openresty lua buffer is writing only 4kb file from buffer

Hi ,

This is our openresty lua code

ngx.say("success")
ngx.eof()
local function write_to_file()
local args = ngx.req.get_uri_args()
local file, err = io.open("/home/ubuntu/lua_files/lua_dir/example.csv", "a")
if file==nil then
ngx.say("Couldn't open file: "..err)
else
file:setvbuf("full", 1000000)
for key, val in pairs(args) do
file:write(val," ")
end
file:close()
end
end
ngx.thread.spawn(write_to_file)

When we use above code to lua to maintain buuffer of 1mb in, but it is writing 4kb to file on periodically based on inoming requests

The issue provides only an inline OpenResty Lua snippet centered on write_to_file and file:setvbuf; no repository file or test is named. Start by reproducing the request-driven writes and inspect the module's documented buffering behavior; done means identifying whether 4 KB writes are expected and specifying a verified fix or explanation.