Fix summary counter

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `tnt_synchro_queue_len` metric type
 - Reset callbacks on hotreload
+- Fix queries in quantile
 
 ## [0.15.0] - 2022-08-09
 ### Fixed

metrics/quantile.lua

@@ -165,7 +165,7 @@ function stream:query(q)
 
     local p = s.l[0]
     local r = 0
-    for i = 1, s.l_len do
+    for i = 1, s.l_len-1 do  -- samples buffer indexing starts from 0 to length-1
         local c = s.l[i]
         if r + c.Width + c.Delta > t then
             return p.Value

test/integration/highload_test.lua

@@ -0,0 +1,49 @@
+require('strict').on()
+
+local fio = require('fio')
+
+local t = require('luatest')
+local g = t.group('highload')
+
+g.test_eventloop = function()
+    local tmpdir = fio.tempdir()
+    if type(box.cfg) == 'function' then
+        box.cfg {
+            wal_dir = tmpdir,
+            memtx_dir = tmpdir,
+        }
+    end
+
+    local metrics = require('metrics')
+    local fiber = require('fiber')
+    local clock = require('clock')
+    local utils = require('test.utils')
+
+    local function monitor(collector)
+        local time_before
+        while true do
+            time_before = clock.monotonic()
+            fiber.yield()
+            collector:observe(clock.monotonic() - time_before)
+        end
+    end
+
+    metrics.set_global_labels({ alias = 'my_instance' })
+
+    local collector = metrics.summary('tnt_fiber_event_loop', 'event loop time',
+        { [0.5] = 0.01, [0.9] = 0.01, [0.99] = 0.01, })
+    local fiber_object = fiber.create(function() monitor(collector) end)
+
+    for _ = 1, 10 do
+        fiber.sleep(0.1)
+        local observations = metrics.collect()
+
+        local obs_summary = utils.find_obs('tnt_fiber_event_loop',
+            { alias = 'my_instance', quantile = 0.99 }, observations)
+
+        t.assert_not_inf(obs_summary.value)
+    end
+
+    fiber.kill(fiber_object:id())
+
+end