Upstream: different header lists for cached and uncached requests. The upstream modules remove and alter a number of client headers before sending the request to upstream. This set of headers is smaller or even empty when cache is disabled. It's still possible that a request in a cache-enabled location is uncached, for example, if cache entry counter is below min_uses. In this case it's better to alter a smaller set of headers and pass more client headers to backend unchanged. One of the benefits is enabling server-side byte ranges in such requests.

ngx_addon_name=ngx_mysql

HTTP_MODULES="$HTTP_MODULES ngx_http_mysql_test_module"

HTTP_INCS="$HTTP_INCS $ngx_addon_dir"
HTTP_DEPS="$HTTP_DEPS $ngx_addon_dir/ngx_mysql.h"
#CORE_LIBS="$CORE_LIBS -lmd"

USE_SHA1=YES

NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_mysql.c"
NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_mysql_test.c"