perf: make inserting host match route several times faster (#62)

Previously, `insert_route` will sort the table with `table.sort`.
The `table.sort` is implemented via quick-sort, which is in O(nlogn)
complexity and perform worse when the table is already mostly sorted.

Since we can ensure the table is sorted before inserting, we can
implement a naive insert sort in O(n) complexity to replace `table.sort`.

Via `time resty -I=./lib -I=./deps/share/lua/5.1 benchmark/match-hosts.lua`
I see an impressive time reduction with this optimization.

benchmark/match-hosts.lua

@@ -5,7 +5,7 @@ local match_times = 1000 * 100
 local path = "/12345"
 local routes = {}
 for i = 1, route_count do
-    routes[i] = {paths = {path}, hosts = {ngx.md5(i)}, metadata = i}
+    routes[i] = {paths = {path}, priority = i, hosts = {ngx.md5(i)}, metadata = i}
 end
 
 local rx = radix.new(routes)

benchmark/match-wildcard-hosts.lua

@@ -5,7 +5,7 @@ local match_times = 1000 * 50
 local path = "/12345"
 local routes = {}
 for i = 1, route_count do
-    routes[i] = {paths = {path}, hosts = {"*." .. ngx.md5(i)}, metadata = i}
+    routes[i] = {paths = {path}, priority = i, hosts = {"*." .. ngx.md5(i)}, metadata = i}
 end
 
 local rx = radix.new(routes)

lib/resty/radixtree.lua

@@ -27,6 +27,7 @@ local ngx         = ngx
 local table       = table
 local clear_tab   = base.clear_tab
 local new_tab     = base.new_tab
+local move_tab    = table.move
 local tonumber    = tonumber
 local ipairs      = ipairs
 local ffi         = require("ffi")
@@ -49,7 +50,6 @@ local cur_level   = ngx.config.subsystem == "http" and
 local ngx_var     = ngx.var
 local re_find     = ngx.re.find
 local re_match    = ngx.re.match
-local sort_tab    = table.sort
 local ngx_re      = require("ngx.re")
 local ngx_null    = ngx.null
 local empty_table = {}
@@ -179,6 +179,16 @@ local function sort_route(route_a, route_b)
     return (route_a.priority or 0) > (route_b.priority or 0)
 end
 
+local function insert_tab_in_order(tab, val, func)
+    for i, elem in ipairs(tab) do
+        if func(val, elem) then
+            move_tab(tab, i, #tab, i + 1)
+            tab[i] = val
+            return
+        end
+    end
+    insert_tab(tab, val)
+end
 
 local function insert_route(self, opts)
     local path = opts.path
@@ -190,10 +200,9 @@ local function insert_route(self, opts)
         if not self.hash_path[path] then
             self.hash_path[path] = {opts}
         else
-            insert_tab(self.hash_path[path], opts)
+            insert_tab_in_order(self.hash_path[path], opts, sort_route)
         end
 
-        sort_tab(self.hash_path[path], sort_route)
         return true
     end
 
@@ -202,8 +211,7 @@ local function insert_route(self, opts)
         local idx = tonumber(ffi_cast('intptr_t', data_idx))
         local routes = self.match_data[idx]
         if routes and routes[1].path == path then
-            insert_tab(routes, opts)
-            sort_tab(routes, sort_route)
+            insert_tab_in_order(routes, opts, sort_route)
             return true
         end
     end