[GitHub] [incubator-pegasus] empiredan commented on a diff in pull request #1117: feat: introduce data sink to collect snapshot from each metric periodically

[GitBox <gi...@apache.org>]

empiredan commented on code in PR #1117:
URL: https://github.com/apache/incubator-pegasus/pull/1117#discussion_r956689572


##########
src/rdsn/include/dsn/utility/metrics.h:
##########
@@ -134,10 +135,13 @@ class metric_prototype;
 class metric;
 using metric_ptr = ref_ptr<metric>;
 
+class metric_data_sink;
+using metric_data_sink_ptr = ref_ptr<metric_data_sink>;
+
 class metric_entity : public ref_counter
 {
 public:
-    using attr_map = std::unordered_map<std::string, std::string>;
+    using attr_map = std::map<std::string, std::string>;

Review Comment:
   All of the attributes of an entity will be used as the labels of the metric. The labels will later be passed to `metric_snapshot`, thus each metric snapshot may has multiple labels. To maintain each snapshot in a map, data sink may choose to encode the labels a snapshot has, as what `metric_snapshot::encode_attributes` has done. In comparison with `std::unordered_map`, it is easier for `std::map` to be encoded since it's ordered.



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