id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
1880	nginx should bypass cache if worker failed to allocate node in cache keys zone	keyolk@…		"Copied from https://trac.nginx.org/nginx/ticket/1824

Using http file cache.
Seems that if a worker failed to allocate node in cache keys,
then it tries forcely expire cache and allocate node again.
But at the same time if another worker takes the cache first,
the worker will return 500 error with below log
""could not allocate node in cache keys zone""

I think it would be better just bypassing cache and read data from upstreams, instead of returning 500 error.
I tested simple patch below,
Not sure whether it proper approach
but seems it mitigates symptom.

{{{
diff -r e7181cfe9212 src/http/ngx_http_file_cache.c
--- a/src/http/ngx_http_file_cache.c    Tue Jul 23 15:01:47 2019 +0300
+++ b/src/http/ngx_http_file_cache.c    Tue Jul 30 17:07:51 2019 +0900
@@ -299,11 +299,7 @@
     ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                    ""http file cache exists: %i e:%d"", rc, c->exists);

-    if (rc == NGX_ERROR) {
-        return rc;
-    }
-
-    if (rc == NGX_AGAIN) {
+    if (rc == NGX_AGAIN || rc == NGX_ERROR) {
         return NGX_HTTP_CACHE_SCARCE;
     }
}}}"	defect	closed	minor		other	1.17.x	duplicate	http file cache		Linux my 4.19.45-nx #500 SMP Thu May 23 00:56:30 KST 2019 x86_64 GNU/Linux	nginx version: nginx/1.17.2 built by gcc 4.8.5 20150623 (Red Hat 4.8.5-36) (GCC) built with OpenSSL 1.0.2k-fips 26 Jan 2017 TLS SNI support enabled configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib64/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-compat --with-file-aio --with-threads --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_flv_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_random_index_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-mail_ssl_module --with-stream --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-cc-opt='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC' --with-ld-opt='-Wl,-z,relro -Wl,-z,now -pie' --with-debug