perf(*) make some heavily used code paths more cooperative by yielding (

#8888)

### Summary

Adds yielding to some hot paths that otherwise may cause latency spikes
with huge Kong configurations. The special focus was to make CP/DP config
changes less blocking.

kong/api/routes/config.lua

@@ -5,7 +5,7 @@ local errors = require("kong.db.errors")
 
 local kong = kong
 local ngx = ngx
-local dc = declarative.new_config(kong.configuration)
+local type = type
 local table = table
 local tostring = tostring
 
@@ -71,6 +71,8 @@ return {
       end
       self.params.check_hash = nil
 
+      local dc = declarative.new_config(kong.configuration)
+
       local entities, _, err_t, meta, new_hash
       if self.params._format_version then
         entities, _, err_t, meta, new_hash = dc:parse_table(self.params)

kong/clustering/control_plane.lua

@@ -13,6 +13,7 @@ local setmetatable = setmetatable
 local type = type
 local pcall = pcall
 local pairs = pairs
+local yield = utils.yield
 local ipairs = ipairs
 local tonumber = tonumber
 local ngx = ngx
@@ -235,11 +236,20 @@ function _M:export_deflated_reconfigure_payload()
 
   self.reconfigure_payload = payload
 
-  payload, err = deflate_gzip(cjson_encode(payload))
+  payload, err = cjson_encode(payload)
   if not payload then
     return nil, err
   end
 
+  yield()
+
+  payload, err = deflate_gzip(payload)
+  if not payload then
+    return nil, err
+  end
+
+  yield()
+
   self.current_hashes = hashes
   self.current_config_hash = config_hash
   self.deflated_reconfigure_payload = payload

kong/clustering/data_plane.lua

@@ -6,6 +6,9 @@ local ws_client = require("resty.websocket.client")
 local cjson = require("cjson.safe")
 local declarative = require("kong.db.declarative")
 local constants = require("kong.constants")
+local utils = require("kong.tools.utils")
+
+
 local assert = assert
 local setmetatable = setmetatable
 local math = math
@@ -20,8 +23,8 @@ local cjson_encode = cjson.encode
 local kong = kong
 local exiting = ngx.worker.exiting
 local ngx_time = ngx.time
-
-local inflate_gzip = require("kong.tools.utils").inflate_gzip
+local inflate_gzip = utils.inflate_gzip
+local yield = utils.yield
 
 
 local KONG_VERSION = kong.version
@@ -247,8 +250,10 @@ function _M:communicate(premature)
 
         if typ == "binary" then
           data = assert(inflate_gzip(data))
+          yield()
 
           local msg = assert(cjson_decode(data))
+          yield()
 
           if msg.type == "reconfigure" then
             if msg.timestamp then

kong/clustering/init.lua

@@ -21,12 +21,15 @@ local assert = assert
 local error = error
 local concat = table.concat
 local pairs = pairs
+local yield = require("kong.tools.utils").yield
 local sort = table.sort
 local type = type
 
+
 local ngx_ERR = ngx.ERR
 local ngx_DEBUG = ngx.DEBUG
 
+
 local DECLARATIVE_EMPTY_CONFIG_HASH = constants.DECLARATIVE_EMPTY_CONFIG_HASH
 local _log_prefix = "[clustering] "
 
@@ -35,6 +38,8 @@ local MT = { __index = _M, }
 
 
 local function to_sorted_string(value)
+  yield(true)
+
   if value == ngx_null then
     return "/null/"
   end

kong/db/declarative/init.lua

@@ -909,7 +909,7 @@ function declarative.load_into_cache(entities, meta, hash)
   end
 
   for tag_name, tags in pairs(tags_by_name) do
-    yield()
+    yield(true)
 
     -- tags:admin|@list -> all tags tagged "admin", regardless of the entity type
     -- each tag is encoded as a string with the format "admin|services|uuid", where uuid is the service uuid
@@ -942,6 +942,8 @@ function declarative.load_into_cache(entities, meta, hash)
   kong.core_cache:purge()
   kong.cache:purge()
 
+  yield()
+
   return true, nil, default_workspace
 end
 

kong/db/schema/init.lua

@@ -16,6 +16,7 @@ local insert       = table.insert
 local format       = string.format
 local unpack       = unpack
 local assert       = assert
+local yield        = utils.yield
 local pairs        = pairs
 local pcall        = pcall
 local floor        = math.floor
@@ -846,6 +847,8 @@ local validate_fields
 -- @return true if the field validates correctly;
 -- nil and an error message on failure.
 function Schema:validate_field(field, value)
+  yield(true)
+
   if value == null then
     if field.ne == null then
       return nil, field.err or validation_errors.NE:format("null")
@@ -1601,6 +1604,8 @@ end
 -- appropriate updated values (except for "select" context
 -- it does it in place by modifying the data directly).
 function Schema:process_auto_fields(data, context, nulls, opts)
+  yield(true)
+
   local check_immutable_fields = false
 
   local is_select = context == "select"

kong/db/schema/others/declarative_config.lua

@@ -12,12 +12,13 @@ local null = ngx.null
 local type = type
 local next = next
 local pairs = pairs
+local yield = utils.yield
 local ipairs = ipairs
 local insert = table.insert
 local concat = table.concat
 local tostring = tostring
 local cjson_encode = require("cjson.safe").encode
-local yield = require("kong.tools.utils").yield
+
 
 local DeclarativeConfig = {}
 
@@ -276,6 +277,8 @@ end
 
 local function populate_references(input, known_entities, by_id, by_key, expected, parent_entity)
   for _, entity in ipairs(known_entities) do
+    yield(true)
+
     if type(input[entity]) ~= "table" then
       goto continue
     end
@@ -295,6 +298,7 @@ local function populate_references(input, known_entities, by_id, by_key, expecte
 
     local entity_schema = all_schemas[entity]
     for i, item in ipairs(input[entity]) do
+      yield(true)
 
       populate_references(item, known_entities, by_id, by_key, expected, entity)
 
@@ -352,6 +356,8 @@ local function validate_references(self, input)
   local errors = {}
 
   for a, as in pairs(expected) do
+    yield(true)
+
     for b, bs in pairs(as) do
       for _, k in ipairs(bs) do
         local key = k.value

kong/db/strategies/off/init.lua

@@ -167,8 +167,6 @@ local function page_for_key(self, key, size, offset, options)
       break
     end
 
-    yield(true)
-
     -- Tags are stored in the cache entries "tags||@list" and "tags:<tagname>|@list"
     -- The contents of both of these entries is an array of strings
     -- Each of these strings has the form "<tag>|<entity_name>|<entity_id>"

kong/tools/utils.lua

@@ -1418,20 +1418,24 @@ _M.topological_sort = topological_sort
 
 
 do
-  local counter = 0
-  function _M.yield(in_loop, phase)
-    phase = phase or get_phase()
-    if phase == "init" or phase == "init_worker"  then
-      return
-    end
-    if in_loop then
-      counter = counter + 1
-      if counter % YIELD_ITERATIONS ~= 0 then
+  if ngx.IS_CLI then
+    function _M.yield() end
+  else
+    local counter = 0
+    function _M.yield(in_loop, phase)
+      phase = phase or get_phase()
+      if phase == "init" or phase == "init_worker" then
         return
       end
-      counter = 0
+      if in_loop then
+        counter = counter + 1
+        if counter % YIELD_ITERATIONS ~= 0 then
+          return
+        end
+        counter = 0
+      end
+      ngx_sleep(0)
     end
-    ngx_sleep(0)
   end
 end