Receive: fix thanos_receive_write_{timeseries,samples} stats

There are two path a data can be written to a receiver: through the HTTP
or the gRPC endpoint, and `thanos_receive_write_{timeseries,samples}` only
count the number of timeseries/samples received through the HTTP
endpoint.

So, there is no risk that a sample will be count twice, once as a
remote write and once as a local write. On the other hand, we still need
to account for the replication factor, and only count local writes is
not enough as there might be no local writes at all (e.g. in RouterOnly
mode).

Signed-off-by: Mikhail Nozdrachev <mikhail.nozdrachev@aiven.io>

pkg/receive/handler.go

@@ -681,7 +681,7 @@ type remoteWriteParams struct {
 	alreadyReplicated bool
 }
 
-func (h *Handler) gatherWriteStats(writes ...map[endpointReplica]map[string]trackedSeries) tenantRequestStats {
+func (h *Handler) gatherWriteStats(rf int, writes ...map[endpointReplica]map[string]trackedSeries) tenantRequestStats {
 	var stats tenantRequestStats = make(tenantRequestStats)
 
 	for _, write := range writes {
@@ -708,8 +708,14 @@ func (h *Handler) gatherWriteStats(writes ...map[endpointReplica]map[string]trac
 		}
 	}
 
-	return stats
+	// adjust counters by the replication factor
+	for tenant, st := range stats {
+		st.timeseries /= rf
+		st.totalSamples /= rf
+		stats[tenant] = st
+	}
 
+	return stats
 }
 
 func (h *Handler) fanoutForward(ctx context.Context, params remoteWriteParams) (tenantRequestStats, error) {
@@ -739,7 +745,7 @@ func (h *Handler) fanoutForward(ctx context.Context, params remoteWriteParams) (
 		return stats, err
 	}
 
-	stats = h.gatherWriteStats(localWrites, remoteWrites)
+	stats = h.gatherWriteStats(len(params.replicas), localWrites, remoteWrites)
 
 	// Prepare a buffered channel to receive the responses from the local and remote writes. Remote writes will all go
 	// asynchronously and with this capacity we will never block on writing to the channel.