Вопрос по дебагу

[CoDDoC]

Доброго времени суток!
Подскажите, плиз, где можно почитать нормальную документацию про сообщения в дебаг логе.
Перерыл весь гугол, ничего толком нет. Честно, надоело играть в угадайку.

Например, что означают такие записи в режиме debug_http:

1. 2017/11/13 07:41:37 [debug] 624#0: *244736 rewrite phase: 3
    2017/11/13 07:41:37 [debug] 624#0: *244736 post rewrite phase: 4
    2017/11/13 07:41:37 [debug] 624#0: *244736 generic phase: 5
    2017/11/13 07:41:37 [debug] 624#0: *244736 generic phase: 6
    2017/11/13 07:41:37 [debug] 624#0: *244736 generic phase: 7
    2017/11/13 07:41:37 [debug] 624#0: *244736 generic phase: 8

    2017/11/13 07:41:37 [debug] 624#0: *244736 http script var: "Q^Y,m"
    2017/11/13 07:41:37 [debug] 624#0: *244736 limit conn: 4B30596F 1
    2017/11/13 07:41:37 [debug] 624#0: *244736 access phase: 9
    2017/11/13 07:41:37 [debug] 624#0: *244736 access phase: 10
    2017/11/13 07:41:37 [debug] 624#0: *244736 post access phase: 11

2. 2017/11/13 07:41:37 [debug] 624#0: *244736 http script copy: "Connection: close^M"
    2017/11/13 07:41:37 [debug] 624#0: *244736 http script copy: ""
    2017/11/13 07:41:37 [debug] 624#0: *244736 http script copy: ""
    2017/11/13 07:41:37 [debug] 624#0: *244736 http script copy: ""
    2017/11/13 07:41:37 [debug] 624#0: *244736 http script copy: ""
Последние 4 пустых строки

3. 2017/11/13 07:41:37 [debug] 624#0: *244736 http cleanup add: 0000000001F02220
    2017/11/13 07:41:37 [debug] 624#0: *244736 get rr peer, try: 1
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream connect: -2
    2017/11/13 07:41:37 [debug] 624#0: *244736 http finalize request: -4, "/?" a:1, c:2
    2017/11/13 07:41:37 [debug] 624#0: *244736 http request count:2 blk:0
    2017/11/13 07:41:37 [debug] 624#0: *244736 http run request: "/?"
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream check client, write event:1, "/"
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream recv(): -1 (11: Resource temporarily unavailable)

Здесь особо интересует (11: Resource temporarily unavailable). Запрос делался в корень методом HEAD
Потому что дальше, вроде бы, все в порядке:
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream request: "/?"
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream send request handler
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream send request
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream send request body
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream request: "/?"
    2017/11/13 07:41:37 [debug] 624#0: *244736 http upstream process header
    2017/11/13 07:41:37 [debug] 624#0: *244736 http proxy status 200 "200 OK"

4. 2017/11/13 07:41:37 [debug] 624#0: *244736 http write filter: l:1 f:0 s:298
    2017/11/13 07:41:37 [debug] 624#0: *244736 http write filter limit 0
    2017/11/13 07:41:37 [debug] 624#0: *244736 http write filter 0000000000000000
    2017/11/13 07:41:37 [debug] 624#0: *244736 finalize http upstream request: 0
    2017/11/13 07:41:37 [debug] 624#0: *244736 finalize http proxy request
    2017/11/13 07:41:37 [debug] 624#0: *244736 free rr peer 1 0
    2017/11/13 07:41:37 [debug] 624#0: *244736 close http upstream connection: 5
    2017/11/13 07:41:37 [debug] 624#0: *244736 http finalize request: 0, "/?" a:1, c:1
    2017/11/13 07:41:37 [debug] 624#0: *244736 set http keepalive handler
    2017/11/13 07:41:37 [debug] 624#0: *244736 http close request

Спасибо.
--
----------- следущая часть -----------
Вложение в формате HTML было извлечено…
URL: <http://mailman.nginx.org/pipermail/nginx-ru/attachments/20171113/80b67f4c/attachment.html>