feat(dbmanager): report pool max size and total connections opened

Add MaxOpenConnections to provider and connection stats, exposed as the
max state of dbmanager_connection_pool_size. Count physical dials through a
counting driver connector and export dbmanager_connections_opened_total;
existing_db pools derive an approximate count from sql.DBStats.

pkg/dbmanager/providers/counting.go

@@ -0,0 +1,51 @@
+package providers
+
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"sync/atomic"
+)
+
+// countingConnector wraps a driver.Connector and counts every physical
+// connection it successfully dials. sql.DBStats has no such field, so this is
+// the only way to report the total number of connections ever opened.
+type countingConnector struct {
+	driver.Connector
+	opened *atomic.Int64
+}
+
+func (c *countingConnector) Connect(ctx context.Context) (driver.Conn, error) {
+	conn, err := c.Connector.Connect(ctx)
+	if err == nil {
+		c.opened.Add(1)
+	}
+	return conn, err
+}
+
+// dsnConnector adapts a plain driver.Driver to driver.Connector.
+type dsnConnector struct {
+	dsn string
+	drv driver.Driver
+}
+
+func (c dsnConnector) Connect(context.Context) (driver.Conn, error) { return c.drv.Open(c.dsn) }
+func (c dsnConnector) Driver() driver.Driver                        { return c.drv }
+
+// openCounted is sql.Open with every dialled connection counted in opened.
+func openCounted(driverName, dsn string, opened *atomic.Int64) (*sql.DB, error) {
+	probe, err := sql.Open(driverName, dsn)
+	if err != nil {
+		return nil, err
+	}
+	drv := probe.Driver()
+	probe.Close() //nolint:gosec // G104: probe handle never dialled
+
+	var connector driver.Connector = dsnConnector{dsn: dsn, drv: drv}
+	if dc, ok := drv.(driver.DriverContext); ok {
+		if connector, err = dc.OpenConnector(dsn); err != nil {
+			return nil, err
+		}
+	}
+	return sql.OpenDB(&countingConnector{Connector: connector, opened: opened}), nil
+}

pkg/dbmanager/providers/existing_db.go

@@ -112,6 +112,12 @@ func (p *ExistingDBProvider) Stats() *ConnectionStats {
 	if p.db != nil {
 		dbStats := p.db.Stats()
 		stats.OpenConnections = dbStats.OpenConnections
+		stats.MaxOpenConnections = dbStats.MaxOpenConnections
+		// The pool was opened outside dbmanager so dials cannot be counted.
+		// Open plus every connection database/sql retired for idle or
+		// lifetime limits is a close lower bound (it misses connections
+		// dropped as broken).
+		stats.TotalOpened = int64(dbStats.OpenConnections) + dbStats.MaxIdleClosed + dbStats.MaxIdleTimeClosed + dbStats.MaxLifetimeClosed
 		stats.InUse = dbStats.InUse
 		stats.Idle = dbStats.Idle
 		stats.WaitCount = dbStats.WaitCount

pkg/dbmanager/providers/existing_db_test.go

@@ -3,9 +3,11 @@ package providers
 import (
 	"context"
 	"database/sql"
+	"sync/atomic"
 	"testing"
 	"time"
 
+	_ "github.com/glebarez/sqlite"
 	_ "github.com/mattn/go-sqlite3"
 )
 
@@ -159,6 +161,10 @@ func TestExistingDBProvider_Stats(t *testing.T) {
 		t.Errorf("Expected stats.Type to be 'sql', got '%s'", stats.Type)
 	}
 
+	if stats.MaxOpenConnections != 10 {
+		t.Errorf("Expected stats.MaxOpenConnections to be 10, got %d", stats.MaxOpenConnections)
+	}
+
 	if !stats.Connected {
 		t.Error("Expected stats.Connected to be true")
 	}
@@ -192,3 +198,35 @@ func TestExistingDBProvider_Close_NilDB(t *testing.T) {
 		t.Errorf("Expected Close to succeed with nil database, got error: %v", err)
 	}
 }
+
+func TestOpenCountedCountsDials(t *testing.T) {
+	var opened atomic.Int64
+	db, err := openCounted("sqlite", ":memory:", &opened)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+	db.SetMaxOpenConns(1)
+
+	if err := db.PingContext(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if got := opened.Load(); got != 1 {
+		t.Fatalf("opened = %d after first ping, want 1", got)
+	}
+	// Reusing the pooled connection must not count as a new dial.
+	if err := db.PingContext(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if got := opened.Load(); got != 1 {
+		t.Fatalf("opened = %d after reuse, want 1", got)
+	}
+	// Dropping idle connections forces a fresh dial.
+	db.SetMaxIdleConns(0)
+	if err := db.PingContext(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if got := opened.Load(); got != 2 {
+		t.Fatalf("opened = %d after redial, want 2", got)
+	}
+}

pkg/dbmanager/providers/mssql.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"sync/atomic"
 	"time"
 
 	_ "github.com/microsoft/go-mssqldb" // MSSQL driver
@@ -16,6 +17,7 @@ import (
 type MSSQLProvider struct {
 	db     *sql.DB
 	config ConnectionConfig
+	opened atomic.Int64
 }
 
 // NewMSSQLProvider creates a new MSSQL provider
@@ -52,7 +54,7 @@ func (p *MSSQLProvider) Connect(ctx context.Context, cfg ConnectionConfig) error
 		}
 
 		// Open database connection
-		db, err = sql.Open("sqlserver", dsn)
+		db, err = openCounted("sqlserver", dsn, &p.opened)
 		if err != nil {
 			lastErr = err
 			if cfg.GetEnableLogging() {
@@ -169,15 +171,17 @@ func (p *MSSQLProvider) Stats() *ConnectionStats {
 	stats := p.db.Stats()
 
 	return &ConnectionStats{
-		Name:              p.config.GetName(),
-		Type:              "mssql",
-		Connected:         true,
-		OpenConnections:   stats.OpenConnections,
-		InUse:             stats.InUse,
-		Idle:              stats.Idle,
-		WaitCount:         stats.WaitCount,
-		WaitDuration:      stats.WaitDuration,
-		MaxIdleClosed:     stats.MaxIdleClosed,
-		MaxLifetimeClosed: stats.MaxLifetimeClosed,
+		Name:               p.config.GetName(),
+		Type:               "mssql",
+		Connected:          true,
+		OpenConnections:    stats.OpenConnections,
+		MaxOpenConnections: stats.MaxOpenConnections,
+		TotalOpened:        p.opened.Load(),
+		InUse:              stats.InUse,
+		Idle:               stats.Idle,
+		WaitCount:          stats.WaitCount,
+		WaitDuration:       stats.WaitDuration,
+		MaxIdleClosed:      stats.MaxIdleClosed,
+		MaxLifetimeClosed:  stats.MaxLifetimeClosed,
 	}
 }

pkg/dbmanager/providers/postgres.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"math"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"go.mongodb.org/mongo-driver/mongo"
@@ -21,6 +22,7 @@ type PostgresProvider struct {
 	config    ConnectionConfig
 	listener  *PostgresListener
 	mu        sync.Mutex
+	opened    atomic.Int64
 }
 
 // NewPostgresProvider creates a new PostgreSQL provider
@@ -38,7 +40,7 @@ func (p *PostgresProvider) Connect(ctx context.Context, cfg ConnectionConfig) er
 	// The connector and *sql.DB are created once; the pool is never closed to
 	// recover from errors (see Refresh).
 	connector := newPGConnector(connCfg)
-	db := sql.OpenDB(connector)
+	db := sql.OpenDB(&countingConnector{Connector: connector, opened: &p.opened})
 
 	// Connect with retry logic
 	var lastErr error
@@ -201,16 +203,18 @@ func (p *PostgresProvider) Stats() *ConnectionStats {
 	stats := p.db.Stats()
 
 	return &ConnectionStats{
-		Name:              p.config.GetName(),
-		Type:              "postgres",
-		Connected:         true,
-		OpenConnections:   stats.OpenConnections,
-		InUse:             stats.InUse,
-		Idle:              stats.Idle,
-		WaitCount:         stats.WaitCount,
-		WaitDuration:      stats.WaitDuration,
-		MaxIdleClosed:     stats.MaxIdleClosed,
-		MaxLifetimeClosed: stats.MaxLifetimeClosed,
+		Name:               p.config.GetName(),
+		Type:               "postgres",
+		Connected:          true,
+		OpenConnections:    stats.OpenConnections,
+		MaxOpenConnections: stats.MaxOpenConnections,
+		TotalOpened:        p.opened.Load(),
+		InUse:              stats.InUse,
+		Idle:               stats.Idle,
+		WaitCount:          stats.WaitCount,
+		WaitDuration:       stats.WaitDuration,
+		MaxIdleClosed:      stats.MaxIdleClosed,
+		MaxLifetimeClosed:  stats.MaxLifetimeClosed,
 	}
 }
 

pkg/dbmanager/providers/provider.go

@@ -27,13 +27,15 @@ type ConnectionStats struct {
 	HealthCheckStatus string
 
 	// SQL connection pool stats
-	OpenConnections   int
-	InUse             int
-	Idle              int
-	WaitCount         int64
-	WaitDuration      time.Duration
-	MaxIdleClosed     int64
-	MaxLifetimeClosed int64
+	OpenConnections    int
+	MaxOpenConnections int
+	TotalOpened        int64 // physical connections ever dialled (0 when unknown)
+	InUse              int
+	Idle               int
+	WaitCount          int64
+	WaitDuration       time.Duration
+	MaxIdleClosed      int64
+	MaxLifetimeClosed  int64
 }
 
 // ConnectionConfig is a minimal interface for configuration

pkg/dbmanager/providers/sqlite.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	_ "github.com/glebarez/sqlite" // Pure Go SQLite driver
@@ -19,6 +20,7 @@ type SQLiteProvider struct {
 	db     *sql.DB
 	dbMu   sync.RWMutex
 	config ConnectionConfig
+	opened atomic.Int64
 }
 
 // NewSQLiteProvider creates a new SQLite provider
@@ -51,7 +53,7 @@ func (p *SQLiteProvider) Connect(ctx context.Context, cfg ConnectionConfig) erro
 	}
 
 	// Open database connection
-	db, err := sql.Open("sqlite", dsn)
+	db, err := openCounted("sqlite", dsn, &p.opened)
 	if err != nil {
 		return fmt.Errorf("failed to open SQLite connection: %w", err)
 	}
@@ -178,15 +180,17 @@ func (p *SQLiteProvider) Stats() *ConnectionStats {
 	stats := p.db.Stats()
 
 	return &ConnectionStats{
-		Name:              p.config.GetName(),
-		Type:              "sqlite",
-		Connected:         true,
-		OpenConnections:   stats.OpenConnections,
-		InUse:             stats.InUse,
-		Idle:              stats.Idle,
-		WaitCount:         stats.WaitCount,
-		WaitDuration:      stats.WaitDuration,
-		MaxIdleClosed:     stats.MaxIdleClosed,
-		MaxLifetimeClosed: stats.MaxLifetimeClosed,
+		Name:               p.config.GetName(),
+		Type:               "sqlite",
+		Connected:          true,
+		OpenConnections:    stats.OpenConnections,
+		MaxOpenConnections: stats.MaxOpenConnections,
+		TotalOpened:        p.opened.Load(),
+		InUse:              stats.InUse,
+		Idle:               stats.Idle,
+		WaitCount:          stats.WaitCount,
+		WaitDuration:       stats.WaitDuration,
+		MaxIdleClosed:      stats.MaxIdleClosed,
+		MaxLifetimeClosed:  stats.MaxLifetimeClosed,
 	}
 }