one.
This resolves issue with try_files (see ticket #70), configuration like
location / { try_files $uri /index.php; }
location /index.php { proxy_pass http://backend; }
caused nginx to use original request uri in a request to a backend.
Historically, not clearing of the r->valid_unparsed_uri on internal redirect
was a feature: it allowed to pass the same request to (another) upstream
server via error_page redirection. Since then named locations appeared
though, and it's time to start resetting r->valid_unparsed_uri on internal
redirects. Configurations still using this feature should be converted
to use named locations instead.
Patch by Lanshun Zhou.
The SCGI specification doesn't specify format of the response, and assuming
CGI specs should be used there is no reason to complain. RFC 3875
explicitly states that "A Status header field is optional, and status
200 'OK' is assumed if it is omitted".
The r->http_version is a version of client's request, and modules must
not set it unless they are really willing to downgrade protocol version
used for a response (i.e. to HTTP/0.9 if no response headers are available).
In neither case r->http_version may be upgraded.
The former code downgraded response from HTTP/1.1 to HTTP/1.0 for no reason,
causing various problems (see ticket #66). It was also possible that
HTTP/0.9 requests were upgraded to HTTP/1.0.
There have been multiple reports of cases where a real locked entry was
removed, resulting in a segmentation fault later in a worker which locked
the entry. It looks like default inactive timeout isn't enough in real
life.
For now just ignore such locked entries, and move them to the top of the
inactive queue to allow processing of other entries.
There are two possible situations which can lead to this: response was
cached with bigger proxy_buffer_size value (and nginx was restared since
then, i.e. shared memory zone content was lost), or due to the race in
the cache update code (see [1]) we've end up with fcn->body_start from
a different response stored in shared memory zone.
[1] http://mailman.nginx.org/pipermail/nginx-devel/2011-September/001287.html
The ngx_http_cache() and ngx_http_no_cache_set_slot() functions were replaced
by ngx_http_test_predicates() and ngx_http_set_predicate_slot() in 0.8.46 and
no longer used since then.
FreeBSD kernel checks headers/trailers pointer against NULL, not
corresponding count. Passing NULL if there are no headers/trailers
helps to avoid unneeded work in kernel, as well as unexpected 0 bytes
GIO in traces.
haven't been sent to a client.
The ngx_http_variable_headers() and ngx_http_variable_unknown_header() functions
did not ignore response header entries with zero "hash" field.
Thanks to Yichun Zhang (agentzh).
