bug: Strings in luajit are infinitely bloated, even if they are not rereferenced in the lua vm

[fairyqb]

Current Behavior

Minimal example code

resty example.lua

`
local function get_memory_usage()
local b = collectgarbage("count") * 1024
return b
end

local my_table = {}  
for i = 1, 10000000 do  
    my_table[i] =  string.rep("A" , 256) .. i  

end

my_table = nil
print("start gc:", "mem:",get_memory_usage())
collectgarbage("collect") 
print("end gc:", "mem:",get_memory_usage())
print("sleep 10m")

print("done")
ngx.sleep(60*10*6)

`

Strings in luajit are infinitely bloated, even if they are not rereferenced in the lua vm. As a result, the memory resources of the nginx process RES are increasing to become larger and larger.

Expected Behavior

why?

Error Logs

none

Steps to Reproduce

none

Environment

• APISIX version (run apisix version):
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):
  aspsix all version

[Revolyssup]

@fairyqb This is not an apisix related bug but rather limitations/issues related with luajit itself. I dont think this can be fixed at the APISIX end. // @shreemaan-abhishek

[fairyqb]

@fairyqb This is not an apisix related bug but rather limitations/issues related with luajit itself. I dont think this can be fixed at the APISIX end. // @shreemaan-abhishek

Is this a bug in openresty/apisix, or a bug in luajit, and this issue is not solved? Worrying about applying APISIX to production?

[Revolyssup]

I think you can ask this query here https://github.com/openresty/openresty

[membphis]

you can research the Luajit gc, here is another example which can show more information than yours:

result:

case 1:
Memory usage after garbage collection: 4319.6220703125 KB
Memory usage after garbage collection: 1247.5986328125 KB
Memory usage after garbage collection: 479.5361328125 KB
Memory usage after garbage collection: 287.5361328125 KB

source code:

ngx.say("\ncase 1:")
local my_table = {}
for i = 1, 1000 * 1000 do  
    my_table[i] =  string.rep("A" , 256) .. i
end
my_table = nil

for i = 1, 100, 1 do
    collectgarbage("collect")

    local memory_usage = collectgarbage("count")
    print("Memory usage after garbage collection: " .. memory_usage .. " KB")

    if memory_usage < 300 then
        break
    end

    ngx.sleep(1)
end