mailserver: add DB query metrics

Useful for debugging spikes in I/O caused by SQL queries.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

mailserver/mailserver_db_leveldb.go

@@ -128,6 +128,8 @@ func (db *LevelDB) BuildIterator(query CursorQuery) (Iterator, error) {
 	defer recoverLevelDBPanics("BuildIterator")
 
 	i := db.ldb.NewIterator(&util.Range{Start: query.start, Limit: query.end}, nil)
+
+	envelopeQueriesCounter.WithLabelValues("unknown", "unknown").Inc()
 	// seek to the end as we want to return envelopes in a descending order
 	if len(query.cursor) == CursorLength {
 		i.Seek(query.cursor)

mailserver/mailserver_db_postgres.go

@@ -130,20 +130,26 @@ func (i *PostgresDB) BuildIterator(query CursorQuery) (Iterator, error) {
 
 	stmtString := "SELECT id, data FROM envelopes"
 
+	var historyRange string
 	if len(query.cursor) > 0 {
 		args = append(args, query.start, query.cursor)
 		// If we have a cursor, we don't want to include that envelope in the result set
 		stmtString += " " + "WHERE id >= $1 AND id < $2"
+		historyRange = "partial" //nolint: goconst
 	} else {
 		args = append(args, query.start, query.end)
 		stmtString += " " + "WHERE id >= $1 AND id <= $2"
+		historyRange = "full" //nolint: goconst
 	}
 
+	var filterRange string
 	if len(query.topics) > 0 {
 		args = append(args, pq.Array(query.topics))
 		stmtString += " " + "AND topic = any($3)"
+		filterRange = "partial" //nolint: goconst
 	} else {
 		stmtString += " " + fmt.Sprintf("AND bloom & b'%s'::bit(512) = bloom", toBitString(query.bloom))
+		filterRange = "full" //nolint: goconst
 	}
 
 	// Positional argument depends on the fact whether the query uses topics or bloom filter.
@@ -156,10 +162,13 @@ func (i *PostgresDB) BuildIterator(query CursorQuery) (Iterator, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	envelopeQueriesCounter.WithLabelValues(filterRange, historyRange).Inc()
 	rows, err := stmt.Query(args...)
 	if err != nil {
 		return nil, err
 	}
+
 	return &postgresIterator{rows}, nil
 }
 

mailserver/metrics.go

@@ -60,6 +60,10 @@ var (
 		Help:    "Size of envelopes saved.",
 		Buckets: prom.ExponentialBuckets(1024, 2, 11),
 	}, []string{"db"})
+	envelopeQueriesCounter = prom.NewCounterVec(prom.CounterOpts{
+		Name: "mailserver_envelope_queries_total",
+		Help: "Number of queries for envelopes in the DB.",
+	}, []string{"filter", "history"})
 )
 
 func init() {
@@ -76,4 +80,5 @@ func init() {
 	prom.MustRegister(archivedErrorsCounter)
 	prom.MustRegister(archivedEnvelopesGauge)
 	prom.MustRegister(archivedEnvelopeSizeMeter)
+	prom.MustRegister(envelopeQueriesCounter)
 }