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used table functions of LuaJIT for better performance. #3673

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Feb 1, 2019
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used table functions of LuaJIT for better performance. #3673

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15 changes: 10 additions & 5 deletions rootfs/etc/nginx/lua/monitor.lua
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Original file line number Diff line number Diff line change
@@ -1,12 +1,16 @@
local socket = ngx.socket.tcp
local cjson = require("cjson.safe")
local assert = assert
local new_tab = require "table.new"
local clear_tab = require "table.clear"
local clone_tab = require "table.clone"

local metrics_batch = {}
-- if an Nginx worker processes more than (MAX_BATCH_SIZE/FLUSH_INTERVAL) RPS then it will start dropping metrics
local MAX_BATCH_SIZE = 10000
local FLUSH_INTERVAL = 1 -- second

local metrics_batch = new_tab(MAX_BATCH_SIZE, 0)
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What's the second argument for? Why 0? A link to docs would be sufficient too.

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doc: https://github.com/openresty/luajit2/blob/v2.1-agentzh/doc/extensions.html
table.new(narray, nhash), the second argument is for hash.


local _M = {}

local function send(payload)
Expand Down Expand Up @@ -46,8 +50,8 @@ local function flush(premature)
return
end

local current_metrics_batch = metrics_batch
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You are changing the behaviour here. The idea was to take current batch as soon as timer calls flush function and reset the main queue so that it can accept more metrics and continue with encoding and sending the current metrics batch while the other one is being filled.

With your change we will potentially lose more metrics. Imagine timer (flush function) kicks in right before the time when the current batch is full. It'll start encoding the metrics and during this time every new metric will be dropped. Given cjson is quite fast at encoding there'll probably not many metrics being dropped but if we can avoid that why not.

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got it. I will fix that.

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@ElvinEfendi fixed.
used table.clone to clone table: https://github.com/openresty/luajit2/blob/v2.1-agentzh/README#L65

metrics_batch = {}
local current_metrics_batch = clone_tab(metrics_batch)
clear_tab(metrics_batch)

local payload, err = cjson.encode(current_metrics_batch)
if not payload then
Expand All @@ -66,12 +70,13 @@ function _M.init_worker()
end

function _M.call()
if #metrics_batch >= MAX_BATCH_SIZE then
local metrics_size = #metrics_batch
if metrics_size >= MAX_BATCH_SIZE then
ngx.log(ngx.WARN, "omitting metrics for the request, current batch is full")
return
end

table.insert(metrics_batch, metrics())
metrics_batch[metrics_size + 1] = metrics()
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Does this custom table implementation not have insert?

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it has the insert method, but the table.insert is an O(n) operation due to the lj_tab_len call inside LuaJIT.
We can avoid it in hot loops for better performance.

end

if _TEST then
Expand Down