Convert raft_entry_commit_latency to seconds & be explicit about unit

This is a follow-up to https://github.com/rabbitmq/ra/pull/160

Had to introduce mf_convert/3 so that METRICS_REQUIRING_CONVERSIONS
proplist does not clash with METRICS_RAW proplists that have the same
number of elements. This is begging to be refactored, but I know that
@dcorbacho is working on https://github.com/rabbitmq/rabbitmq-prometheus/issues/26

Also modified the RabbitMQ-Quorum-Queues-Raft dashboard

Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>

deps/rabbitmq_prometheus/docker/grafana/dashboards/RabbitMQ-Quorum-Queues-Raft.json

@@ -43,7 +43,7 @@
   "gnetId": null,
   "graphTooltip": 1,
   "id": null,
-  "iteration": 1575376605605,
+  "iteration": 1578410270904,
   "links": [
     {
       "icon": "doc",
@@ -227,7 +227,7 @@
       "reverseYBuckets": false,
       "targets": [
         {
-          "expr": "rabbitmq_raft_entry_commit_latency * on(instance) group_left(rabbitmq_cluster, rabbitmq_node) rabbitmq_identity_info{rabbitmq_cluster=\"$rabbitmq_cluster\"}",
+          "expr": "rabbitmq_raft_entry_commit_latency_seconds * on(instance) group_left(rabbitmq_cluster, rabbitmq_node) rabbitmq_identity_info{rabbitmq_cluster=\"$rabbitmq_cluster\"}",
           "format": "time_series",
           "instant": false,
           "intervalFactor": 1,
@@ -250,7 +250,7 @@
       "xBucketSize": null,
       "yAxis": {
         "decimals": null,
-        "format": "ms",
+        "format": "s",
         "logBase": 1,
         "max": null,
         "min": "0",

deps/rabbitmq_prometheus/src/collectors/prometheus_rabbitmq_core_metrics_collector.erl

@@ -129,7 +129,7 @@
         {2, disk_space_available_limit_bytes, gauge, "Free disk space low watermark in bytes", disk_free_limit},
         {2, erlang_processes_limit, gauge, "Erlang processes limit", proc_total},
         {2, erlang_scheduler_run_queue, gauge, "Erlang scheduler run queue", run_queue},
-        {2, erlang_net_ticktime_seconds, gauge, "Inter-node heartbeat interval in seconds", net_ticktime}
+        {2, erlang_net_ticktime_seconds, gauge, "Inter-node heartbeat interval", net_ticktime}
     ]},
 
     {node_persister_metrics, [
@@ -155,8 +155,7 @@
         {3, raft_log_snapshot_index, gauge, "Raft log snapshot index"},
         {4, raft_log_last_applied_index, gauge, "Raft log last applied index"},
         {5, raft_log_commit_index, gauge, "Raft log commit index"},
-        {6, raft_log_last_written_index, gauge, "Raft log last written index"},
+        {6, raft_log_last_written_index, gauge, "Raft log last written index"}
-        {7, raft_entry_commit_latency, gauge, "Time taken for an entry to be committed"}
     ]},
 
     {queue_coarse_metrics, [
@@ -201,11 +200,13 @@
         {2, 1000000, io_sync_time_seconds_total, counter, "Total I/O sync time", io_sync_time},
         {2, 1000000, io_seek_time_seconds_total, counter, "Total I/O seek time", io_seek_time},
         {2, 1000000, io_open_attempt_time_seconds_total, counter, "Total file open attempts time", io_file_handle_open_attempt_time}
+    ]},
+
+    {ra_metrics, [
+        {7, 1000, raft_entry_commit_latency_seconds, gauge, "Time taken for a log entry to be committed"}
     ]}
 ]).
 
--define(METRICS, ?METRICS_RAW ++ ?METRICS_REQUIRING_CONVERSIONS).
-
 -define(TOTALS, [
     %% ordering differs from metrics above, refer to list comprehension
     {connection_created, connections, gauge, "Connections currently open"},
@@ -227,7 +228,11 @@ collect_mf(_Registry, Callback) ->
     [begin
          Data = ets:tab2list(Table),
          mf(Callback, Contents, Data)
-     end || {Table, Contents} <- ?METRICS],
+     end || {Table, Contents} <- ?METRICS_RAW],
+    [begin
+         Data = ets:tab2list(Table),
+         mf_convert(Callback, Contents, Data)
+     end || {Table, Contents} <- ?METRICS_REQUIRING_CONVERSIONS],
     [begin
          Size = ets:info(Table, size),
          mf_totals(Callback, Name, Type, Help, Size)
@@ -295,7 +300,21 @@ mf(Callback, Contents, Data) ->
                 {Type, Fun, Data}
             )
         )
-    end || {Index, Name, Type, Help, Key} <- Contents],
+    end || {Index, Name, Type, Help, Key} <- Contents].
+
+mf_convert(Callback, Contents, Data) ->
+    [begin
+        Fun = fun(D) -> element(Index, D) / BaseUnitConversionFactor end,
+        Callback(
+            create_mf(
+                ?METRIC_NAME(Name),
+                Help,
+                catch_boolean(Type),
+                ?MODULE,
+                {Type, Fun, Data}
+            )
+        )
+    end || {Index, BaseUnitConversionFactor, Name, Type, Help} <- Contents],
     [begin
         Fun = fun(D) -> proplists:get_value(Key, element(Index, D)) / BaseUnitConversionFactor end,
         Callback(

deps/rabbitmq_prometheus/test/rabbit_prometheus_http_SUITE.erl

@@ -198,6 +198,7 @@ metrics_test(Config) ->
     %% Checking the first metric value in each ETS table that requires converting
     ?assertEqual(match, re:run(Body, "^rabbitmq_erlang_uptime_seconds ", [{capture, none}, multiline])),
     ?assertEqual(match, re:run(Body, "^rabbitmq_io_read_time_seconds_total ", [{capture, none}, multiline])),
+    ?assertEqual(match, re:run(Body, "^rabbitmq_raft_entry_commit_latency_seconds{", [{capture, none}, multiline])),
     %% Checking the first TOTALS metric value
     ?assertEqual(match, re:run(Body, "^rabbitmq_connections ", [{capture, none}, multiline])).