phia: enable prefix compression in stress test

test/phia/stress.lua

@@ -22,9 +22,13 @@ box.once("phia_stress", function()
 
     local s4 = box.schema.space.create('s4', { engine = 'phia', if_not_exists = true })
     s4:create_index('pk', {compression = 'lz4', compression_branch = 'lz4', amqf = 1, if_not_exists = true})
+
+    local s5 = box.schema.space.create('s5', { engine = 'phia'})
+    s5:create_index('pk', {compression_key = 1, amqf = 1})
 end)
 
-local spaces = {box.space.s1, box.space.s2, box.space.s3, box.space.s4}
+local spaces = {box.space.s1, box.space.s2, box.space.s3, box.space.s4,
+    box.space.s5}
 
 local function t1(ch, time_limit)
     local t1 = fiber.time()
@@ -33,7 +37,7 @@ local function t1(ch, time_limit)
         local t = math.random(80)
         local data = string.char(math.random(string.byte('Z') - string.byte('A')) + string.byte('A') - 1)
         data = data:rep(math.random(20480))
-        local space = spaces[math.mod(t, 4) + 1]
+        local space = spaces[math.mod(t, #spaces) + 1]
         if t < 32 then
             space:replace({k, data})
         elseif t < 40 then
@@ -54,7 +58,7 @@ local function t2(ch, time_limit)
     while fiber.time() - t1 < time_limit do
         local k = math.random(10000)
         local t = math.random(16)
-        local space = spaces[math.mod(t, 4) + 1]
+        local space = spaces[math.mod(t, #spaces) + 1]
         if t < 12 then
             local l = space:get({k})
         else
@@ -72,7 +76,7 @@ local function t3(ch, time_limit)
         local k = math.random(10000)
         local t = math.random(20)
         local l = math.random(2048)
-        local space = spaces[math.mod(t, 4) + 1]
+        local space = spaces[math.mod(t, #spaces) + 1]
         if t <= 6 then
             space:select(k, { iterator = 'GE', limit = l })
         elseif t <= 12 then