diff --git a/cnt.lua b/cnt.lua
index ea8e01b..65c460d 100644
--- a/cnt.lua
+++ b/cnt.lua
@@ -20,7 +20,8 @@ function box.counter.inc(space, ...)
         tuple = box.update(space, key, '+p', cnt_index, 1)
         if tuple ~= nil then break end
         local data = {...}
-        table.insert(data, 1)
+	data[#data + 1] = 1
+--        table.insert(data, 1) 
         tuple = box.insert(space, unpack(data))
         if tuple ~= nil then break end
     end
diff --git a/expirationd.lua b/expirationd.lua
index 6d488ae..1809cdd 100644
--- a/expirationd.lua
+++ b/expirationd.lua
@@ -14,16 +14,18 @@
 
 -- Create a new table with constant members. A runtime error
 -- is raised on attempt to change a table field.
+
+local concat = table.concat
+
 local function finalize_table(table)
     return setmetatable ({}, {
                              __index = table,
                              __newindex = function(table_arg,
                                                    name_arg,
                                                    value_arg)
-                                 error("attempt to change constant " ..
-                                       tostring(name_arg) ..
-                                       " to "
-                                       .. tostring(value_arg), 2)
+                                 error(concat{"attempt to change constant ",
+                                       tostring(name_arg), " to ",
+				       tostring(value_arg), 2})
                              end
                              })
 end
@@ -83,8 +85,7 @@ local function worker_loop(task)
             if checks >= task.tuples_per_iter then
                 checks = 0
                 if scan_space:len() > 0 then
-                    local delay = (task.tuples_per_iter * task.full_scan_time)
-                        / scan_space:len()
+                    local delay = (task.tuples_per_iter * task.full_scan_time) * (1 / scan_space:len())
 
                     if delay > expirationd.constants.max_delay then
                         delay = expirationd.constants.max_delay
@@ -107,16 +108,16 @@ end
 local function guardian_loop(task)
     -- detach the guardian from the creator and attach it to sched
     box.fiber.detach()
-    box.fiber.name("guardian of "..task.name)
+    box.fiber.name(concat{"guardian of ", task.name})
 
-    print("expiration: task '" .. task.name .. "' started")
+    print(concat{"expiration: task '", task.name, "' started"})
     -- create a worker fiber
     task.worker_fiber = box.fiber.create(worker_loop)
     box.fiber.resume(task.worker_fiber, task)
 
     while true do
         if task.worker_fiber:id() == 0 then
-            print("expiration: task '" .. task.name .. "' restarted")
+            print(concat{"expiration: task '", task.name, "' restarted"})
             task.restarts = task.restarts + 1
             -- create worker fiber
             task.worker_fiber = box.fiber.create(worker_loop)
@@ -160,7 +161,7 @@ local function get_task(name)
 
     -- check, does the task exist
     if task_list[name] == nil then
-        error("task '" .. name .. "' doesn't exist")
+        error(concat{"task '", name, "' doesn't exist"})
     end
 
     return task_list[name]
@@ -243,7 +244,7 @@ function expirationd.run_task(name,
 
     -- check, does the task exist
     if task_list[name] ~= nil then
-        error("task '" .. name .. "' already running")
+        error(concat{"task '", name, "' already running"})
     end
     local task = create_task(name)
 
@@ -320,17 +321,17 @@ end
 --
 function expirationd.show_task_list(print_head)
     if print_head == nil or print_head == true then
-        print("name" .. "\t" ..
-              "space" .. "\t" ..
-              "expired" .. "\t" ..
-              "time")
+        print(concat{"name", "\t",
+              "space", "\t",
+              "expired", "\t",
+              "time"})
         print("-----------------------------------")
     end
     for i, task in pairs(task_list) do
-        print(task.name .. "\t" ..
-              task.space_no .. "\t" ..
-              task.tuples_expired .. "\t" ..
-              math.floor(os.time() - task.start_time))
+        print(concat{task.name, "\t", 
+              task.space_no, "\t",
+              task.tuples_expired, "\t",
+              math.floor(os.time() - task.start_time)})
     end
 end
 
@@ -399,7 +400,7 @@ end
 
 -- generate email string
 local function get_email(uid)
-    local email = "test_" .. uid .. "@sex.com"
+    local email = concat{"test_", uid, "@sex.com"}
     return email
 end
 
diff --git a/notifications.lua b/notifications.lua
index 8d8f690..9ed424b 100644
--- a/notifications.lua
+++ b/notifications.lua
@@ -63,7 +63,7 @@ local ring_max = 20
 -- field index of the first ring in the tuple.
 -- field 0 - user id, field 1 - total unread count, hence
 local ring0_fieldno = 2
-
+local concat = table.concat
 -- Find the tuple associated with user id or create a new
 -- one.
 function notification_find_or_insert(user_id)
@@ -74,8 +74,10 @@ function notification_find_or_insert(user_id)
     -- create an empty ring for each notification type
     local rings = {}
     for i = 1, #notification_types do
-        table.insert(rings, 0) -- unread count - 0
-        table.insert(rings, "") -- notification list - empty
+	  rings[#rings + 1] = 0
+	  rings[#rings + 1] = ""
+--        table.insert(rings, 0) -- unread count - 0
+--        table.insert(rings, "") -- notification list - empty
     end
     box.insert(space_no, user_id, 0, unpack(rings))
     -- we can't use the tuple returned by box.insert, since it could
@@ -99,15 +101,17 @@ end
 -- false len(ring) when not found
 --
 local function is_duplicate(ring, id, tail_offset)
-    id_len = #id
-    id = string.sub(id, 1, id_len - tail_offset)
+    local id_len = #id
+    local id_len_min = id_len - 1
+    local sub = string.sub
+    local id = sub(id, 1, id_len - tail_offset)
     for i=1, #ring, id_len do
-        n_id = string.sub(ring, i, i+id_len-1 - tail_offset)
+        n_id = sub(ring, i, i+ id_len_min - tail_offset)
         if  n_id == id then
             -- we're going to insert a new notifiation,
             -- return the old notification offset relative to
             -- the new field size
-            return true, i - 1 + id_len
+            return true, i + id_len_min
         end
     end
     return false, ring_max * id_len
@@ -138,10 +142,13 @@ function notification_push(user_id, ring_no, id)
     -- check if the counters need to be updated
     if unread_count < ring_max and dup_offset > unread_count * #id then
     -- prepend ++total_unread_count, ++unread_count to our update operation
-        format = "+p+p"..format
+        format = concat{"+p+p", format}
         local args1 = args
         args = { 1, 1, fieldno, 1 }
-        for _, v in ipairs(args1) do table.insert(args, v) end
+        for _, v in ipairs(args1) do
+	--	table.insert(args, v)
+		args[#args + 1 ] = v
+	end
     end
     return box.update(space_no, user_id, format, unpack(args))
 end
@@ -158,15 +165,18 @@ function notification_read(user_id, ring_no)
     local return_fields = {}
     local k, v = tuple:next()
     local k, v = tuple:next(k) -- skip user id
-    table.insert(return_fields, v) -- total unread count
+    return_fields[#return_fields + 1] = v
+--    table.insert(return_fields, v) -- total unread count
     k, v = tuple:next(k) -- now at the first ring
     while k ~= nil do
-        table.insert(return_fields, v) -- insert unread count
+    	return_fields[#return_fields + 1] = v
+--        table.insert(return_fields, v) -- insert unread count
         k, v = tuple:next(k)
         if k ~= nil then
             k, v = tuple:next(k) -- skip this ring data
         end
     end
-    table.insert(return_fields, tuple[fieldno+1]) -- insert ring data
+    return_fields[#return_fields + 1] = tuple[fieldno+1]
+--    table.insert(return_fields, tuple[fieldno+1]) -- insert ring data
     return return_fields
 end
diff --git a/profiles.lua b/profiles.lua
index c304f86..31c1ff1 100644
--- a/profiles.lua
+++ b/profiles.lua
@@ -82,9 +82,11 @@ local function store_profile(profile)
     -- put preference to tuple
     for pref_id, pref_value in pairs(profile.prefs) do
 	-- insert preference id
-	table.insert(tuple, pref_id)
+--	table.insert(tuple, pref_id)
+	tuple[#tuple + 1] = pref_id
 	-- insert preference value
-	table.insert(tuple, pref_value)
+	tuple[#tuple + 1] = pref_value
+--	table.insert(tuple, pref_value)
     end
     return box.replace(space_no, unpack(tuple))
 end
diff --git a/sorted_array.lua b/sorted_array.lua
index 3797dfe..732ab40 100644
--- a/sorted_array.lua
+++ b/sorted_array.lua
@@ -6,7 +6,7 @@ local floor = require("math").floor
 local function s_to_a(data)
     local a = {}
     local bytes = {string.byte(data, i, #data)}
-    for i = 1, #data / 8 do
+    for i = 1, #data * 0.125 do -- #data * 0.125 will faster then #data/8
 	a[i] = 0
 	for c = 0, 7 do
 	    a[i] = bit.lshift(a[i], 8)
@@ -20,7 +20,8 @@ local function a_to_s(a)
     local bytes = {}
     for i = 1, #a do
 	for c = 0, 7 do
-	    table.insert(bytes, bit.band(a[i], 0xff))
+	    bytes[#bytes + 1] =  bit.band(a[i], 0xff)
+	    --table.insert(bytes, bit.band(a[i], 0xff))
 	    a[i] = bit.rshift(a[i], 8)
 	end
     end
@@ -33,18 +34,22 @@ local function amerge(a, b)
     local n = limit
     while #a > 0 and #b > 0 and n > 0 do
 	if a[1] > b[1] then
-	    table.insert(r, table.remove(a, 1))
+	    r[#r + 1] = table.remove(a, 1)
+	    --table.insert(r, table.remove(a, 1))
 	else
-	    table.insert(r, table.remove(b, 1))
+	    r[#r + 1] = table.remove(b, 1)
+	    --table.insert(r, table.remove(b, 1))
 	end
 	n = n - 1
     end
     while #a > 0 and n > 0 do
-	table.insert(r, table.remove(a, 1))
+	r[#r + 1] = table.remove(a, 1)
+	--table.insert(r, table.remove(a, 1))
                 n = n - 1
     end
     while #b > 0 and n > 0 do
-	table.insert(r, table.remove(b, 1))
+	r[#r + 1] = table.remove(b, 1)
+	--table.insert(r, table.remove(b, 1))
 	n = n - 1
     end
     return r
@@ -58,7 +63,7 @@ local function afind_ge(a, x)
     local first, last  = 1, #a
     local mid
     repeat
-	mid = floor(first + (last - first) / 2)
+	mid = floor(first + (last - first) * 0.5)
 	if x > a[mid] then
 	    last = mid
 	else
@@ -89,7 +94,7 @@ local function ains(a, key)
 end
 
 local function adel(a, key)
-    key = tonumber(key)
+    local key = tonumber(key)
     local i = afind_ge(a, key)
     if a[i] == key then
 	table.remove(a, i)
@@ -145,7 +150,8 @@ function box.sa_select(space, key, from, limit)
 	if a[i] == nil then
 	    break
 	end
-	table.insert(r, a[i])
+	r[#r + 1] = a[i]
+	--table.insert(r, a[i])
 	limit = limit - 1
 	if limit == 0 then
 	    break
diff --git a/statistics.lua b/statistics.lua
index 3fe99a3..db9875b 100644
--- a/statistics.lua
+++ b/statistics.lua
@@ -1,6 +1,8 @@
-field_count = 10
-timeout = 0.006
-max_attempts = 5
+local field_count = 10
+local timeout = 0.006
+local max_attempts = 5
+local concat = table.concat
+local sub = string.sub
 
 function increment_or_insert(space, key, field)
     retry = true
@@ -14,7 +16,7 @@ function increment_or_insert(space, key, field)
 	    --insert new tuple
 		tuple = {}
 		for i = 2, field_count do tuple[i] = 0 end
-		tuple[1] = string.sub(key, -8)
+		tuple[1] = sub(key, -8)
 		tuple[tonumber(field)] = 1
 		box.insert(space, key, unpack(tuple))
 	    end
@@ -22,7 +24,7 @@ function increment_or_insert(space, key, field)
 	--exception
 	    count = count + 1
 	    if count == max_attempts then
-		print("max attempts reached for space="..space.." key="..key.." field="..field)
+		print(concat{"max attempts reached for space=",space," key=",key," field=",field})
 		break
 	    end
 	    box.fiber.sleep(timeout)
@@ -42,7 +44,7 @@ function increment_or_insert_2(space, key, field, element1, element2)
         --insert new tuple
         tuple = {}
         for i = 2, field_count + 2 do tuple[i] = 0 end
-        tuple[1] = string.sub(key, -8)
+        tuple[1] = sub(key, -8)
         tuple[tonumber(field)] = 1
         tuple[field_count + 1] = element1
         tuple[field_count + 2] = element2
@@ -52,7 +54,7 @@ function increment_or_insert_2(space, key, field, element1, element2)
     --exception
         count = count + 1
         if count == max_attempts then
-        print("max attempts reached for space="..space.." key="..key.." field="..field)
+        print(concat{"max attempts reached for space=",space," key=",key," field=",field})
         break
         end
         box.fiber.sleep(timeout)
@@ -60,9 +62,9 @@ function increment_or_insert_2(space, key, field, element1, element2)
     end
 end
 
-field_subject = 2
-field_first = 3
-field_last = 4
+local field_subject = 2
+local field_first = 3
+local field_last = 4
 
 function update_or_insert(space, key, subject, timestamp)
     retry = true
@@ -76,7 +78,7 @@ function update_or_insert(space, key, subject, timestamp)
         --insert new tuple
         tuple = {}
         for i = 2, field_last do tuple[i] = 0 end
-        tuple[1] = string.sub(key, -8)
+        tuple[1] = sub(key, -8)
         tuple[field_subject] = subject
         tuple[field_first] = timestamp
         tuple[field_last] = timestamp
@@ -86,8 +88,8 @@ function update_or_insert(space, key, subject, timestamp)
     --exception
         count = count + 1
         if count == max_attempts then
-        print("max attempts reached for space="..space.." key="..key)
-        break
+	        print(concat{"max attempts reached for space=",space," key=",key})
+       		break
         end
         box.fiber.sleep(timeout)
     end