services/horizon/ingest: added more description to the history archiv…

…e metrics labels (stellar#5185)

historyarchive/archive.go

@@ -119,7 +119,8 @@ func (arch *Archive) GetCheckpointManager() CheckpointManager {
 func (a *Archive) GetPathHAS(path string) (HistoryArchiveState, error) {
 	var has HistoryArchiveState
 	rdr, err := a.backend.GetFile(path)
-	a.stats.incrementDownloads()
+	// this is a query on the HA server state, not a data/bucket file download
+	a.stats.incrementRequests()
 	if err != nil {
 		return has, err
 	}

services/horizon/internal/ingest/main.go

@@ -409,7 +409,13 @@ func (s *system) initMetrics() {
 	s.metrics.HistoryArchiveStatsCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
 			Namespace: "horizon", Subsystem: "ingest", Name: "history_archive_stats_total",
-			Help: "counters of different history archive stats",
+			Help: "Counters of different history archive requests.  " +
+				"'source' label will provide name/address of the physical history archive server from the pool for which a request may be sent.  " +
+				"'type' label will further categorize the potential request into specific requests, " +
+				"'file_downloads' - the count of files downloaded from an archive server, " +
+				"'file_uploads' - the count of files uploaded to an archive server, " +
+				"'requests' - the count of all http requests(includes both queries and file downloads) sent to an archive server, " +
+				"'cache_hits' - the count of requests for an archive file that were found on local cache instead, no download request sent to archive server.",
 		},
 		[]string{"source", "type"},
 	)