request: Expect monitoring metrics to add monitoring of nginx shared memory usage

[chanjet1213]

Issue description

期待监控指标添加对nginx共享内存使用情况的监控

Environment

• apisix version (cmd: apisix version):
• OS (cmd: uname -a):
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API):
• apisix-dashboard version, if have:
• the plugin runner version, if the issue is about a plugin runner (cmd: depended on the kind of runner):
• luarocks version, if the issue is about installation (cmd: luarocks --version):

[tzssangglass]

It seems to be quite difficult, and if you use the ngx.shared.DICT API to monitor it, it will lose performance.

refer to: https://github.com/openresty/lua-nginx-module#ngxshareddictcapacity

[kwanhur]

Is it like ngx_slab_stats? Which supports shared memory allocated from lua-nginx-module.

[tzssangglass]

I changed my mind and I think it's a meaningful enhancemen.

Perhaps we can first monitor the nginx.shared.DICT that is used by APISIX, and next we allow users to monitor a custom nginx.shared.DICT (or read the used nginx.shared.DICT directly from the configuration file).

cc @spacewander

[tokers]

I changed my mind and I think it's a meaningful enhancemen.

Perhaps we can first monitor the nginx.shared.DICT that is used by APISIX, and next we allow users to monitor a custom nginx.shared.DICT (or read the used nginx.shared.DICT directly from the configuration file).

cc @spacewander

@tzssangglass Could you share your proposal?

[tzssangglass]

@tzssangglass Could you share your proposal?

we can use ngx.shared.DICT.capacity and ngx.shared.DICT.free_space to monitor a ngx.shared.DICT?

[tokers]

@tzssangglass Could you share your proposal?

we can use ngx.shared.DICT.capacity and ngx.shared.DICT.free_space to monitor a ngx.shared.DICT?

OK so we may get a curve about the shared dict, in the diagram we can see the shared dict memory usage.

[ccxhwmy]

@tzssangglass Could you share your proposal?

we can use ngx.shared.DICT.capacity and ngx.shared.DICT.free_space to monitor a ngx.shared.DICT?

I found that nginx adopts a way of pre-allocating memory for shared DICT, the smallest granularity is page, ranther than allocat per use. The value of ngx.shared.DICT.capacity is accurate, but ngx.shared.DICT.free_space is the value left after the acquired pre-allocated memory, so there is a certain inconsistency in fine-grained ngx.shared.DICT.free_space accurate.

[tzssangglass]

I found that nginx adopts a way of pre-allocating memory for shared DICT, the smallest granularity is page, ranther than allocat per use. The value of ngx.shared.DICT.capacity is accurate, but ngx.shared.DICT.free_space is the value left after the acquired pre-allocated memory, so there is a certain inconsistency in fine-grained ngx.shared.DICT.free_space accurate.

Is there some docs or code that explain this? This is useful info.

[ccxhwmy]

I found that nginx adopts a way of pre-allocating memory for shared DICT, the smallest granularity is page, ranther than allocat per use. The value of ngx.shared.DICT.capacity is accurate, but ngx.shared.DICT.free_space is the value left after the acquired pre-allocated memory, so there is a certain inconsistency in fine-grained ngx.shared.DICT.free_space accurate.

Is there some docs or code that explain this? This is useful info.

I checked the C code of ngx.shared.DICT, the ffi call function of free_space is ngx_http_lua_ffi_shdict_free_space, and the caluculation method is bytes = ctx->shpool->pfree * ngx_pagesize;. The ffi calling process of set is ngx_http_lua_ffi_shdict_store->ngx_slab_alloc_locked->ngx_slab_alloc_pages, it will judge whether the memory previously malloc is enough, if it is enough, it will not malloc memory. pfree will only be modified when entering ngx_slab_alloc_pages to malloc memory.

[tzssangglass]

Hi @ccxhwmy , would you like to work on this?

[ccxhwmy]

Hi @ccxhwmy , would you like to work on this?

Can you tell me which plugin I can modify to get information of ngx.shared.DICT regularly and report it? prometheus?

[tzssangglass]

Can you tell me which plugin I can modify to get information of ngx.shared.DICT regularly and report it? prometheus?

yes, prometheus.