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ngx_debug_pool.md

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ngx_debug_pool

This module provides access to information of memory usage for nginx/tengine memory pool.

Example

get information of worker process

 http {
    server {
        listen 80;

        location = /debug_pool {
            debug_pool;
        }
    }
 }

Requesting URI /debug_pool, you will get information of memory usage for worker process which gets this request.
The output page may look like as follows:

$ curl http://localhost:80/debug_pool
pid:18821
size:      223784 num:           2 cnum:           1 lnum:          10 ngx_init_cycle
size:        1536 num:           4 cnum:           1 lnum:          10 ngx_event_accept
size:           0 num:           1 cnum:           0 lnum:           0 ngx_http_lua_create_fake_request
size:           0 num:           1 cnum:           0 lnum:           0 main
size:           0 num:           1 cnum:           0 lnum:           0 ngx_http_lua_create_fake_connection
size:           0 num:           1 cnum:           0 lnum:           6 ngx_http_server_names
size:        8192 num:           4 cnum:           1 lnum:           0 ngx_http_create_request
size:           0 num:           1 cnum:           0 lnum:           0 ngx_http_lua_init_worker
size:       228KB num:          15 cnum:           3 lnum:          26 [SUMMARY]

get information of specific process

Also you can use gdb script debug_pool.gdb to get information of specific process.
Some process cannot handle HTTP request, such as master process or tengine Proc process.
The following example shows how to get information of master process.

$ gdb -q -x debug_pool.gdb -p <pid of master process>
(gdb) debug_pool
size:       16384 num:           1 cnum:           1 lnum:           0 ngx_http_user_agent_create_main_conf:24
size:           0 num:           1 cnum:           0 lnum:           0 main:224
size:      150312 num:           2 cnum:           1 lnum:          13 ngx_init_cycle:824
size:      166696 num:           4 cnum:           2 lnum:          13 [SUMMARY]

Data

Every line except the last one of output content has the same format, as follows:

"size: %12u num: %12u cnum: %12u lnum: %12u <function name>"

  • size: size of current used memory of this pool
  • num: number of created pool (including current used pool and destroyed pool)
  • cnum: number of current used pool
  • lnum: number of calling ngx_palloc_large()
  • funcion name: which nginx/tengine C function creates this pool
    • With function name of pool creator, we can know memory usage of every module, for example:
    • pool created by ngx_http_create_request is used for one HTTP request.
      • Because most modules allocates memory from this pool directly, it's hard to distinguish between them.
    • pool created by ngx_event_accept is used for one TCP connection.
    • pool created by ngx_init_cycle is used for parsing nginx/tengine configuration and keeping other global data structures.
    • pool created by ngx_http_lua_init_worker is used for conf.temp_pool of directive init_worker_by_lua.
    • ...

Last line of output content summarizes the information of all memory pools.

Install

$ ./configure --add-module=./modules/ngx_debug_pool
$ make && make install

Directive

Syntax: debug_pool

Default: none

Context: server, location

The information of nginx/tengine memory pool usage will be accessible from the surrounding location.

Exception

Memory allocated without using memory pool does not get taken into account with this module.
For example, ngx_http_spdy_module allocates a temporary buffer via malloc(ngx_alloc) for raw data of SYN_REPLY frame. After being compressed, this buffer will be freed immediately.