WIP

pkg/servers/server.go

@@ -0,0 +1,112 @@
+package servers
+
+import (
+	"database/sql"
+	"fmt"
+	"github.com/blang/semver"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/log"
+	"sync"
+)
+
+// Server describes a connection to a Postgresql database, and describes the
+// metric maps and overrides in-place for it.
+// Also it contains metrics map and query overrides.
+type Server struct {
+	db     *sql.DB
+	labels prometheus.Labels
+	master bool
+
+	// Last version used to calculate metric map. If mismatch on scrape,
+	// then maps are recalculated.
+	lastMapVersion semver.Version
+	// Currently active metric map
+	metricMap map[string]MetricMapNamespace
+	// Currently active query overrides
+	queryOverrides map[string]string
+	mappingMtx     sync.RWMutex
+	// Currently cached metrics
+	metricCache map[string]cachedMetrics
+	cacheMtx    sync.Mutex
+}
+
+// NewServer establishes a new connection using DSN.
+func NewServer(dsn string, opts ...ServerOpt) (*Server, error) {
+	fingerprint, err := parseFingerprint(dsn)
+	if err != nil {
+		return nil, err
+	}
+
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		return nil, err
+	}
+	db.SetMaxOpenConns(1)
+	db.SetMaxIdleConns(1)
+
+	log.Infof("Established new database connection to %q.", fingerprint)
+
+	s := &Server{
+		db:     db,
+		master: false,
+		labels: prometheus.Labels{
+			serverLabelName: fingerprint,
+		},
+		metricCache: make(map[string]cachedMetrics),
+	}
+
+	for _, opt := range opts {
+		opt(s)
+	}
+
+	return s, nil
+}
+
+// Close disconnects from Postgres.
+func (s *Server) Close() error {
+	return s.db.Close()
+}
+
+// Ping checks connection availability and possibly invalidates the connection if it fails.
+func (s *Server) Ping() error {
+	if err := s.db.Ping(); err != nil {
+		if cerr := s.Close(); cerr != nil {
+			log.Errorf("Error while closing non-pinging DB connection to %q: %v", s, cerr)
+		}
+		return err
+	}
+	return nil
+}
+
+// String returns server's fingerprint.
+func (s *Server) String() string {
+	return s.labels[serverLabelName]
+}
+
+// Scrape loads metrics.
+func (s *Server) Scrape(ch chan<- prometheus.Metric, disableSettingsMetrics bool) error {
+	s.mappingMtx.RLock()
+	defer s.mappingMtx.RUnlock()
+
+	var err error
+
+	if !disableSettingsMetrics && s.master {
+		if err = querySettings(ch, s); err != nil {
+			err = fmt.Errorf("error retrieving settings: %s", err)
+		}
+	}
+
+	errMap := queryNamespaceMappings(ch, s)
+	if len(errMap) > 0 {
+		err = fmt.Errorf("queryNamespaceMappings returned %d errors", len(errMap))
+	}
+
+	return err
+}
+
+// AddQueries adds queries to the builtinMetricMaps and queryOverrides maps.
+// Added queries do not respect version requirements, because it is assumed
+// that the user knows what they are doing with their version of postgres.
+func (s *Server) AddQueries() {
+
+}