Log warning if histogram received cdata

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `tnt_election_leader_idle` metric.
 
+- Histogram now logs a warning if `observe` is called with `cdata` value.
+
 ## [1.0.0] - 2023-05-22
 ### Changed
 

metrics/collectors/histogram.lua

@@ -1,3 +1,5 @@
+local log = require('log')
+
 local Shared = require('metrics.collectors.shared')
 local Counter = require('metrics.collectors.counter')
 
@@ -42,11 +44,18 @@ function Histogram:set_registry(registry)
     self.bucket_collector:set_registry(registry)
 end
 
+local cdata_warning_logged = false
+
 function Histogram:observe(num, label_pairs)
     label_pairs = label_pairs or {}
     if num ~= nil and type(tonumber(num)) ~= 'number' then
         error("Histogram observation should be a number")
     end
+    if not cdata_warning_logged and type(num) == 'cdata' then
+        log.warn("Histogram observation is cdata. " ..
+            "Using cdata as observation can lead to unexpected results.")
+        cdata_warning_logged = true
+    end
 
     self.count_collector:inc(1, label_pairs)
     self.sum_collector:inc(num, label_pairs)