top: do polling pg_stat_statements only if it's available (issue #59)

doc/Changelog

@@ -1,4 +1,5 @@
 pgcenter (0.6.1) unstable; urgency=low
+  * top: do polling pg_stat_statements only if it's available (issue #59)
   * top: fixed handling of libpq errors during connection establishment (issue #58)
   * top: fix srong assebling of path to logfile (issue #55)
 

lib/stat/pgstat.go

@@ -79,15 +79,16 @@ type Pgstat struct {
 
 // PgInfo is the container for details about Postgres
 type PgInfo struct {
-	PgAlive         string /* is Postgres alive or not? */
-	PgVersionNum    uint   /* Postgres version in format XXYYZZ */
-	PgVersion       string /* Postgres version in format X.Y.Z */
-	PgUptime        string /* Postgres uptime */
-	PgRecovery      string /* is Postgres master or standby? */
-	PgTrackCommitTs string /* track_commit_timestamp value */
-	PgAVMaxWorkers  uint   /* autovacuum_max_workers value */
-	PgMaxConns      uint   /* max_connections value */
-	PgMaxPrepXacts  uint   /* max_prepared_transactions value */
+	PgAlive               string /* is Postgres alive or not? */
+	PgVersionNum          uint   /* Postgres version in format XXYYZZ */
+	PgVersion             string /* Postgres version in format X.Y.Z */
+	PgUptime              string /* Postgres uptime */
+	PgRecovery            string /* is Postgres master or standby? */
+	PgTrackCommitTs       string /* track_commit_timestamp value */
+	PgAVMaxWorkers        uint   /* autovacuum_max_workers value */
+	PgMaxConns            uint   /* max_connections value */
+	PgMaxPrepXacts        uint   /* max_prepared_transactions value */
+	PgStatStatementsAvail bool   /* is pg_stat_statements available? */
 }
 
 // PgActivityStat is the container for Postgres' activity stats
@@ -146,12 +147,20 @@ func (s *Pgstat) ReadPgInfo(conn *sql.DB, isLocal bool) {
 	conn.QueryRow(PgGetSingleSettingQuery, "max_connections").Scan(&s.PgMaxConns)
 	conn.QueryRow(PgGetRecoveryStatusQuery).Scan(&s.PgRecovery)
 
+	// Is pg_stat_statement available?
+	s.UpdatePgStatStatementsStatus(conn)
+
 	// In case of remote Postgres we should to know remote CLK_TCK
 	if !isLocal {
 		conn.QueryRow(PgProcSysTicksQuery).Scan(&SysTicks)
 	}
 }
 
+// UpdatePgStatStatementsStatus method refreshes info about pg_stat_availability
+func (s *Pgstat) UpdatePgStatStatementsStatus(conn *sql.DB) {
+	conn.QueryRow(PgCheckPGSSExists).Scan(&s.PgStatStatementsAvail)
+}
+
 // Reset method discards activity stats if Postgres restart detected
 func (s *Pgstat) Reset() {
 	s.PgActivityStat.ConnTotal = 0
@@ -213,9 +222,12 @@ func (s *Pgstat) GetPgstatActivity(conn *sql.DB, refresh uint, isLocal bool) {
 	conn.QueryRow(queryAutovac).Scan(
 		&s.AVWorkers, &s.AVAntiwrap, &s.AVManual, &s.AVMaxTime)
 
-	conn.QueryRow(PgStatementsQuery).Scan(&s.StmtAvgTime, &s.CallsCurr)
-	s.StmtPerSec = (s.CallsCurr - s.CallsPrev) / refresh
-	s.CallsPrev = s.CallsCurr
+	// read pg_stat_statements only if it's available
+	if s.PgStatStatementsAvail == true {
+		conn.QueryRow(PgStatementsQuery).Scan(&s.StmtAvgTime, &s.CallsCurr)
+		s.StmtPerSec = (s.CallsCurr - s.CallsPrev) / refresh
+		s.CallsPrev = s.CallsCurr
+	}
 
 	conn.QueryRow(PgActivityTimeQuery).Scan(
 		&s.XactMaxTime, &s.PrepMaxTime)

lib/stat/queries.go

@@ -16,6 +16,8 @@ const (
 	PgGetRecoveryStatusQuery = "SELECT pg_is_in_recovery()"
 	// PgGetUptimeQuery queries Postgres uptime
 	PgGetUptimeQuery = "SELECT date_trunc('seconds', now() - pg_postmaster_start_time())"
+	// PgCheckPGSSExists checks that pg_stat_statements view exists
+	PgCheckPGSSExists = "SELECT EXISTS (SELECT 1 FROM information_schema.views WHERE table_name = 'pg_stat_statements')"
 	// PgGetConfigAllQuery queries current Postgres configuration
 	PgGetConfigAllQuery = "SELECT name, setting, unit, category FROM pg_settings ORDER BY 4"
 	// PgGetCurrentLogfileQuery queries current Postgres logfile

top/context.go

@@ -153,6 +153,12 @@ func setFilter(g *gocui.Gui, v *gocui.View, answer string) {
 // Switch from context unit to another one
 func switchContextTo(c string) func(g *gocui.Gui, v *gocui.View) error {
 	return func(g *gocui.Gui, v *gocui.View) error {
+		// in case of switching to pg_stat_statements and it isn't available - keep current stats context
+		if stats.PgStatStatementsAvail == false && c == stat.StatementsView {
+			printCmdline(g, msgPgStatStatementsUnavailable)
+			return nil
+		}
+
 		// Save current context unit with its settings into context list
 		ctx.contextList[ctx.current.Name] = ctx.current
 

top/menu.go

@@ -67,6 +67,12 @@ var (
 // Open 'gocui' view object and display menu items depending on passed menu type.
 func menuOpen(m menuStyle) func(g *gocui.Gui, _ *gocui.View) error {
 	return func(g *gocui.Gui, _ *gocui.View) error {
+		// in case of opening menu for switching to pg_stat_statements and if pgss isn't available - it's unnecessary to open menu, just notify user and do nothing
+		if stats.PgStatStatementsAvail == false && m.menuType == menuPgss {
+			printCmdline(g, msgPgStatStatementsUnavailable)
+			return nil
+		}
+
 		g.Cursor = true
 
 		v, err := g.SetView("menu", 0, 5, 72, 6+len(m.menuItems))

top/stat.go

@@ -60,6 +60,11 @@ func doWork(g *gocui.Gui) {
 		break
 	}
 	printAllStat(g, stats)
+
+	// Check availability of pg_stat_statements if it's not available
+	if !stats.PgStatStatementsAvail {
+		stats.UpdatePgStatStatementsStatus(conn)
+	}
 }
 
 // Print all stats.

top/ui.go

@@ -8,6 +8,10 @@ import (
 	"time"
 )
 
+const (
+	msgPgStatStatementsUnavailable = "NOTICE: pg_stat_statements is not available in this database"
+)
+
 var (
 	errSaved error       // keep error during program lifecycle
 	cmdTimer *time.Timer // show cmdline's messages until timer is not expired