Merge pull request #510 from rabbitmq/ra-counters-add-num_segments

Add num_segments to Ra counters

Author: kjnilsson

src/ra.hrl

@@ -374,6 +374,7 @@
 -define(C_RA_SVR_METRIC_TERM, ?C_RA_SRV_RESERVED + 7).
 -define(C_RA_SVR_METRIC_CHECKPOINT_INDEX, ?C_RA_SRV_RESERVED + 8).
 -define(C_RA_SVR_METRIC_EFFECTIVE_MACHINE_VERSION, ?C_RA_SRV_RESERVED + 9).
+-define(C_RA_SVR_METRIC_NUM_SEGMENTS, ?C_RA_SRV_RESERVED + 10).
 
 -define(RA_SRV_METRICS_COUNTER_FIELDS,
         [
@@ -393,7 +394,9 @@
          {checkpoint_index, ?C_RA_SVR_METRIC_CHECKPOINT_INDEX, counter,
           "The current checkpoint index."},
          {effective_machine_version, ?C_RA_SVR_METRIC_EFFECTIVE_MACHINE_VERSION,
-          gauge, "The current effective version number of the machine."}
+          gauge, "The current effective version number of the machine."},
+         {num_segments, ?C_RA_SVR_METRIC_NUM_SEGMENTS,
+          gauge, "The number of non-empty segment files."}
         ]).
 
 -define(RA_COUNTER_FIELDS,

src/ra_log.erl

@@ -259,6 +259,7 @@ init(#{uid := UId,
     LastIdx = State0#?MODULE.last_index,
     put_counter(Cfg, ?C_RA_SVR_METRIC_LAST_INDEX, LastIdx),
     put_counter(Cfg, ?C_RA_SVR_METRIC_LAST_WRITTEN_INDEX, LastIdx),
+    put_counter(Cfg, ?C_RA_SVR_METRIC_NUM_SEGMENTS, ra_log_reader:segment_ref_count(Reader)),
     case ra_snapshot:latest_checkpoint(SnapshotState) of
         undefined ->
             ok;
@@ -679,12 +680,13 @@ handle_event({written, _Term, {FromIdx, _}} = Evt,
                          State#?MODULE{last_written_index_term = {Expected, Term}})
     end;
 handle_event({segments, TidRanges, NewSegs},
-             #?MODULE{cfg = #cfg{uid = UId, names = Names},
+             #?MODULE{cfg = #cfg{uid = UId, names = Names} = Cfg,
                       reader = Reader0,
                       mem_table = Mt0,
                       readers = Readers
                      } = State0) ->
     Reader = ra_log_reader:update_segments(NewSegs, Reader0),
+    put_counter(Cfg, ?C_RA_SVR_METRIC_NUM_SEGMENTS, ra_log_reader:segment_ref_count(Reader)),
     %% the tid ranges arrive in the reverse order they were written
     %% (new -> old) so we need to foldr here to process the oldest first
     Mt = lists:foldr(
@@ -1161,7 +1163,7 @@ log_update_effects(Pids, ReplyPid, #?MODULE{first_index = Idx,
 %% the Idx argument
 delete_segments(SnapIdx, #?MODULE{cfg = #cfg{log_id = LogId,
                                              segment_writer = SegWriter,
-                                             uid = UId},
+                                             uid = UId} = Cfg,
                                   readers = Readers,
                                   reader = Reader0} = State0) ->
     case ra_log_reader:update_first_index(SnapIdx + 1, Reader0) of
@@ -1178,6 +1180,7 @@ delete_segments(SnapIdx, #?MODULE{cfg = #cfg{log_id = LogId,
             NumActive = ra_log_reader:segment_ref_count(Reader),
             ?DEBUG("~ts: ~b obsolete segments at ~b - remaining: ~b, pivot ~0p",
                    [LogId, length(Obsolete), SnapIdx, NumActive, Pivot]),
+            put_counter(Cfg, ?C_RA_SVR_METRIC_NUM_SEGMENTS, NumActive),
             State = State0#?MODULE{reader = Reader},
             {State, log_update_effects(Readers, Pid, State)}
     end.