Warmup the connection pool per database (#264)

Warmup the connection pool per database

Signed-off-by: Anders Swanson <anders.swanson@oracle.com>

Author: anders-swanson

collector/collector.go

@@ -49,9 +49,18 @@ func maskDsn(dsn string) string {
 // NewExporter creates a new Exporter instance
 func NewExporter(logger *slog.Logger, m *MetricsConfiguration) *Exporter {
 	var databases []*Database
+	wg := &sync.WaitGroup{}
 	for dbname, dbconfig := range m.Databases {
-		databases = append(databases, NewDatabase(logger, dbname, dbconfig))
+		logger.Info("Initializing database", "database", dbname)
+		database := NewDatabase(logger, dbname, dbconfig)
+		databases = append(databases, database)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			database.WarmupConnectionPool(logger)
+		}()
 	}
+	wg.Wait()
 	e := &Exporter{
 		mu: &sync.Mutex{},
 		duration: prometheus.NewGauge(prometheus.GaugeOpts{

collector/database.go

@@ -4,6 +4,7 @@
 package collector
 
 import (
+	"context"
 	"database/sql"
 	"fmt"
 	"github.com/godror/godror"
@@ -64,7 +65,6 @@ func (d *Database) constLabels() map[string]string {
 
 func NewDatabase(logger *slog.Logger, dbname string, dbconfig DatabaseConfig) *Database {
 	db, dbtype := connect(logger, dbname, dbconfig)
-
 	return &Database{
 		Name:    dbname,
 		Up:      0,
@@ -74,6 +74,42 @@ func NewDatabase(logger *slog.Logger, dbname string, dbconfig DatabaseConfig) *D
 	}
 }
 
+// WarmupConnectionPool serially acquires connections to "warm up" the connection pool.
+// This is a workaround for a perceived bug in ODPI_C where rapid acquisition of connections
+// results in a SIGABRT.
+func (d *Database) WarmupConnectionPool(logger *slog.Logger) {
+	var connections []*sql.Conn
+	poolSize := d.Config.GetMaxOpenConns()
+	if poolSize < 1 {
+		poolSize = d.Config.GetPoolMaxConnections()
+	}
+	if poolSize > 100 { // defensively cap poolsize
+		poolSize = 100
+	}
+	warmup := func(i int) {
+		time.Sleep(100 * time.Millisecond)
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+
+		conn, err := d.Session.Conn(ctx)
+		if err != nil {
+			logger.Debug("Failed to open database connection on warmup", "conn", i, "error", err, "database", d.Name)
+			return
+		}
+		connections = append(connections, conn)
+	}
+	for i := 0; i < poolSize; i++ {
+		warmup(i + 1)
+	}
+
+	logger.Debug("Warmed connection pool", "total", len(connections), "database", d.Name)
+	for i, conn := range connections {
+		if err := conn.Close(); err != nil {
+			logger.Debug("Failed to return database connection to pool on warmup", "conn", i+1, "error", err, "database", d.Name)
+		}
+	}
+}
+
 func connect(logger *slog.Logger, dbname string, dbconfig DatabaseConfig) (*sql.DB, float64) {
 	logger.Debug("Launching connection to "+maskDsn(dbconfig.URL), "database", dbname)
 

main.go

@@ -110,14 +110,7 @@ func main() {
 		logger.Error("unable to load metrics configuration", "error", err)
 		return
 	}
-
-	for dbname, db := range m.Databases {
-		if db.GetMaxOpenConns() > 0 {
-			logger.Info(dbname + " database max idle connections is greater than 0, so will use go-sql connection pool and pooling settings will be ignored")
-		} else {
-			logger.Info(dbname + " database max idle connections is 0, so will use Oracle connection pool. Tune with database pooling settings")
-		}
-	}
+	
 	exporter := collector.NewExporter(logger, m)
 	if exporter.ScrapeInterval() != 0 {
 		ctx, cancel := context.WithCancel(context.Background())