cache-file-descriptors.conf: new feature which greatly speeds up performance on very busy production sites

nginx/conf/cache-file-descriptors.conf

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+# This tells Nginx to cache open file handles, "not found" errors, metadata about files and their permissions, etc.
+#
+# The upside of this is that Nginx can immediately begin sending data when a popular file is requested,
+# and will also know to immediately send a 404 if a file is missing on disk, and so on.
+#
+# However, it also means that the server won't react immediately to changes on disk, which may be undesirable.
+#
+# In the below configuration, inactive files are released from the cache after 20 seconds, whereas
+# active (recently requested) files are re-validated every 30 seconds.
+#
+# Descriptors will not be cached unless they are used at least 2 times within 20 seconds (the inactive time).
+#
+# A maximum of the 1000 most recently used file descriptors can be cached at any time.
+#
+# Production servers with stable file collections will definitely want to enable the cache.
+open_file_cache          max=1000 inactive=20s;
+open_file_cache_valid    30s;
+open_file_cache_min_uses 2;
+open_file_cache_errors   on;